1

I HC QUC GIA H NI

TRNG I HC CNG NGH

PHM TH TUYT LAN

M PHNG V TI U HA PIN MT TRI HU C

CU TRC NAN A LP

LUN VN THC S VT LIU V LINH KIN NAN

H Ni 2012

2

I HC QUC GIA H NI

TRNG I HC CNG NGH

PHM TH TUYT LAN

M PHNG V TI U HA PIN MT TRI HU C

CU TRC NAN A LP

Chuyn ngnh: Vt liu v linh kin Nan

M s: Chuyn ngnh o to th im

LUN VN THC S VT LIU V LINH KIN NAN

NGI HNG DN KHOA HC : TS. inh Vn Chu

H Ni - 2012

6

Mc Lc

M U .......................................................................................................................... 18

Chng 1. Tng Quan V Pin Mt Tri .......................................................................... 3

1.1. Gii thiu v pin mt tri ....................................................................................... 3

1.1.1. S hp th photon ............................................................................................ 5

1.1.2. S hnh thnh v khuch tn exciton ............................................................. 6

1.1.3. S phn tch ht ti ti b mt tip xc ......................................................... 6

1.1.4. Vn chuyn ht ti ............................................................................................ 6

1.1.5. S thu thp ht ti mi in cc .................................................................. 7

1.2. S khc nhau gia pin mt tri v c v hu c ................................................. 7

1.3. Cc loi khc nhau ca pin mt tri hu c ....................................................... 12

1.3.1. Pin mt tri n lp ....................................................................................... 12

1.3.2. Pin mt tri dng chuyn tip d cht .......................................................... 13

1.4. Nguyn l hot ng ca pin mt tri hu c .................................................... 15

1.5. Exciton .................................................................................................................... 17

1.5.1. Exciton trong pin mt tri v c ................................................................... 18

1.5.2. Exciton trong pin mt tri hu c ................................................................ 18

Chng 2. M Phng Qu Trnh Hot ng ................................................................. 20

2.1. Nguyn l m hnh m phng ............................................................................... 20

2.2. Phng trnh ton hc ca in trng v suy hao nng lng quang ca

nh sng ......................................................................................................................... 22

2.3. Phng trnh khuch tn exciton trong linh kin .............................................. 26

2.4. Ti u ha cu trc linh kin ............................................................................... 29

2.4.1. Ti u ha - c s l thuyt ........................................................................... 30

Chng 3. Kt Qu V Tho Lun ................................................................................. 32

3.1. Tnh cht quang ca vt liu ................................................................................ 32

3.2. Phn b nh sng trong cu trc linh kin ......................................................... 33

7

3.3. Phn b cng in trng trong linh kin .................................................. 36

3.4. Suy gim nng lng quang trong lp hot quang ............................................ 39

3.5. Mt exiton to ra trong linh kin .................................................................... 42

3.6. Ti u ha dy lp hot quang ....................................................................... 43

Kt Lun ............................................................................................................................ 46

TI LIU THAM KHO ................................................................................................ 47

8

BNG DANH MC HNH V

Hnh 1.1. Cu to ca mt t bo nng lng mt tri in hnh. Lp mng hu c

(Organic Film) c th l mt hoc nhiu lp bn dn cng c th l mt hn hp hay

mt t hp ca chng. .......................................................................................................... 3

Hnh 1.2. Cc bc chuyn i chi tit v c ch mt mt trong t bo nng lng mt

tri. ....................................................................................................................................... 4

Hnh 1.3. Nguyn l phn ly exciton v s tch ht ti trong mt pin mt tri hu c

heterojunction. ...................................................................................................................... 5

Hnh 1.4. Cu trc ha hc ca hai loi vt liu hu c thng c s dng trong

DSSCs [16]. .......................................................................................................................... 8

Hnh 1.5. Cu trc ha hc ca mt s phn t ni ting c s dng trong OSCs

[16] ....................................................................................................................................... 9

Hnh 1.6. Cu trc ha hc ca mt s polymer ni ting c s dng trong OSCs

[16] ..................................................................................................................................... 10

Hnh 1.7. S ca mt SC v c (tri) v mt SC nhiu mi ni hu c (phi) [18] ..... 11

Hnh 1.8. Lc ca pin mt tri hu c kiu Schottky vi s vng nng lng...... 13

Hnh 1.9. Dng biu ca pin mt tri hu c heterojunction vi biu vng nng

lng ca n ....................................................................................................................... 13

Hnh 1.10. Mt s minh ha rt s b ca pin mt tri d chuyn tip khi v pin mt

tri d chuyn tip a lp [18] ........................................................................................... 14

Hnh 1.11. Gin cu trc vng trong pin mt tri d chuyn tip khi [19] ................. 15

Hnh 1.12. C ch chuyn i nh sng thnh dng in trong thit b pin mt tri v

c v hu c. ...................................................................................................................... 16

Hnh 1.13. S dch chuyn in t trong polymer (hu c):a- Polyme hp th nh

bc x mt tri to cp exiton khuych tn ti b mt chung donor acceptor; b-Ti

b mt tip xc, in t chuyn ti acceptor, to cp in t - l trng; c- S phn

tch cp in t - l trng to cc ht mang in t do; d- Cc ht mang in t do

dch chuyn theo cc pha ti cc in cc. ........................................................................ 17

Hnh 2.1. Cu trc pin quang in: thy tinh/ITO/PEDOT/PEOPT/C60/Al. ..................... 20

9

Hnh 2.2. Cu trc m lp trong thit b pin mt tri. Trong mi lp j (j=1,2...m) c

chiu dy dj v nng lng quang c m t bng chit sut phc. Nng lng in

trng mi v tr trong lp j c chia thnh hai thnh phn: nng lng in

trng dng v m tng ng vi Ej+ v Ej

-. ................................................................... 22

Hnh 2.3. dy ca C60 ti u i vi dy ca PEOPT trong khong 40nm v

60nm ................................................................................................................................... 30

Hnh 3.1. Chit sut thc ca vt liu thay i theo bc sng nh sng ti ................... 32

Hnh 3.2. Chit sut o ca vt liu thay i theo bc sng nh sng ti ...................... 33

Hnh 3.3. H s hp th nh sng ca vt liu thay i theo bc sng ti ..................... 34

Hnh 3.4. Phn x v hp th nh sng trn b mt thy tinh ca linh kin ..................... 35

Hnh 3.5. Phn b cng in trng ca mt s nh sng ti trong linh kin ........... 37

Hnh 3.6. Phn b cng in trng ca nh sng bc sng 550nm trong linh

kin: a-lp PCBM dy 80nm; b-lp PCBM dy 35nm ...................................................... 38

Hnh 3.7. Nng lng mt tri ti iu kin AM1.5 .......................................................... 40

Hnh 3.8. Gin suy gim quang nng trong lp PCBM ................................................ 41

Hnh 3.9. Gin mt exciton trong lp hot quang PCBM ca linh kin .................. 42

Hnh 3.10. Gin mt exciton trong lp hot quang PCBM ca linh kin ti iu

kin chiu sng AM1.5........................................................................................................ 43

Hnh 3.11. Gin mt dng theo b dy ca lp hot quang PCBM ti iu kin

chiu sng AM1.5 ............................................................................................................... 44

Hnh 3.12. Gin mt dng theo b dy ca lp hot quang P3HTPCBMBlend

DCB ti iu kin chiu sng AM1.5 ................................................................................ 45

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DANH MC THUT NG

Ch vit tt Ting Anh Ting Vit

A Electron acceptor Cht nhn in t

CB Conduction band Vng dn

D Electron donor Cht cho in t

EA Electron affinity i lc in t

ECD Equivalent circuit diagram S mch in tng ng

FF Fillfactor H s in y

HOMO Highest occupied molecular

orbital qu o phn t lp y cao nht

IP Ionisation potential Th ion ha

IPCE Incident monochromatic Photon

to Current collection efficiency

Hiu sut chuyn ha quang in

ton phn

ITO Indium tin oxide ITO

LUMO Lowest unoccupied molecular

orbital

Qu o phn t cha lp y

thp nht

OPV Organic photovoltaic Quang in hu c

OSCs Organic solar cells Pin mt tri hu c

PV Photovoltaic Quang in

SCs Solar cells Pin mt tri

VB Valence band Vng ha tr

1

M U

S khng hong nng lng, s nng ln ton cu, s pht thi ca kh

nh knh l mt trong nhng cn nguyn ln nht e da tng lai cuc sng

trn tri t. Bn cnh , khng hong nng lng, suy thoi kinh t hin nay

v tnh khng n nh ca trin vng sn xut du v gas l ng lc chnh cho

vic tm kim v phat trin ngu n nng lng mi t tn km hn, an ton hn

v sch hn. Trong s rt nhiu la chn v gii php an ninh nng lng bn

vng, nng lng quang in (PV) c xem xt l mt trong s cc gii php

ti u m bo an ninh nng lng m rt nhiu quc gia ang hng ti, bt

u t nghin cu c bn, trin khai th nghim ng dng v tin ti thng

mi ha. Chnh v vy, so vi cc gii php nng lng sch khc, chuyn i

quang in c nhng tin b vt bc v cng ngh, k thut v thng mi

ha.

Pin mt tri hu c la mt trong s cc thit b quang in ha hn tim

nng ng dng rng ri, a dng trong tt c mi lnh vc, t an ninh quc

phng, cng nhip n dn sinh. Pin mt tri hu c c hot ng theo

nguyn ly chuyn i anh sang thanh in nng thng qua vic s dng hp cht

hu c hot quang ph hp. Mc d c pht trin t cui nhng nm 50

ca th k truc, pin mt tri hu c khng c quan tm ng mc cho n

khi hp cht polymer lip hp c ng dng lm cht hot quang trong linh

kin, lm tng ng k hiu sut ca linh kin. Mc d vy, hiu sut ca pin

mt tri hu c vn thp so vi hiu sut pin mt tri v c. Tuy nhin, do c rt

nhiu u im, chng hn nh c th to ra mng mng trn nhiu dng vt liu

khc nhau, hay nh c th d dng ch to vi gi thnh thp, nn pin mt tri

hu c vn tip tc c nghin cu v pht trin, nhm ci thin hiu sut

chuyn ha.

Cho n nay, nhiu n lc trong hot ng nghin cu c thc hin

nhm tm hiu c ch ca pin mt tri hu c, tuy nhin, kt qu thu c cn

rt hn ch c. Pin mt tri hu c l mt trong nhng ch quan trng trong

cng nghip nng lng cng nh trong an ninh nng lng, khng nhng ca

Vit Nam m cn ca rt nhiu quc gia khc. Tuy nhin, cho d tp chung

nghin cu, nhiu vn hin vn cha c lm sng t. Chnh v vy ti

chn ti lun vn l: M phng v ti u ha cu trc pin mt tri hu

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c cu trc nan a lp, nhm m t s khuch tn ca exciton c x l

trong m hnh m phng qu trnh suy hao nng lng quang bn trong pin v

ti u ha dy ca cc lp khc nhau trong cu trc pin mt tri hu c.

ngha khoa hc v thc tin ca ti: Pin mt tri hu c l mt

trong nhng ch quan trng trong cng nghip nng lng cng nh trong an

ninh nng lng, khng nhng ca Vit Nam m cn ca rt nhiu quc gia

khc. Tuy nhin, cho d tp chung nghin cu, nhiu vn hin vn cha

c lm sng t. ti tp chung x l vn ti u v m phng ha pin mt

tri hu c cu trc a lp s dng lp hot ng quang poly(2-methoxy-5(2-

ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) (finite diference method),

bi ton m t s khuch tn ca exiton c x l trong m hnh m phng qu

trnh suy hao nng lng quang bn trong pin. iu ny cho php so snh mt

exiton v thng lng qua mt bin tip xc gia cc lp quang hot. Ti u

ha dy ca cc lp khc nhau trong cu trc pin cng c xc nh thng

qu kt qu m hnh.

Ni dung ca ti, cc vn cn gii quyt:

- Gii bi ton khuch tn ca exiton trong cu trc a lp v cu trc t

hp vi iu kin bin khc nhau.

- M phng qu trnh suy gim nng lng quang trong pin v trong tng

cu trc ca pin.

- M phng s phn b ca in trng bn trong pin cng nh tng lp

vt liu trong pin.

- Gii thch v ti u ha b dy cc lp vt liu trong pin.

- nh gi cht lng m phng v ti u ha thng qua vic ch to v

th nghim, v kho st thng s c bn mt s mu pin mt tri hu c.

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Chng 1. Tng Quan V Pin Mt Tri

1.1. Gii thiu v pin mt tri

Vic chuyn i t nh sng mt tri thnh dng in i hi s hnh

thnh ca c in tch m v in tch dng cng nh mt lc iu khin c th

y cc in tch qua mch in ngoi. Khi c kt ni vi mch in bn

ngoi, bt k thit b in no, chng hn mt mn hnh my tnh hay mt ng

c ca my bm nc, c th s dng nng lng mt tri c chuyn i.

Trn thc t, mt t bo nng lng mt tri (hnh 1.1) c th c hnh dung

nh mt ci bm m nh sng mt tri iu khin electron: Chiu cao ti a m

cc electron c th c bm tng ng vi in p cao nht m t bo

nng lng mt tri c th t c. Dng in ln nht c quyt nh bi

tc bm.

Hnh 1.1. Cu to ca mt t bo nng lng mt tri in hnh.

Lp mng hu c (Organic Film) c th l mt hoc nhiu lp bn

dn cng c th l mt hn hp hay mt t hp ca chng.

Gi s bm c th y 100 electron/s t vng ha tr (VB) ln vng dn

(CB), dng lin tc cao nht c th ca cc in t chy qua mch ngoi sau

cng l 100 electron/s. Nu dng in chy qua mch ngoi b gim i bi in

tr ti v d cn 80 electron/s th 20 electron/s cn li s ri tr li vng ha tr

trc khi chng c th tch khi t bo v c gi l dng r.

hnh 1.2 m t cc bc chuyn i ca photon thnh cc ht ti tch

bit c din ra trong t bo nng lng mt tri hu c. N cng cho thy c

4

ch mt mt lin quan v s lin h vi s lng in c s dng trong s

mch in tng ng (Equivalance Circuit Diagram - ECD).

Photon ti

Bc chuyn i C ch mt mt

Cc ht ti phn tch

ti cc in cc

Hnh 1.2. Cc bc chuyn i chi v c ch mt mt trong t bo nng lng

mt tri.

Trong cht bn dn hu c, s hp th photon dn ti vic to ra cc cp

in t v l trng lin kt (exciton) c xc sut cao hn l hnh thnh cc ht ti

t do. Cc exciton mang nng lng nhng khng th hnh thnh nn in

tch tng, c th khuch tn vo khu vc phn tch ni m nhng ht mang in

c hnh thnh. Cc ht ti cn di chuyn ti cc in cc tng ng: l

trng di chuyn ti cc m v in t ti cc dng to ra in p v sn

Hp th nh sng

To thnh Exciton

Khuch tn exciton

Phn tch ht ti

Vn chuyn ht ti

Thu thp ht ti

- Phn x (IL) Truyn qua (IL)

- Truyn qua (IL)

- Ti hp ca cc exciton (I0)

- Truyn exciton vi s ti hp ca

exciton s

au (I0)

- Khng c phn tch ht ti v sau

l ti hp ca exciton (I0)

- Ti hp ca cc ht ti (Rsh)

- linh ng gii hn ca ht ti (Rs)

- Ti hp gn cc in cc (Rsh2)

- Ro th ti cc in cc (Rs, I0)

5

sng cung cp cho mch ngoi. Qu trnh chuyn ha quang nng thnh in

nng bao gm cc bc sau:

- S hp th photon.

- S hnh thnh v khuch tn Exciton.

- S phn tch ht ti ti vng tip xc b mt.

- S vn chuyn ht ti.

- S thu ht ti mi in cc.

Hnh 1.3. Nguyn l phn ly exciton v s tch ht ti trong mt pin mt tri

hu c heterojunction.

1.1.1. S hp th photon

Trong hu ht cc linh kin OPV ch mt phn nh nh sng ti c hp

th v nhng l do sau y:

(i) rng vng cm ca vt liu bn dn qu ln. rng vng cm

khong 1.1eV (1100nm) cn c p ng hp th 77% bc x

mt tri trn tri t.

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(ii) Lp hu c qu mng. Do t ht ti v linh ng ca exciton

thp, nn yu cu dy ca lp bn dn phi di 100nm. May

mn l h s hp th ca vt liu hu c thng ln hn vt liu v

c, v d nh Silic, do ch khong 100nm l cn thit hp th

khong 60 90% nu hiu ng phn x ngc c s dng.

(iii) S phn x. S mt mt do phn x hu nh kh ng k nhng t

c kho st trong nhng vt liu hu c. Kho st cc tnh cht

ca vt liu quang in c th s cung cp nhng hiu bit v tc

ng ca chng ti s suy hao do hp th. Ph lp chng phn x

nh c s dng trong cc thit b v c chng minh vai tr

ca vic s dng bin php ngn chn hiu ng phn x.

1.1.2. S hnh thnh v khuch tn exciton

iu kin l tng l tt c exciton c kch thch phi ti c a

im phn tch. V nhng v tr phn tch c th nm ti im cui ca vt liu

bn dn, chiu di khuch tn ca chng t nht nn bng chiu di c yu cu

(cho s hp th y ) nu khng th hin tng ti t hp se xy ra vi xc

sut cao hn v nh vy photon ti s b lng ph. Khong khuch tn exciton

trong vt liu polymer thng vo khong 10nm [9,10,3,7]. Tuy nhin mt s

cht mu nh perylenes c cho l c chiu di khuch tn exciton vo khong

100nm [13].

1.1.3. S phn tch ht ti ti b mt tip xc

Phn tch ht ti xy ra b mt tip xc gia cht bn dn vi kim loi,

tp cht (v d -xy) hay gia cc kim loi nu s khc bit v i lc in t

(EA), in th ion ha (IA) vt c mc gii hn. Nu s khc bit ca lp

IA v EA l khng , cc exciton c th ch nhy ln vt liu c rng vng

cm nh hn m khng phn tch thnh cc in tch. Nhng exciton ny s ti

hp li m khng c s ng gp ht ti vo dng photon.

1.1.4. Vn chuyn ht ti

Vic vn chuyn cc ht ti b nh hng bi hin tng ti t hp trn

qung ng di chuyn ca chng n cc in cc c bit l nu cng mt

vt liu va ng vai tr nh vn chuyn trung bnh cho c electron v l trng.

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Ngoi ra, vic tng tc vi cc nguyn t hay cc ht ti khc cng lm chm

tc di chuyn do lm hn ch dng ngoi.

1.1.5. S thu thp ht ti mi in cc

xm nhp vo vt liu in cc vi cng thot tng i thp (v d

Al, Ca) cc ht ti thng phi vt qua hng ro th ca mt lp oxit mng.

Ngoi ra, kim loi c th hnh thnh mt s ngn chn lin kt vi cht bn

dn v th cc ht ti khng th ngay lp tc truyn ti lp kim loi.

Lu l c exciton v cc in tch vn chuyn trong vt liu hu c

thng i hi nhy t phn t ny sang phn t khc. Do , s ken xt ca

phn t l mt gi nh gim rng ca hiu ng ro cn phn t. Cu trc

phng ca phn t s dn n nhng c tnh vn chuyn tt hn nhng cu trc

khng gian 3 chiu. Hn na, vic ken xt cng lm tng h s hp th. tng

cng hiu qu chuyn i photon thnh cc in tch, linh kin vi cu trc

khc nhau c pht trin.

1.2. S khc nhau gia pin mt tri v c v hu c

S khc nhau c bn gia pin mt tri v c v pin mt tri hu c l

ch vt liu c s dng to thnh chng. Di gc vt liu, pin mt tri

hu c c chia thnh cc loi sau y:

1- Pin mt tri hu c cht mu nhy sng (Dye-sensitized OSCs)

2- Pin mt tri phn t (Molecular SCs)

3- Pin mt tri hu c cao phn t (polymeric SCs)

4- Pin mt tri hu c t hp (Mixed SCs)

Pin mt tri hu c cht mu nhy sng (ODSSC) c lm bng mt

cht in phn lng m vn chuyn cc ht ti mang in to ra bi cc phn t

hu c bn trong cht in phn. u im chnh ca pin mt tri hu c loi

ny l gi thnh thp. Tuy nhin, thi gian sng ca linh kin rt ngn nn hiu

sut thc t ca linh kin in quang ny l kh thp (< 1%). Hnh 1.4 m t cu

trc ha hc ca hai loi vt liu hu c thng c s dng trong DSSCs.

8

Hnh 1.4. Cu trc ha hc ca hai loi vt liu hu c thng c s dng

trong DSSCs [16].

C hai pin mt tri hu c phn t v cao phn t c lm t cc phn

t v nh hnh khng c cu trc mng tinh th. Cc thut ng phn t

(molecular) v polymeric (trng hp) da vo trng lng phn t. Thng

thng, cc cao phn t vi trng lng phn t ln hn 10000 amu c gi l

polymers. Thut ng oligomers c gn lin vi cc phn t nh hn v vi

cc phn t rt nh dng thut ng molecule c s dng [17]. Vt liu phn

t v trng hp thng c s dng cng nhau tng c hp th v tnh

dn in. Phn phn t c kh nng hp th quang tt hn trong khi polymers c

tnh dn in tt hn. Do , nng lng quang c hp th bi phn phn t

v tnh dn in c cung cp bi li cc chui polymer, l nguyn nhn tng

hiu sut chuyn ha ca loi linh kin ny.

Hnh 1.5 v hnh 1.6 theo th t cho thy cc cu trc ha hc ca mt s

vt liu phn t v trng hp c s dng trong ch to pin mt tri hu c vi

tn vit tt ca chng.

9

Hnh 1.5. Cu trc ha hc ca mt s phn t ni ting c s

dng trong OSCs [16]

10

Hnh 1.6. Cu trc ha hc ca mt s polymer ni ting c s

dng trong OSCs [16]

S khc bit ln khc gia pin mt tri hu c v pin mt tri thng

thng l do c ch pht sinh ht ti v truyn ht ti. Trong pin mt tri v c

sau khi hp th mt photon, mt in t c kch thch v mt cp in t - l

trng c to ra. Nh in trng pht sinh, cc ht ti in, ty theo du v

11

th in ng, s tri dt v pha cc dng (anode) (cho in t) v cc m

(cathode) (cho l trng). Hnh 1.7 m t s mch ca mt pin mt tri da

vo c ch pht ht ti bn trong SC. Trong trng hp ca pin mt tri hu c,

in t v l trng lin kt cht ch vi nhau v to mt exciton (hnh 1.7).

Hnh 1.7. S ca mt SC v c (tri) v mt SC nhiu mi ni

hu c (phi) [18]

Nng lng lin kt ca exciton hu c v nng lng phn ly ca chng

thng khc nhau v nh hn so vi ca exciton bn dn truyn thng. phn

ly exiton thnh cc ht ti, phi c mt nng lng ln ph v nng lng

lin kt ny. Tuy nhin, trong trng hp exciton hu c, c s khc bit khi

phn tch chng thnh ht ti so vi trng hp ca cc exiton bn dn khc.

Mt exciton trong mt phn on hu c (mt phn t hoc mt chui polymer)

l bng trng thi kch thch ca phn on . N l mt trong cc trng thi n

nh trong trng thi nng lng khng lin tc ca phn on v c lin

quan n mt hnh thi qu o n nh ca cc vng in t ca phn khc .

V vy, s ph v mt exciton hu c l tng ng vi mt s thay i trong

trng thi n nh, i hi mt lng nng lng nhiu hn nng lng do lc

ht Coulomb sinh ra gia chng. Mt khc, khng ging nh cht bn dn thng

12

thng, vt liu polymer dn khng c cu trc mng tinh th. Nhng ht ti

n l trong mt vt liu hu c c gi cht ti mt v tr v c gi l

polarons. Do , trc khi tch ht ti nn c mt phn t th hai mang cha

ht ti c sinh ra. iu ny c ngha l c nng lng cn thit ph v mt

exciton cn phi nhiu hn. Sau khi exiton b phn tch thnh ht ti, bn thn

chng khng th c ht ti bt c cc in no do in trng n. Tuy nhin,

chng c th khch tn trong khng gian vt liu. Nh vy, nu ht ti cng di

chuyn n mt lp dn, in t v l trng s c kt hp b mt ca lp

dn , ti t hp thnh cc exiton v kt qu l khng c nng lng in c

to ra. Do , in t v l trng cn phi c phn dng. to mt cp in

t - l trng t mt exciton, mt trong cc iu kin sau y nn tn ti:

1- in trng cao

2- B mt chung ca hai vt liu vi hai vng nng lng khc nhau.

Nh in th sn c trong pin mt tri hu c, s dng a mi ni, iu

kin th hai c s dng trong cu trc ca OSCs ph v cc exciton. Trong

phn tip theo, cc cu trc khc nhau ca OSCs c tho lun.

1.3. Cc loi khc nhau ca pin mt tri hu c

1.3.1. Pin mt tri n lp

Tng t pin mt tri v c, loi pin hu c ph bin thng thy l

pin mt s dng vt liu quang hot loi n hoc loi p (hu ht loi p). Pin mt

tri ny cn c gi bng tn Schottky OSC do c tnh chuyn tip Schottky

ca thi b. Hnh 1.8 m t cu trc v biu vng ca mt pin mt tri kiu

Schottky.

13

Hnh 1.8. Lc ca pin mt tri hu c kiu Schottky vi s

vng nng lng

1.3.2. Pin mt tri dng chuyn tip d cht

Vi pin n lp hay pin Schottky, do khng c b mt tip xc d cht,

hu ht cc exciton c to ra s phn tch b mt tip xc hay bn trong cc

lp hot quang m khng pht ra bt c mt nng lng no. Nh vy, c th

thy rng, tng hiu sut phn tch exiton, cn tng cng vng phn tch vi

mc nng lng hp l. Do , cu trc c xut l s dng hai loi vt

liu hu c hot quang vi vng nng lng ph hp v v vy c gi l cu

trc d hp nht d chuyn tip (hay OSC tip xc kp). Hnh 1.9 cho thy dng

biu v biu vng ca mt pin mt tri d chuyn tip.

Hnh 1.9. Dng biu ca pin mt tri hu c heterojunction vi biu vng

nng lng ca n

Trong cu trc ny, nh sng n t in cc dng trong sut s b hp

th v sinh ra mt exciton. Exciton ny khuch tn tt theo tt c cc hng (7-

10 nm) ti b mt tip xc ca lp cho v nhn ni m chng c tch ra thnh

mt l trng v mt in t. Sau , ht ti ny s tip cn in cc nh cch lc

in trng cng nh hin tng khuch tn, v s to ra dng in..

Nh cp, do chiu di khuch tn ca exiton kh ngn khng phi

tt c exciton tip cn c b mt tip xc v, m c mt phn s b ti hp. V

vy, tng nng lng in s gim v hiu sut s gim. khc phc hin

tng ny, c th to ra cc lp hot quang ccos dy mng, nhng iu ny

c th dn n hin tng gim cng hp th nh sng ca linh kin.

14

gii quyt vn ca cu trc tip xc d cht dng mng, mt gii

php c a ra o l phi trn cc vt liu quang hat khc nhau thnh dng

t hp khi lp quang hot. Vi gii php ny din tch b mt tip xc c

tng ln, nn cc exciton trc khi kt hp li c c may tch ri nhau ra

ti b mt tip xc. Loi OSC ny c gi l OSC tip xc khi (BHJOSC).

Hnh 1.10 cho thy s khc bit trc quan gia hai dng cu trc ny, theo

mu en th hin lp nhn v mu trng th hin lp cho.

Hnh 1.10. Mt s minh ha rt s b ca pin mt tri d chuyn tip khi v

pin mt tri d chuyn tip a lp [18]

Nh c th c nhn thy trong hnh, trong pin mt tri d chuyn tip

khi hai vt liu ny c trn vi nhau. V vy, b mt tip xc ca lp cho v

lp nhn tng dn n s exciton c tch ra thnh in t v l trng c

tng ln. T l ny c gi l hiu sut lng t v l mt trong nhng c tnh

c s dng nh gi hiu sut ca pin mt tri.

Trong pin mt tri hu c d chuyn tip khi, sau khi phn tch exciton,

in t s i ti qu o phn t cha in y thp nht (LUMO) ca lp nhn,

iu l tng t vng dn trong cht bn dn thng thng, v cc l trng

s i ti qu o phn t in y cao nht (HOMO) ca lp cho, tng ng

nh vng ha tr ca cht bn dn thng thng. Trong trng hp ny, hn hp

pha trn ca vt liu cho v nhn ng vai tr nh vt liu hu c mi vi vng

cm ngn hn so vi LUMO ca cht nhn v HOMO ca cht cho.

15

Hnh 1.11. Gin cu trc vng trong pin mt tri d chuyn tip khi [19]

1.4. Nguyn l hot ng ca pin mt tri hu c

So snh s khc bit trong hnh thnh dng in ca pin mt tri hu c

v v c c th th hin trc quan bng hnh 1.12.

16

Hnh 1.12. C ch chuyn i nh sng thnh dng in trong thit b pin mt

tri v c v hu c.

C th thy rng, s khc nhau c bn trong vic hnh thnh dng l sau

khi hp th nng lng nh sng mt tri ti lp hot quang th i vi vt liu

v c in t nhy t vng ha tr ln vng dn v li vng dn mt l trng

in t v l trng ny s khuch tn n cc in cc hnh thnh dng mch

ngoi nh hnh trn. Trong khi , vi vt liu hu c, in t b kch thch nhy

ln trng thi kch thch hnh thnh nn exiton. V in t c in tch m (-) v

l trng mang in dng (+) to nn cp m dng (-)(+), hay l l trng - in

t (exciton), chng lin kt vi nhau do lc ht tnh in. Cp (+)(-) phi c

tch ri in t hon ton t do i li to ra dng in. Cc exciton s b phn

tch thnh in t, l trng t do ti cc a im c th no trong vt liu

hay b mt bin gia vt liu v cc tp cht (oxy, hydro, v.v) hoc b mt bin

gia vt liu v cc lp vt liu khc. Vng exciton b phn tch thnh in t,

l trng ring r gi l vng phn tch (dissociation). Sau khi phn tch, in t

s chuyn ng trong vt liu tin n cc dng v l trng chuyn ng trong

vt liu tin n cc m. Dng in xut hin.

17

Hnh 1.13. S dch chuyn in t trong polymer (hu c):a- Polyme hp th

nh bc x mt tri to cp exiton khuych tn ti b mt chung donor

acceptor; b-Ti b mt tip xc, in t chuyn ti acceptor, to cp in t - l

trng; c- S phn tch cp in t - l trng to cc ht mang in t do; d-

Cc ht mang in t do dch chuyn theo cc pha ti cc in cc.

1.5. Exciton

Nh bit, trong cc tinh th bn dn, exciton l cp in t - l trng

c lin kt vi nhau bng tng tc Coulomb. Chng c to ra khi vt liu

hot quang c chiu sng (photon), hoc c th c to ra bi s lin kt cc

in tch tri du trong cc linh kin in hunh quang di tc dng ca in

trng [19]. Nng lng cn thit to ra chng phi ln hn hoc bng

rng vng cm ca vt liu. Exciton l phn t trung ho in c th di chuyn

t do khp tinh th v truyn nng lng kch thch, nhng khng truyn in

tch. Khi nim exciton cng c m rng cho cc cht bn dn phn t. Khi

phn t polymer dn nhn c nng lng kch thch (nh sng in trng,

v.v) ln th in t nm trong vng HOMO s nhy ln vng LUMO, to ra

in t trong vng LUMO v li l trng trong vng HOMO. Do tng tc

tnh in, in t v l trng lin kt vi nhau to thnh cp gi l exciton. Cc

exciton cn c phn tch ra trc khi ht ti c th c vn chuyn qua

lp mng v c thu li tai cc in cc. V d s phn tch exciton c th xy

18

ra 1 b mt chnh lu (lin kt Schottky) trong thit b n lp hoc l x ra

b mt bin gia vt liu bn dn cho v nhn in t. B mt cng ln th

cng c nhiu exciton c th chm ti v b phn tch. Ngoi ra, khong

khuch tn nh ca exciton (thng vo khong 10nm) so vi chiu dy ca

mng cn thit hp th phn ln nh sng ti (thng > 100nm) lm cho n

kh c th t ti hiu sut chuyn i cao trong t bo nng lng mt tri.

1.5.1. Exciton trong pin mt tri v c

Nng lng lin kt ca exciton c c tnh khong 16meV ngha l

cc exciton tr nn quan trng ch yu nhit thp (khi m kT tr nn nh

so vi Eb)[8]. Khng ging nh cc thnh phn ht ca n, mt exciton v c

th ging mt Boson hn l mt Fecmion, vi thi gian sng c th hin bi

phng trnh Bose-Einstein. Cc exciton c th gim nng lng ca bn thn

thm na nu chng c gn vi nhng tp cht hoc khuyt tt. V chng l

Boson nn tt c chng c th chim gi mc nng lng thp nht (1 ln) to ra

nhng nh nhn trong nh sng pht ra nhit thp so cc bc x ti t hp

ca cc thnh phn in t v l trng. mt cao v nhit thp, kh

exciton t do c th ngng t to ra cp in t - l trng pha lng vi

nhiu tnh cht th v[18].

1.5.2. Exciton trong pin mt tri hu c

Nng lng lin kt Eb ca cc exciton trong vt liu bn dn hu c - c

bit l cho cc polymer lin hp nh PPV v cc dn xut ca n - nhn c

nhiu s tranh lun mnh m trong sut thp nin qua. Gi tr Eb dao ng trong

khong t rt nh[14] so vi gi tr trung bnh (khong 0.4eV) ti gi tr rt cao

(ln ti 0.95eV) [2]. Tuy nhin mt s b p gia cc mc HOMO v LUMO

ca vt liu D/A vn cn c p ng exciton c th phn r nhit

phng.

Cc exciton c phn loi nh sau:

- Frenkel Exciton: Cp in t l trng c gii hn trong 1 n v

nh hn 1 phn t.

- Mott-Wannier exciton: Khong cc gia in t v l trng ln hn

nhiu so vi khong cch gia cc n v t bo pin [15, 17] ( y

l cc n v phn t). Nng lng ca chng c m t nh l

19

trng thi lin kt hydro v c tnh ton vi thng qua s gim

khi lng.

- Exciton truyn in tch: Exciton m rng hn 1 vi phn t lin k

[12].

- Exciton chui lin hp: Thut ng ny c s dng cho cc cht

bn dn polymer ch ra rng nhng thnh phn ht ti nm trn

cc chui polymer khc nhau. N c th c coi l mt exciton

truyn in tch.

- Exciton ni chui: Thut ng ny cng cp ti cc cht bn dn

polymer ch ra rng cc thnh phn ht ti nm trn cng mt

chui polymer. Ngi ta tin rng cc exciton chui ni th hin cho

loi exciton chnh c hnh thnh sau khi cc polymer lin hp

chu s kch thch quang [4, 5, 6].

20

Chng 2. M Phng Qu Trnh Hot ng

2.1. Nguyn l m hnh m phng

Hnh 2.1. Cu trc pin quang in: thy tinh/ITO/PEDOT/PCBM/Ca/Al.

Qu trnh u tin dng in trong pin mt tri hu c c to ra

l s hnh thnh cp in t l trng (exiton) bi s hp th nng lng ca nh

sng. Khi c to ra, exiton c thi gian sng c xc nh thng qua s ti

hp pht x hay khng pht x, hay bi s phn tch thnh cc ht ti t do. Qu

trnh mong mun chnh l qu trnh phn tch cc exiton thnh cc ht ti t do

v c th bt gi ht ti ny ti in cc. S phn tch exiton thnh ht ti c th

din ra nh tc ng bi mt in trng no hoc bi tng tc ca chnh

exiton vi b mt bin, vi tp cht hay vi cc khim khuyt ni m s truyn

in tch c th din ra. Nguyn nhn do khong khuch tn ca exiton thng

21

b gii hn nn ch nhng exiton no c v tr phn tch nm trong gii hn

khuch tn mi hnh thnh nn dng in.

Nguyn l c bn vn dng cho m phng s suy gim nng lng quang

bn trong pin mt tri hu c nm ch coi nh sng kch hot pin c bn cht

sng in t trng. S dng phng trnh chun tc do Ghosh v Feng a ra

m t qu trnh chuyn ha in trng nh sng thnh dng in trong pin.

M phng c da theo nhng gi thit sau:

1. Cc lp mng trong kt cu pin l lin tc v ng hng, do vy c th

s dng chit sut phc m t hin tng kch thch quang.

2. Mt phng tip gip gia cc lp song song nhau v phng so vi bc

sng nh sng.

3. nh sng ti c xem xt l sng phng.

4. Dng hnh thnh trong pin do cc exiton b phn tch ti mt bin.

5. Vng khuch tn ca exiton khng ph thuc vo nng lng b kch

thch.

6. Mi ht ti c to ra s hnh thnh nn dng, ngha l khng xy ra hin

ti kt hp gia cc ht ti.

22

2.2. Phng trnh ton hc ca in trng v suy hao nng lng

quang ca nh sng

Hnh 2.2. Cu trc m lp trong thit b pin mt tri. Trong mi lp j (j=1,2...m)

c chiu dy dj v nng lng quang c m t bng chit sut phc. Nng

lng in trng mi v tr trong lp j c chia thnh hai thnh phn: nng

lng in trng dng v m tng ng vi Ej+ v Ej

-.

Trn hnh trn thy rng kt cu ca pin gm m lp bn v hn. Trong

mi lp j (j=1,2...m) c chiu dy dj v tnh cht quang ca n c m t bi

chit sut phc j=nj + ikj trong chit sut ph thuc vo bc sng ti. in

trng ti mi im c phn thnh hai thnh phn: thnh phn truyn theo

hng x v thnh phn truyn theo hng ngc li l Ej+ v Ej

-. Ma trn b mt

bin (ma trn chit sut) c th hin nh sau:

11

1

jk

jk

jkjk

rI

rt

(2.1)

Trong , rjk v tjkl h s phn x v truyn qua Fresnel ti b mt bin

jk. Vi nh sng ti c in trng vung gc vi mt phn cc (sng TE), rjk

v tjk c xc nh nh sau:

j k

jk

j k

q qr

q q

(2.2)

23

2 jjk

j k

qt

q q

(2.3)

Trong in trng song song vi mt phng ti (sng TM) th rjk v tjk

c xc nh nh sau:

2 2

2 2

k j j k

jk

k j j k

n q n qr

n q n q

(2.4)

2 2

2 2

2 k j jjk

k j j k

n n qr

n q n q

(2.5)

Trong :

qj = j cos j = [ j2 n0

2 sin 0]

1/2

v 0 chit sut ca khng kh, 0 l gc ti ca nh sng chiu vo.

Ma trn lp (ma trn pha) m t qu trnh truyn sng nh sng qua lp j

c m t nh sau:

-0

0

j j

j j

i d

jk

j i d

eL

e

(2.6)

Trong

2j jq

(2.7)

vi jdj l dy pha ca lp mng j tng ng vi s thay i v pha ca sng.

Bng cch s dng ma trn L v ma trn I trn, ma trn tn x S

(scattering matrix) biu din cho in trng ti mt tip xc vi khng kh v

mt c tnh ton theo phng trnh 2.8:

0 1

0 1

m

m

SE EE E

(2.8)

24

Ma trn S c tnh ton bng phng trnh sau:

11 12

1 1

121 22

m

vv v m m

v

S SS I L I

S S

(2.9)

Do nh sng ti t khng kh v theo chiu thun nn sng s khng

truyn bn trong theo chiu nghch, ngha l E-m+1=0.

Phn x v truyn qua cho ton h c biu din bi cc phng trnh

2.10 v 2.11.

0 21

0 11

E Sr

E S

(2.10)

1

0 11

1mEtE S

(2.11)

tnh ton in trng bn trong lp j, h c chia thnh 2 phn, phn

cch nhau bi lp j. iu ny c ngha l s tn ti hai h ma trn S tng xng

vi mi phn.

' "

j j jS S L S

(2.12)

Ma trn S ng vi tng phn s c xc nh nh sau:

Vi phn tri:

'0

0

j

j

j

EES

EE

(2.13)

' ' 111 12'

1 1' '121 22

jj j

j vv v j j

vj j

S SS I L I

S S

(2.14)

y, Ej+ v Ej

- l in trng tng ng vi bn tri ca mt bin (j-1)j ca

lp j.

25

Vi phn phi:

"

' 1

"

1

j m

j

j m

E ES

E E

(2.15)

" "

11 12"

1 1'' "121 22

mj j

j vv v m m

v jj j

S SS I L I

S S

(2.16)

Truyn qua, phn x ti pha tri v phi ca lp j c xc nh nh sau:

'

12'

'

11

j

j

j

Sr

S (2.17)

'

'

11

1j

j

tS

(2.18)

"

12"

"

11

j

j

j

Sr

S (2.19)

"

"

11

1j

j

tS

(2.20)

Kt hp 2.10 n 2.20 ta c h s truyn vn bn trong pin l:

'

2' "0 1

j j

j j

j i d

j j

E tt

E r r e

(2.21)

2' "

2"

2' "0 1

j j

j j

j j

i d

i dj j j

j j ji d

j j

E t r et t r e

E r r e

(2.22)

Vi phng trnh 2.21 v 2.22, in trng ti mt phng bt k trong lp

j cch b mt bin (j-1)j v pha phi c xc nh nh sau:

26

0

j j

j j

j

i x i x

j j

E x E x E x

t e t e E

(2.23)

V s lng trng thi kch thch ti mt im trong tng lp ph thuc

trc tip vo nng lng b hp th bi vt liu, s tiu hao nng lng ca

trng in t trong vt liu l mt i lng rt c ngha i vi pin mt tri.

Nng lng suy hao mi giy trong lp j ti v tr x c xc nh bi cng thc

sau:

2

0

1

2j j j jQ x c E x

(2.24)

Vi c tc nh sng, hng s in mi ca chn khng, v h s hp

th nh sng ca lp j nj l chit sut lp j. H s hp th nh sng c xc

nh bng cng thc sau.

4 j

j

k

(2.25)

2.3. Phng trnh khuch tn exciton trong linh kin

Trong ti liu gii quyt vn ca khuch tn exciton (gi nh rng sau

khi b kch thch s lng exciton theo s phn b nh sng) nh l:

0( )xS x I e (2.26)

Phng trnh 2.26 ng rng S(x) (s lng exciton) s b gim theo hm

m vi khong cch (x) t nhng im ti. Tuy nhin, s thc rng exciton, nh

l mt s ht khc, khuch tn n nhng ni ln cn. Do , gi nh rng tng

s ht mang in trong s Exciton (n(x)) v tr x( khong cch trong vng kch

thch), l nguyn do khuch tn v suy gim, phng trnh mt exciton tr

thnh:

27

2

1

2( )

n n nD Q x

t x h

(2.27)

Trong phng trnh ny, Q(x) l nng lng hp th c tnh ton t

phn trc, D l chiu di khuch tn, l thi gian sng ca exciton, 1 l nng

lng trao i exciton, v h nng lng nh sng ti.

Gii bng phng php vi phn hu hn c th kt lun rng phng trnh

2.27 l phng trnh khuch tn exciton (ni m exciton thc hin nh l

khuch tn ht trong) v nh l phng trnh khuch tn khc, n bao gm ba

phn:

- Gii hn khuch tn ( do hp th khng ng u t nh sng)

- Gii hn tiu tn (do exciton phn ly)

- Gii hn pht sinh (do pht sinh exciton)

Trong trng thi n nh (ni m thi gian pht sinh ca n l 0), phng

trnh 2.27 c th c vit li:

22 1

2( ) ( )

d nn x Q x

dx Dh

(2.28)

Trong phng trnh trn l nghch o ca chiu di khuch tn.

1 1L D

(2.29)

S dng gii php phn tch trong phng trnh 2.28, n(x) s l

''1

1 22 2

4( ) . . . . os

( )

x x xTNn x Ae B e C e C c d xD

(2.30)

Trong phng trnh trn N s lng photon trn mt n v b mt, h s

() l i s trong h s tn x c tnh ton trong phn TM v C1 v C2 c

xc nh di y:

2 2

1 ''dC e (2.31)

28

2 2

2 22

2 ''4

dC e

(2.32)

Do , A v B trong phng trnh 2.30 l cha bit. xc nh hai gi

tr ny, iu kin bin s c p dng. Gi nh rng exciton s b gim trong

qu trnh trong qu trnh khuch tn v hon ton phn ly b mt tip xc,

tng s lng exciton bin s bng 0 (n(x) =0 bin). Do thay th iu

kin bin trong phng trnh 2.30, v gii quyt gi tr cha bit trong hai

phng trnh, gi tr A, B c tnh ton:

1 2

4. os '' os ''d d d d d

d d

e e C e e C e c d c

Ae e

(2.33)

1 2

4. os '' os ''d d d d d

d d

e e C e e C e c d c

Be e

(2.34)

Phn b exciton cng nh chc nng tng v tr mt dng khuch tn

exciton b mt tip xc trong lp tch cc c th c vit nh pht sinh

exciton phn b:

Ex0

c

x

dnJ D

dx (2.35)

Exc

x d

dnJ D

dx (2.36)

Bng gi nh rng, tc trao i cho mt exciton mt truyn

dn (=2 v

29

oto ExPh cJ q J (2.37)

Trong cu trc kp, tnh ton c dng c ton b thit b s bng v

s c hng i din trong iu kin dng ngn mch. Do , s dng mt trong

phng trnh 3.35 v 3.36 dng quang in ngn mch trong pin mt tri hu c

c th c tnh ton:

oto 1 22 2

4. . . . .sin ''d d d dPh x d

q TNJ Ae B e e C e C

(2.38)

2.4. Ti u ha cu trc linh kin

Pin mt tri hu c c nh gi nh l mt gii php tim nng thay

th cho pin mt tri silic nh chi ph thp v n gin trong vn ch to cng

nh x l rc thi pht sinh trong qu trnh s dng [1-6]. Nh gii php vt liu

t hp chuyn tip d cht, hiu sut ca OPV c tng ln ng k [7-12].

Vi cu trc dng ny, vt liu poly (3-hexylthiophene) v phenyl C61-butyric

acid methyl ester chng t l mt trong s nhng vt liu cho thy s thnh

cng trong vic ci tin hiu sut chuyn ha. Gn y, c nhiu n lc hn

nng cao hiu sut ca pin quang in hu c bng cch nng cao s hp th

nh sng. Tuy nhin, bt chp nhng ci tin , hiu sut ca linh kin s dng

vt liu d cht chuyn tip hu c vn cha cao c th c thng mi

ha.

Nhiu nghin cu c tin hnh xc nh s nh hng hnh thi

hc ca lp vt liu hot quang n thuc tnh quang in ca linh kin OPV.

Trong s , m hnh khuch tn l mt trong nhng nghin cu c gi tr m

thng qua c th d on cc thng s c bn ca linh kin. Nghin cu ca

Barker ch dy ca lp quang hot ti u cho linh kin OPV bng cch

gi thuyt rng ch mt phn nh nng lng nh sng ti b tiu hao trong qu

trnh hnh thnh exiton. Buxton v Clark pht trin m hnh hai chiu da

trn nguyn l phn x v in ng hc m phng qu trnh to ra in tch

trong h vt liu cha pha nhn v cho. Kt qu nghin cu t m hnh ny

ch ra s nh hng ca hnh thi hc cng nh l kch c in trng.

30

2.4.1. Ti u ha - c s l thuyt

ti u ha dy ca lp quang hot trong OPV, mt s cch tip cn

c s dng. Mt trong s cch tip cn c s dng l cc i ha

cng in trng ti b mt ca lp hot quang. Cch tip cn ny da vo

nguyn l mt excitons cng ln nu gi tr |E(x)|2 cng ln. Hnh 2.3 cho

thy ln ca in trng ti b mt PEOPT/C60 v a ra mt dy lp ti

u l 31 nm cho C60 [11]. Tuy nhin, nu chng ta tip tc lm gim dy ca

PEOPT, gi tr |E(x)|2 s tip tc gia tng v dy ti u ca PEOPT s tip

cn ti 0, iu ny l khng ph hp.

Hnh 2.3. dy ca C60 ti u i vi dy ca PEOPT trong

khong 40nm v 60nm

Trong thc t, cc i ha |E (x)|2 s khng thc s ti a ha hiu sut

ca linh kin, v lc ch quan tm n vai tr ca cng in trng m

khng xem xt n hin tng khuch tn ca excitons. gii quyt nhc

im ca cch tip cn thng qua cc i ha cng in trng, mt cch

tip cn khc c la chn l ti u ha mt dng tng ng vi tng

bc sng ca nh sng ti.

31

1

1 2 1

,

jx d

n xJ q D

x

(2.39)

Trong q l in tch ht ti, 2 hiu sut chuyn ha in exciton thnh

ht ti, v dj l dy ca lp donor. Tng t nh vy, c th tnh ton mt

dng ca lp acceptor bng cng thc sau:

2

2 2 2

0

,

x

n xJ q D

x

(2.40)

Gi s rng cc ht ti in ch pht sinh b mt tip gip ca cc lp

hot ng. Nh vy, mt dng tng thu c s l:

1 2

1 2

0

, ,

j

photon

x d x

n x n xJ q D D

x x

(2.41)

vi gi nh rng 2 = 1.

Hiu sut chuyn ha quang in ton phn (IPCE), c tnh ton theo

cng thc sau:

0

1240Photo

JIPCE

I

(2.42)

Trong I0 l cng ban u. Nu xem xt s phn b quang ph ca nh

sng mt tri I(), dng tng trong linh kin c th c xc nh bng phng

trnh sau y

TotalJ IPCE I d (2.43)

32

Chng 3. Kt Qu V Tho Lun

3.1. Tnh cht quang ca vt liu

Chit sut phc ca vt liu theo bc sng nh sng c xc nh bng

phng php phn tch ph elipsometric. Hnh 3.1 v 3.2 biu din chit sut

thc v o tng ng ca vt liu ITO, PEDOT, PCBM, Ca v Al c s dng

trong m hnh cu trc linh kin OPV.

300 400 500 600 700 8001

1.5

2

2.5

3

3.5

Wavelength (nm)

Refr

acti

on

In

dex

, n

ITO

PEDOT

PCBM

Ca

Al

Hnh 3.1. Chit sut thc ca vt liu thay i theo bc sng nh sng ti

33

300 350 400 450 500 550 600 650 700 750 8000

0.5

1

1.5

2

2.5

3

3.5

Wavelength (nm)

Re

fr

ac

tio

n I

nd

ex

, k

ITO

PEDOT

PCBM

Ca

Al

Hnh 3.2. Chit sut o ca vt liu thay i theo bc sng nh sng ti

3.2. Phn b nh sng trong cu trc linh kin

S hp th nh sng ca tng lp cu trc trong linh kin thay i theo

ph nh sng mt tri c bc sng trong khong 300 n 800 nm c xc

nh bng cng thc 2.25 v biu din trong hnh 3.3.

34

300 400 500 600 700 8000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Wavelength (nm)

Lig

ht

Inte

nsi

ty F

ra

cti

on

ITO

PEDOT

PCBM

Ca

Al

Hnh 3.3. H s hp th nh sng ca vt liu thay i theo bc sng ti

Theo , c th thy rng, vi mng PCBM hp th cc i nhn c

bc sng 400 nm v gim nhanh khi bc sng trong gii t 400 n 600 nm.

Vi PEDOT, hp th hu nh khng i t di sng 400 n gn 500 nm v

tng t ngt t vng 500 n 600nm v gi mc cao t bc sng trn 600

tr i.

Vi mng ITO, phn ln vng t ngoi b hp th. y l mt tnh cht

ph hp bo v polymer khi s lo ha ca tia t ngoi. Trong vng nh

sng nhn thy, mng ITO hp th cc i bc sng 447 nm (2,76eV).

35

nh sng phn x trn b mt thy tinh ca in cc truyn qua c

tnh ton theo cng thc 2

R r trong r nhn c t phng trnh 2.10 v

2.11 c biu din trong hnh 3.4

300 350 400 450 500 550 600 650 700 750 8000

0.1

0.2

0.3

0.4

0.5

Wavelength (nm)

Lig

ht

Inte

nsi

ty F

ra

cti

on

300 350 400 450 500 550 600 650 700 750 8000.5

0.6

0.7

0.8

0.9

1

Reflectance

Absorption

Hnh 3.4. Phn x v hp th nh sng trn b mt thy tinh ca linh kin

Do lp Al ca linh kin c dy ln hn m xuyn ca nh sng

nn tng lng nh sng b hp th bi linh kin c th c biu din bng

A=1-Reflectance. Phn nh sng b hp th bi linh kin th hin trong hnh 3.4

(ng lin) phn nh gii hn cc i phn quang nng thc t c th chuyn

ha thnh dng in ca linh kin. Theo kt qu tnh ton, c th thy rng trong

ph nh sng nhn thy linh kin c th hp th thp nht 56% v hp th nhiu

36

nht khong 85%. Do , thy tinh l hp th chim u th hn so vi phn x

nn thy tinh c chn lm trong vt liu.

3.3. Phn b cng in trng trong linh kin

Cng in trng nh sng ti mi im trong linh kin c tnh

ton bng cng thc 2.23. Hnh 3.5 biu din s phn b gi tr MSE (2

E )ca

bc sng 350, 450, 550, 650 v 750 nm bn trong linh kin.

37

0 50 100 150 200 250 300 350 400 4500

0.5

1

1.5

2

2.5

ITO PEDOT PCBM Ca Al

Position in Device (nm)

No

rm

ali

zed

Ele

ctr

ic f

ield

in

ten

sity

|E

|2

350 nm

450 nm

550 nm

650 nm

750 nm

Hnh 3.5. Phn b cng in trng ca mt s nh sng ti

trong linh kin

Nh trnh by, mt exiton t l vi gi tr MSE ca nh sng ti bn

trong linh kin, ch s chit sut v cng hp th nh sng ca vt liu.

Quan st trn hnh 3.5, nhn thy rng gi tr MSE b gin on ti b mt bin

ca cc lp vt liu. iu ny c gii thch bi s thay i gi tr ca chit

sut thc n v h s dp tt k thay i ti b mt bin. Hnh 3.5 cng cho thy,

vi nh sang ti khc nhau th gi tr MSE trn mi lp cng s khc nhau.

38

thy r s nh hng ca dy lp vt liu hot quang n phn b

ca MSE trong n, tnh ton c thc hin khi ch thay i dy lp PCBM

trong khi cc lp vt liu khc vn gi nguyn. Kt qu c biu din trong

hnh 3.6.

0 50 100 150 200 250 300 350 400 4500

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

ITO PEDOT PCBM Ca Al

Position in Device (nm)

No

rm

ali

zed

Ele

ctr

ic f

ield

in

ten

sity

|E

|2

550 nm

(a)

0 50 100 150 200 250 300 350 4000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

ITO PEDOT PCBM Ca Al

Position in Device (nm)

No

rm

ali

zed

Ele

ctr

ic f

ield

in

ten

sity

|E

|2

550 nm

(b)

Hnh 3.6. Phn b cng in trng ca nh sng bc sng 550nm trong

linh kin: a-lp PCBM dy 80nm; b-lp PCBM dy 35nm

39

C th thy rng, gi tr ca MSE trong lp hot quang PCBM b nh

hng rt mnh bi dy ca mng. iu ny cho thy, c th iu chnh

dy ca lp hot quang thay i c tnh ca linh kin. Bn cnh , cng c

th nhn thy rng MSE hu nh suy gim nhanh chng ti b mt bin ca

PCBM v Ca. Chnh v vy, c th coi mt tip xc PCBM/Ca l b mt bin

bn trong linh kin.

T hnh 3.5 v 3.6, c th thy rng, b mt PEDOT/PCBM l b mt

bin hot ng chnh ca linh kin. a s cc exiton s b phn tch ti b mt

ny. Do vy vic m rng din tch b mt ny l mt trong nhng gii php

gia tng hiu sut chuyn ha ca linh kin.

3.4. Suy gim nng lng quang trong lp hot quang

Lp hot quang l thnh phn quan trng trong linh kin v phn ln

exiton c sinh ra trong lp ny. Kho st s suy gim nng lng nh sng

trong lp hot quang s c th nh tnh nh gi c c tnh ca linh kin.

Nng lng nh sng ti cho tnh ton suy gim quang nng trong linh kin

c xc nh iu kin AM1.5 v biu din trong hnh 3.7.

40

300 400 500 600 700 8000

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

Wavelength (nm)

Lig

ht

Inte

nsi

ty,W

/cm

2

Hnh 3.7. Nng lng mt tri ti iu kin AM1.5

ng c tnh suy gim quang nng trong lp vt liu ny nhn c

bng cch s dng phng trnh 2.24.

41

120 140 160 180 200 220 240 2600

2000

4000

6000

8000

10000

12000

14000

Position in Device (nm)

Dis

sip

ate

d E

nn

erg

y m

W/(

sec-c

m2)

350 nm

450 nm

550 nm

650 nm

750 nm

Hnh 3.8. Gin suy gim quang nng trong lp PCBM

C th nhn thy rng quang nng tiu hao trong lp hot quang b nh

hng chi phi bi bc sng. Hn th na, c th nhn thy, suy hao nng

lng ch yu din ra ti khu vc gia ca lp quang hot. Nh vy c th thy

rng, a phn exiton c sinh ra ti vng trung tm ca lp quang hot. y l

kt qu ng ch v nu lp hot quang qu dy, phn ln exciton s khng th

n c b mt bin PEDOT/PCBM phn tch thnh ht ti v nh vy, c

th lm gim hiu sut chuyn ha ca linh kin.

42

3.5. Mt exiton to ra trong linh kin

Mt exciton c tnh ton bng phng trnh 2.30 v c biu din

trong hnh 3.9 theo cc bc sng 350, 450 550, 650 v 750 nm.

120 140 160 180 200 220 240 2600

0.5

1

1.5

2

2.5

3x 10

19

Position in Device (nm)

Gen

era

tio

n r

ate

/(s

ec-c

m3)

350 nm

450 nm

550 nm

650 nm

750 nm

Hnh 3.9. Gin mt exciton trong lp hot quang PCBM ca linh kin

Kiu thay i ca gin mt exiton kh ging vi kiu gin ca

nng lng suy hao. iu ny c gii thch l do gi s khng c s

chuyn i quang nng thnh nhit nng v ton b nng lng quang nng

chuyn ha thnh nng lng kch thch to exciton nn hai th ny kh

ging nhau. Vi ph nh sng mt tri iu kin AM1.5, gin mt

exciton theo v tr c tnh ton bng phng trnh 3.28 v th hin trong hnh

3.10.

43

140 160 180 200 220 2401

1.5

2

2.5

3

3.5

4

4.5

5x 10

21

ITO PEDOT PCBM Ca Al

Position in Device (nm)

Gen

era

tio

n r

ate

/(s

ec-c

m3)

Hnh 3.10. Gin mt exciton trong lp hot quang PCBM ca linh kin

ti iu kin chiu sng AM1.5

3.6. Ti u ha dy lp hot quang

Da theo nguyn l dng cc i ti u ha b dy lp hot quang

trong linh kin vi cc iu kin sau:

- Cu trc linh kin:

Thy tinh/ITO_110nm/PEDOT_25/PCBM/Ca_7nm/Al_200nm;

- Ch thay i chiu dy mng PCBM;

- Hiu sut lng t ni IQE=100%;

44

Gin miu t s ph thuc ca mt dng in theo b dy lp quang

hot c th hin trong hnh 3.11.

0 20 40 60 80 1000

1

2

3

4

5

6

Layer thickness (nm)

Cu

rren

t D

en

sity

(m

A/c

m2)

Maximized

point

Hnh 3.11. Gin mt dng theo b dy ca lp hot quang PCBM ti

iu kin chiu sng AM1.5

C th thy rng, vi dy khong 72nm, linh kin s dng PCBM l

vt liu quang hot cho mt dng ln nht. Php ti u c thc hin vi

linh kin s dng vt liu P3HT:PCBM blend DCB lm vt liu hot quang.

Kt qu c ch ra trong hnh 3.12.

45

0 20 40 60 80 100 120 1400

2

4

6

8

10

12

Layer thickness (nm)

Cu

rren

t D

en

sity

(m

A/c

m2)

Maximized

Point

Hnh 3.12. Gin mt dng theo b dy ca lp hot quang P3HT:PCBM

blend DCB ti iu kin chiu sng AM1.5

Theo kt qu trong hnh 3.13, c th d on, linh kin OPV s dng vt

liu P3HT:PCBM blend DCB s cho cc i dng in ngoi nu b dy ca lp

hot quang trong khong 80nm.

46

Kt Lun

Da vo kt qu m phng, kch thc ca tng lp trong cu trc pin

c ti u ha. Thng s v tnh cht quang ca vt liu hot quang dng

acceptor: Poly(3,4-ethylenedioxythiophene) (vit tt l PEDOT) v dng donor:

[6,6]-phenyl-C61 butyric acid (vit tt l PCBM) c s dng trong m

phng v ti u ha. Phng php sai phn hu hn c s dng gii cc

phng trnh khuch tn ca exciton v trin khai n trong tnh ton suy hao

nng lng quang trong pin khi pin ch lm vic. Mt v cng dng

exiton qua b mt bin tip xc ca cc lp mng cng c tnh ton. Trn c

s kt qu tnh ton, dy ti u ca lp mng PCBM c xc nh c l

72 nm tng ng. V khi ta thay lp hot quang PCBM bng lp hn hp hot

quang P3HT:PCBM blend DCB th xc nh c dy ti u ca lp hn

hp hot quang l 80 nm.

47

TI LIU THAM KHO

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Ting Anh

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Mc LcBNG DANH MC HNH V DANH MC THUT NG M U Chng 1. Tng Quan V Pin Mt Tri 1.1. Gii thiu v pin mt tri 1.1.1. S hp th photon 1.1.2. S hnh thnh v khuch tn exciton1.1.3. S phn tch ht ti ti b mt tip xc 1.1.4. Vn chuyn ht ti 1.1.5. S thu thp ht ti mi in cc 1.2. S khc nhau gia pin mt tri v c v hu c 1.3. Cc loi khc nhau ca pin mt tri hu c 1.3.1. Pin mt tri n lp 1.3.2. Pin mt tri dng chuyn tip d cht1.4. Nguyn l hot ng ca pin mt tri hu c 1.5. Exciton 1.5.1. Exciton trong pin mt tri v c 1.5.2. Exciton trong pin mt tri hu c Chng 2. M Phng Qu Trnh Hot ng 2.1. Nguyn l m hnh m phng 2.2. Phng trnh ton hc ca in trng v suy hao nng lng quang ca nh sng 2.3. Phng trnh khuch tn exciton trong linh kin 2.4. Ti u ha cu trc linh kin 2.4.1. Ti u ha - c s l thuyt Chng 3. Kt Qu V Tho Lun 3.1. Tnh cht quang ca vt liu 3.2. Phn b nh sng trong cu trc linh kin 3.3. Phn b cng in trng trong linh kin 3.4. Suy gim nng lng quang trong lp hot quang3.5. Mt exiton to ra trong linh kin 3.6. Ti u ha dy lp hot quang Kt Lun TI LIU THAM KHO