RN H KH A H NH N

KH A KH A H L U

MN L U NAN & M N MN

U LUN N H P

ti

Quantum Dots Solar Cell

GING VIN HNG DN

Th.s NG HI NG

SINH VIN THC HIN

T HONG TRNG

tp H CH MINH, thng 12 nm 2013

RN H KH A H NH N

KH A KH A H L U

MN L U NAN & M N MN

U LUN N H P

ti:

Quantum Dots Solar Cell

GING VIN HNG DN:

Th.s NG HI NG

SINH VIN THC HIN:

T HONG TRNG

tp H CH MINH, thng 12 nm 2013

Li cm n

Li u tin, em xin by t lng bit n chn thnh v su sc nht, cm n

thy Th.s NG HI NG trc tip hng dn, gip em tm hiu ti liu v

ch dy tn tnh gip em hon thnh bi tiu lun tt nghip ny.

Em xin gi li cm n cc thy c Khoa Khoa Hc Vt Liu, c bit l

cc thy c chuyn nghnh Vt Liu Nano & Mng Mng ti Trng i Hc

Khoa Hc T Nhin, HQG tp H CH MINH ging dy tn tnh v hng dn

em trong sut bn nm qua, v gip em tch ly nhng kin thc v cng qu

bu.

Xin gi nhng li cm n su sc v chn thnh nht ti cc bn lp mng

mng K10 gip mnh trong nhng nm hc qua.

Sinh vin

Hong rng

Mc lc

Mc lc ........................................................................................................................ x

M u ........................................................................................................................ 1

1. Tng quan v chm lng t ............................................................................... 2

1.1. Chm lng t l g? ................................................................................... 2

1.2. Tnh cht chm lng t ............................................................................. 3

1.2.1. Hiu ng b mt ............................................................................... 3

1.2.2. Hiu ng giam gi lng t ............................................................ 3

1.2.2.1. H ba chiu (vt liu khi) ..................... ............................ 4

1.2.2.2. H hai chiu (ging lng t) ................. ............................ 4

1.2.2.3. H mt chiu (dy lng t) ................... ............................ 5

1.2.2.4 H khng chiu (chm lng t) ............. ............................ 6

1.2.2.5. Ch giam gi ...................................... ............................ 7

1.2.3. Tnh cht quang ca chm lng t ................................................ 8

2. ng quan Pin mt tri chm lng t ............................................................ 11

2.1. Lch s v tim nng pin mt tri Vit Nam .......................................... 11

2.2. Cc th h pin mt tri .............................................................................. 13

2.2.1. Th h th nht .............................................................................. 13

2.2.2. Th h th hai ................................................................................ 13

2.2.3. Th h th ba ................................................................................. 14

2.2.3.1. PMT dng nano tinh th .................................................... 14

2.2.3.2. PMT quang in ha ......................................................... 14

2.2.3.3. PMT polymer .................................................................... 14

2.2.3.4. PMT lai ha gia tinh th ................................................. 15

2.3. Cc thng s c trng ca pin mt tri .................................................... 15

2.3.1. Dng on mch ISC ...................................................................... 15

2.3.2. Dng ti ( Idark ) ........................................................................... 16

2.3.3. Th mch h ( VOC ) ...................................................................... 17

2.3.4. Cng sut v h s lp y ca pin mt tri .................................. 17

2.3.5. Hiu sut ca pin mt tri .............................................................. 19

2.4. Cu to v nguyn l hot ng ca pin mt tri chm lng t ............. 19

2.4.1 Cu to pin mt tri chm lng t ................................................ 19

2.4.2. Nguyn l hot ng ca pin mt tri chm lng t ................... 22

2.5. Nhng ng dng ca pin mt tri ............................................................ 22

2.6. Kt lun .................................................................................................... 27

Ti liu tham kho ..................................................................................................... 28

T HONG TRNG

1

M u

Nhu cu v nng lng ca con ngi trong th k 21 l rt ln. Trong khi

cc ngun nhin liu d tr nh than , du m, kh t thin nhin ngy cng cn kit

v c d on s khng cn trong khong 200 nm ti. iu ny khin cho nhn loi

ng trc nguy c thiu ht nng lng. Vic tm kim v khai thc cc ngun nng

lng mi nh nng lng ht nhn, nng lng gi v nng lng mt tri l hng

v cng quan trng trong k hoch pht trin nng lng ton cu trong thi i cng

nghip pht trin v bo ngy nay.

Vic nghin cu s dng nng lng mt tri v nng lng sc gi ngy cng

c quan tm, nht l trong tnh hnh thiu ht nng lng nghim trng ca nc ta

trong ma kh. Nng lng Mt tri c xem l rt u vit, l ngun nng lng

sch v min ph. Hin nay Vit Nam cng nh cc nc trn th gii u c cc

trung tm nng lng Mt tri, tuy nhin y l pin mt tri v c vi qu trnh ch

to nghim ngt v phc tp.

Trong thi gian khong mi nm tr li y cc khoa hc tm ra cng ngh

ch to pin mt tri hu c.Tuy c hiu sut thp hn pin mt tri v c nhng loi pin

mt tri ny c quy trnh ch to n gin v gi thnh thp.Mt khc loi pin ny ang

trong qu trnh nghin cu nhm tng hiu sut v tui th ca pin.

Vit Nam l nc c tim nng v nng lng Mt tri, tri do t v 8Bc

n 23 Bc, nm trong khu vc c cng bc x mt tri tng i cao, vi tr s

tng x kh ln t 100- 175 kcal/cm 2 .nm. Do vic s dng Nng lng Mt tri

ca nc ta s em li hiu qu kinh t to ln.

T HONG TRNG

2

1. Tng quan v chm lng t

1.1. Chm lng t l g?

Chm lng t (Quantum dots) l nhng tinh th nano bn dn c kch thc

nh hn bn knh Bohr, l nhng h khng chiu c th giam c in t, to ra

cc mc nng lng gin on nh trong nguyn t, nn cn c gi l nguyn t

nhn to. Nhng tinh th nano bn dn c cu to t cc cp nguyn t thuc

nhng cp phn nhm nh: II-VI, III-V, IV-VI, mi chm lng t c th cha t

100-1000 nguyn t (hnh 1.1), chng hn nh cc chm lng t CdS,CdSe,ZnS,

ZnSe

Hnh 1.1: Cu trc chm lng t: (a) Cu trc ca chm lng t CdSe; (b) Chm lng

t c cu trc li-v bc CdSe/ZnS

Chm lng t c c bit ch do tim nng ng dng ca n trong nhiu lnh

vc nh thng tin lin lc, chn on y hc, sn xut LED, pin mt tri...Trong

chn on y hc, chm lng t l cng c kim tra t bo ung th, theo di qu

trnh pht trin ca chng. Trong tng lai, chm lng t c th c kt hp vi

liu php ha tr chn on v iu tr ung th. Chm lng t cn c th s

dng lm cc d trong thit b ghi hnh nh sinh hc thay th cho cht nhum hu

c do c tnh bn hn, nh c th theo di qu trnh pht trin ca t bo trong

thi gian lu hn. i vi cng ngh sn xut LED th n LED chm lng t c

u im hn n LED truyn thng nh kh nng pht x bt k bc sng no

v vic sn xut n LED pht nh sng trng cht lng tt cng c chi ph thp

hn n LED truyn thng. Trong lnh vc pin mt tri, vic s dng chm lng

T HONG TRNG

3

t hin rt c quan tm. Trong khi pin mt tri truyn thng ch to bng vt liu

bn dn c chi ph sn xut cao, hiu sut ti a ch khong 33% th pin mt tri s

dng chm lng t theo l thuyt c th t hiu sut ln n 60% vi chi ph sn

xut thp hn nhiu so vi pin mt tri truyn thng. Vi nhng c tnh th v ca

mnh, chm lng t v ang thu ht s quan tm nghin cu ca nhiu nh

khoa hc trn th gii, ha hn nhng ng dng ca n s cn c m rng trong

nhiu lnh vc cng ngh, cuc sng.

1.2. Tnh cht chm lng t

1.2.1. Hiu ng b mt

Khi vt liu c kch thc cng nh th t s gia s nguyn t trn b mt v

tng s nguyn t ca vt liu gia tng, do nguyn t trn b mt c nhiu tnh cht

khc bit so vi tnh cht ca cc nguyn t bn trong lng vt liu, nn khi kch

thc vt liu gim i th t s din tch/th tch tng ng k dn n tnh cht

quang in s khc, hay cn gi l hiu ng b mt tng.

i vi chm lng t cn c hin tng giam gi lng t;

1.2.2. Hiu ng giam gi lng t

Trong vt liu bn dn khi, cc in t trong vng dn (v cc l trng

trong vng ho tr) chuyn ng t do trong khp tinh th. Do lng tnh snght,

chuyn ng ca cc ht ti in c th c m t bng t hp tuyn tnh ca cc

sng phng c bc sng vo c nano mt, nu kch thc ca khi bn dn gim

xung, xp x gi tr ca cc bc sng ny, th ht ti in b giam trong khi ny

s th hin tnh cht ging nh mt ht chuyn ng trong mt hp th, h ht khi

c gi l h b giam gi lng t.

Di y hiu ng giam gi lng t cc ht ti in khi kch thc ca vt

liu gim s c xem xt bt u t mt m hnh in t n gin trong h ba

chiu (vt liu khi), h hai chiu (ging lng t), h mt chiu (dy lng t) v

h khng chiu (chm lng t).

T HONG TRNG

4

1.2.2.1 H ba chiu ( vt liu khi)

Trong h ba chiu, vt rn c xem nh tinh th v hn theo c ba chiu x,

y, z, chuyn ng ca cc in t c m t bng t hp tuyn tnh ca cc sng

phng c bc sng rt nh so vi kch thc ca vt liu. Khi , nng lng ca

in t t do ph thuc vo vct sng k theo hm parabol; cc trng thi phn b

gn nh lin tc (c biu th bng cc im trn hnh 1.2a) v mt trng thi

phn b lin tc v t l vi cn bc hai ca nng lng E1/2(hnh 1.2b):

Hnh 1.3(a) Nng lng ca in t t do ph thuc vo vct sng k theo hm parabol; (b) Mt trng thi tnh theo nng lng i viin t t do

1.2.2.2 H hai chiu (ging lng t)

Trong h hai chiu, cc in t c th vn chuyn ng hon ton t do trong

mt phng x-y, nhng chuyn ng ca chng theo phng z s b gii hn. Khi

kch thc ca vt rn theo phng z gim xung vo c vi nano mt (ngha l

cng bc ln vi bc sng De Broglie ca ht ti in), th ht ti in t do

trong cu trc ny s th hin tnh cht ging nh mt ht chuyn ng trong ging

th V(z), vi V(z) = 0 bn trong ging v V(z)= ti cc mt bin. V khng mt

in t no c th ra khi vt rn theo phng z, nn c th ni in t b giam

trong ging th.

Cc in t vn c th chuyn ng t do dc theo cc phng x v y, nng

lng ca in t t do ph thuc vo kx, ky theo hm parabol, cc trng thi (c

biu th bng cc im trn hnh 1.3a) phn b gn nh lin tc. Trong khi ,

T HONG TRNG

5

chuyn ng ca cc in t theo phng z b gii hn, cc in t b giam gi

trong hp. Ch c mt s nht nh cc trng thi lng t ho theo phng z

(nz=1,2 ) l c php. Mt trng thi i vi mt trng thi cho trc khng

ph thuc vo nng lng v c dng hm bc thang (hnh1.3b).

Hnh 1.4.(a) Nng lng ca in t t do ph thuc vo vc t sng kx, ky, kz theo hm

parabol; nng lng ca in t ch c th nhn cc gi tr gin on ng vi (nz=1,2)

theo phng z. (b) Mt trng thi g2d (E) h hai chiu

1.2.2.3 H mt chiu ( dy lng t)

Khi kch thc vt rn co li theo c hai chiu y, z kch thc vi nanomet

th cc in t ch c th chuyn ng t do theo phng x , cn chuyn ng ca

chng theo cc phng y v z b gii hn bi cc mt bin ca vt. Mt h nh th

c gi l dy lng t.Trong h ny, cc ht ti in c th chuyn ng ch theo

mt chiu v chim cc trng thi lng t ho hai chiu cn li. Phn b cc

trng thi, cng nh phn b cc mc nng lng tng ng, theo phng song

song vi trc x l lin tc (Hnh 1.4a). Trong khi , chuyn ng ca cc in t

dc theo hai phng cn li (phng y v phng z) b gii hn v cc trng thi

ca chng c th tm c bng cch gii phng trnh Schrdinger s dng m

hnh ht trong hp th. Kt qu l cc trng thi v b lng t ho, nhn cc gi

tr gin on (Hnh 1.4b).

T HONG TRNG

6

Hnh 1.5. (a) Phn b cc mc nng lng theo phng song song trc kx l lin tc v

dc theo ky, kz l gin on.(b)Mt trng thi g1d(E) trc kx t l

vi E-1/ 2. Mi ng hyperbol trn hnh tng ng vi mt trng thi

(ky, kz) ring bit

1.2.2.4 H khng chiu ( chm lng t)

Khi cc ht ti in v cc trng thi kch thch b giam gi trong c ba chiu

th h c gi l mt chm lng t. Trong mt chm lng t, chuyn ng

ca cc in t b gii hn trong c ba chiu (Hnh 1.5a), v th trong khng gian k

ch tn ti cc trng thi gin on (kx, ky, kz), mi mt trng thi trong khng gian

k c th c biu din bng mt im (Hnh 1.5b). Nh vy, ch c cc mc nng

lng gin on l c php (Hnh 1.5c). Cc mc nng lng ny c th c

biu din nh cc nh (delta) trong hm phn b mt chiu i vi mt trng

thi g0d(E) nh ch ra trn (Hnh 1.5d).

T HONG TRNG

7

Hnh 1.5. (a) Vt rn b co li trong c ba chiu.

(b) V hiu ng giam gi, tt c cc trng thi u l gin on v c biu din bng

mt im trong khng gian k ba chiu.

(c) Ch c cc mc nng lng gin on l c php.

(d) Mt trng thi g0d(E) dc theo mt chiu

1.2.2.5 Ch giam gi

Khi kch thc ca cht bn dn gim dn ti mc c gn bn knh Borh

exiton ca mt cp in t - l trng (a B ) ca cht bn dn th in t trong cht

bn dn th hin ra ngoi l b giam gi lng t.

Trong cc nghin cu ca tc gi Kayanuma, phn chia thnh cc ch

giam gi lng t theo kch thc sau:

Ch giam gi yu

Trong trng hp a >> aB, nng lng lin kt ca mt exciton, Eex, l ln

hn nng lng lng t ca c in t v l trng, v ph quang hc ca cc chm

lng t c xc nh bi giam gi lng t ca khi tm exciton. Nng lng

trng thi exciton c bn c cho bi:

T HONG TRNG

8

2

22g xE E

Ma

(1.1)

y Eg l nng lng vng cm ca bn dn v M = me*+ mh

*l khi lng dch

chuyn ca exciton (the exciton translation mass). Trng hp ny gi l giam gi

lng t yu v c th quan st c trong cc tinh th c kch thc ln.

Ch giam gi trung gian

Trng hp 2aB< a < 4aB, l trng chuyn ng trong th nng trung bnh v

c nh x tm ca chm lng t. Phm vi chuyn ng ca l trng xung

quanh tm tinh th nh hn rt nhiu so vi bn knh ca chm lng t v s ph

thuc kch thc ca trng thi exciton c bn c th c m t nh hnh vi ca

mt donor nh x ti tm ca chm lng t.

Ch giam gi mnh

Trng hp ny tng ng vi cc chm lng t nh , khi a

T HONG TRNG

9

1.6) c v tr cc i ti nng lng:

2 2

22

nlnl gE E

a

(1.2)

Nh vy so vi bn dn khi, b rng vng cm m rng thm mt lng:

2 2

22E

a

(1.3)

E c gi l nng lng giam gi lng t. V l do ny, quang ph ca cc

chm lng t trong ch giam gi mnh th hin s gin on v b chi phi

mnh bi kch thc ht.

Hnh 1.6 m t s cc mc nng lng chm lng t

Nh vy, mt h qu quan trng ca s giam gi lng t l m rng ca

nng lng vng cm (dch ph v pha sng ngn hay thng gi tt l dch v

pha sng xanh) khi kch thc chm lng t gim, cc mc nng lng lng t

ha tng, do nng lng tng cng ca vng cm tng v gy ra s dch xanh

ca ph hp th v ph hunh quang. S ph thuc vo kch thc ca rng

vng cm tr thnh cng c hu hiu ch to cc vt liu vi tnh cht quang

mong mun v kh nng iu khin cc tnh cht quang ca cc chm lng t

(thng qua kch thc) lm cho chng c mt v tr quan trng trong khoa hc vt

liu v cc lnh vc nh vt l, ha hc, sinh hc v ng dng k thut.

S giam hm lng t c tc dng rt ln hnh thnh nn tnh cht c trng

T HONG TRNG

10

ca h chm lng t. Do hiu ng suy gim lng t m c hai phm vi hp th v

pht x ca chm lng t u dch v pha c nng lng cao hn khi kch thc

ht gim(hnh 1.7).

Hnh 1.7a: Ph hp th ca chm lng t vi s thay i kch thc ht

Hnh 1.7b: S thay i mu sc chm lng t CdSe theo kch thc ht( dung dch

chuyn mu t xanh sang theo s tng dn kch thc ht)

T HONG TRNG

11

2. Tng quan Pin mt tri chm lng t

2.1. Lch s v tim nng pin mt tri Vit Nam

Nng lng

mt tri c s

dng t khi bt u

c s sng. T trc

cng nguyn, con

ngi bit s dng

nhit nng t mt tri

to ra la. Nhng

vi iu kin k

thut cng ngh

trc th k 19, nng

lng mt tri hu nh dng li vic si m v lm kh vt dng.

n nm 1883, pin mt tri u tin c ch to bi Charles Fritts, mt nh

pht minh ngi M. Pin mt tri ny c to ra bng cch t 1 lp selenium trn

tm kim loi sau ph l vng ln. Tuy dng in sinh ra qu nh c th s

dng, lnh vc pin mt tri ny thu ht s ch ca mt s nh khoa hc v vn

tip tc c nghin cu.

Nm 1954, cc nh khoa hc phng th nghim Bell ca M pht minh

ra pin mt tri silicon c hiu sut 4%, sau tng ln 11%. Pin silicon do phng

th nghim Bell to ra l pin mt tri u tin c in nng sinh ra vn hnh

cc thit b in thng thng.

K t , pin mt tri c u t nghin cu rt nhiu, c bit l sau

khi gi du tng nhanh t cui th k 20.

Ngy nay, nng lng mt tri l ngun nng lng c quan tm hng u

thay th ngun nhin liu ha thch ang dn cn kit. Nng lng mt tri l

ngun nng lng to ln, hu nh v tn v em li nhiu li ch lu di: l

T HONG TRNG

12

ngun nng lng sch, khng gy nhim mi trng, gim tc ng n vic

thay i kh hu

Vit Nam, cng chiu sng trung bnh l 5 kWh/m2/ngy phn ln

cc tnh min trung, min nam, v khong 4 kWh/m2/ngy cc tnh pha bc nn

c tim nng rt ln pht trin pin mt tri.

T 1975, pin mt tri c nghin cu Vin vt l. Nm 1976, pin mt

tri u tin c to ra trn lp n tinh th sillicon ti phng nghin cu quang

in ca Trung tm Nghin cu v S dng Nng lng mt tri ti TP.HCM

(CERES) thuc Vin Khoa hc Vit Nam . Trong hn 20 nm qua, nhiu loi pin

mt tri khc c pht trin Vin khoa hc v cng ngh Vit nam, v d nh:

Pin mt tri n tinh th silic, pin mt tri polysilicon, pin mt tri silic v nh

hnh, Ngoi ra cn c cc d n nghin cu v pin mt tri cht mu nhy quang

nh ti trng im HQG TP HCM Pin quang in ha trn c s tinh th nano

dioxit titan tm cht nhy quang do PGS. TS Nguyn Th Phng Thoa ch nhim

c HQG TP HCM u t kinh ph, ti Nghin cu ch to pin mt tri trn

c s vt liu TiO2 v cht mu c kim do TS. Nguyn Thanh Lc v TS. Nguyn

Th Vinh ch nhim do S KHCN TPHCM qun ly c xem nh l nhng

hng pht trin mi cho pin mt tri Vit Nam.

Trong i sng, h thng s dng nng lng mt tri cho gia nh bt u

xut hin nm 1990 v pht trin dn dn. 1999, nh my in mt tri u tin

c xy dng Gia Lai do s hp tc ca T chc pht trin cng ngh- nng

lng mi ca Nht Bn v B khoa hc cng ngh v mi trng Vit Nam. Nm

2009, Red Sun- cng ty u tin sn xut pin mt tri Vit nam- c xy dng

Long An vi cng sut hng nm 3-5 MWp. Ngoi ra c nhng cng ty rt quan

tm n vic pht trin in mt tri v ln cc d n nh : h thng mi nh

in mt tri, h thng in mt tri resort ven bin ( tp on Tun n), d n thp

sng cng cng vi nng lng mt tri ( tp on Kim nh)Tuy s cng ty u

t hot ng trong lnh vc nng lng mt tri vn cn qu t so vi tim nng ca

T HONG TRNG

13

nc ta, nhng d n trn l tn hiu tch cc cho nn cng nghip nng lng Vit

Nam.

2.2. Cc th h pin mt tri

Chm lng t c rt nhiu ng dng nh: lm cht nh du trong sensor

sinh hc, nhn din t bo ung th, lm n Led, pin mt triTrong ti ny, em

tm hiu nhng tnh cht ca chm lng t ng dng trong pin mt tri. Do ,

phn ny em xin trnh by mt s tng quan v pin mt tri v cc thng s c

trng cho pin.

2.2.1. Th h th nht

Pin mt tri c dng khi, n tinh th silic (pin mt tri kiu truyn thng)

vi hiu sut l thuyt ti a l 31%. Hin nay phn ln cc pin mt tri xut hin

trn th trng vn l th h pin mt tri th nht dng silic n tinh th vi hiu

sut 18%. Tuy nhin, nhm nghin cu ca gio s Martin Green (University of

New South Wales, c) hin nay t k lc 24.7% (trong phng th nghim).

u im ca pin ny l phm vi ph hp th rng, linh ng ht ti cao.

Tuy nhin, i hi k thut lp t , nguyn cht ca silic phi gn nh tuyt i,

gi thnh t.

2.2.2. Th h th hai

Pin mt tri c ch to theo cng ngh mng mng, cc loi vt liu to

thnh phong ph hn nh silic a tinh th, v nh hnh, CdTe, cc loi hp kim ca

CIGS (gm ng, indium, gallium v selen) v cc loi bn dn mng mng khc.

u im ca th h pin mt tri th hai l chi ph ch to t tn km, lp t n

gin hn. Hiu sut t khong 12-15%.

Dng silic v nh hnh gi r, c th to thnh nhng mng mng va t tn

km nhin liu va c kh nng hp th nng lng mt tri 40 ln cao hn silic

n tinh th. Tuy nhin , v bn cht v nh hnh (in t di ng kh khn hn

T HONG TRNG

14

nhiu so vi in t trong tinh th) nn hiu sut chuyn hon thnh in ch bng

phn na hiu sut ca silic n tinh th. Cc cht bn dn nh indium galium

dislenide ng v cadimium telluride c gi r hn rt nhiu so vi silic n phn

t, tuy nhin do c khuyt tt cu trc nn hiu sut khng cao.

2.2.3. Th h th ba

Th h pin mt tri ny rt khc so vi cc th h trc, khng da vo lp

chuyn tip p-n truyn thng . Th h pin mt tri ny bao gm: pin mt tri dng

nano tinh th, pin mt tri quang -in ha, pin mt tri cht mu nhy quang, pin

mt tri hu c.

2.2.3.1 PMT dng nano tinh th

Cc t bo nng lng mt tri da trn nn silic vi mt lp ph cc nano

tinh th (cc ht nh tinh th nano hay cc chm lng t) nh ht bn dn PbSe,

CdTe, PbS.

2.2.3.2 PMT quang in ha (PEC)

Gm mt anode quang bn dn v mt cathode kim loi c nhng trong

dung dch in phn (K3Fe(CN)

6/K

4Fe(CN)

6; I/I

3; Fe(CN)

6

4-/Fe(CN)

6

3-

;mui

sulphide/sulphur). Qu trnh phn ly in tch c thc hin bi cht bn dn v

cht in phn. Th h pin mt tri ny c u im ln l gi thnh r hn hn hai

th h trc, vic lp t v vn chuyn d dng, kch thc v hnh dng ca h rt

phong ph, c th ty chnh theo nhu cu s dng. Tuy nhin, hiu sut thng

khng cao v qu trnh ch to c th gy nhim mi trng.

2.2.3.3 PMT polymer

Nguyn tc chnh l s di chuyn in t t mt polymer/ phn t cho in t

(electron donor) n mt polymer/phn t nhn electron (electron acceptor), s di

chuyn in t s to thnh dng in. Hiu sut hin nay khong 5-6%. Mt trong

nhng pin mt tri hu c l pin mt tri polymer-fullerene (C60: polymer l cc

T HONG TRNG

15

polymer lin hp (-C=C-C=C-) nh polyacetylene (PA), polypyrrole (PPy),

polyaniline (PAn), khi ni vi cc cht thm vo (dopant) s tr thnh polymer

dn in. Khi b quang t ca nh sng mt tri kch thch, polymer lin hp

phng thch cc in t v li nhiu l trng trn mch polymer, v vy

polymer c gi l vt liu loi p. Ngc li, fullerene l vt liu nhn in t rt

hiu qu. Sau khi nhn in t fullerene mang in tch m nn c gi l vt liu

loi n.

2.2.3.4 PMT lai ha gia tinh th nano/hu c

Pin mt tri lai ha gia tinh th nano/hu c l s kt hp ca tinh th nano

v hp cht polymer .Pin mt tri ny ci thin c hiu sut hn v thn thin vi

mi trng hn.

Nguyn tc hot ng: polymer (P3HT-poly(3-hexylthiophene)) hp th

photon ca nh sng chiu ti kch thch electron t vng c bn chuyn ln vng

kch thch. Do mc nng lng vng kch thch ca polymer cao hn y vng

dn ca TiO2nn cc electron s chuyn t phn t polymer sang lp TiO2v

khuch tn ra lp in cc, cn polymer (PEDOT:PS) dn l trng ra in cc i.

Dng in c sinh ra i qua ti v tr li kt hp vi l trng, kt thc mt tin

trnh tun hon.

2.3. Cc thng s c trng ca pin mt tri

Pin mt tri l mt hay mt s thit b c thit k chuyn i quang

nng thnh in nng mt cch trc tip. Nn tng ca pin mt tri l cc t bo mt

tri (SC) hot ng da vo hiu ng quang in trong.

2.3.1. ng on mch ISC

Dng on mch l dng ca ht ti thiu s bn trong pin mt tri, hay l

dng quang in. Dng on mch ph thuc vo nh sng kch thch v bn thn

vt liu lm pin mt tri. Ta c cng thc xc nh mt dng on mch:

SC s EI q b E Q E dE (2.1)

T HONG TRNG

16

Trong , ISC l mt dng on mch, q l in tch nguyn t, bs(E) l

mt quang thng ca nh sng kch thch, QE(E) l hiu sut lng t ca pin

mt tri l xc sut m mt photon chiu ti c kh nng sinh ra mt electron

cho mch ngoi, dE l nng lng ca photon kch thch tnh trn mt n v din

tch trong mt n v thi gian.

Pin mt tri c hiu sut cao tng ng vi ISC c gi tr ln, ISC t gi tr

cc i khi th ra ca pin mt tri bng 0 tng ng trng hp pin cha ni vi

mch ngoi. Trong cc gi tr cng thc (2.1), ta thy yu t quyt nh lm thay

i hiu sut ca pin chnh l hiu sut lng t QE(E) v mt quang thng bS.

Do cn phi la chn vt liu thch hp lm pin, la chn v tr thch hp lp

rp pin mt tri trong thc t v hnh dng ca pin mt tri phi c tnh ton sao

cho QE(E) v bS t gi tr ti u.

2.3.2. Dng ti ( Idark )

Ni pin vi mch ngoi c ti, khi khng chiu sng vn c mt s chnh

lch rt nh v in tch hai u pin do c mt s lng nh ht ti c sinh ra

do chuyn ng nhit, iu ny to ra mch ngoi mt dng in gi l dng ti

Idark. Mt dng ti c tnh theo cng thc:

ar 0 1BqV

K T

d kI V I e

(2.2)

Trong : I0 l hng s, V l th ra ca pin, kBl hng s Boltzmann, T l

nhit tuyt i.

Ta thy dng ti ngc chiu vi dng on mch, do ta a vo gi tr

mt tng cng I v c xc nh nh sau:

ar 0 1B

qV

K T

SC d k SCI I I I I e

(2.3)

T HONG TRNG

17

2.3.3. Th mch h ( VOC )

Khi ni pin vi mch ngoi (c ti) v chiu sng, s chnh lch nng ht

ti rt ln hai u ca pin (electron pha n v l trng pha p) s khin th ra V

tng ln dn, khi th V t cc i, ngi ta gi n l th mch h, k hiu l VOCv

c xc nh theo cng thc:

0

ln 1SCOCIKT

Vq I

(2.4)

Khi V=VOC th (2.4) vo (2.2) ta c:

01

ar 0 1

SCI

I

d k SCI I e I

(2.5)

T (2.5) ta rt ra kt lun: Khi V = VOC th ISC= Idark, suy ra mt dng tng

cng I = ISC Idark= 0. Lc ny mch ngoi khng cn dng ht ti no, iu ny

ging nh vic ta p pin vo mt mch in b h v o th ra ca pin.

2.3.4. Cng sut v h s lp y ca pin mt tri

Cng sut ca pin mt tri c xc nh theo cng thc:

.P V I (2.6)

Trong : I nhn gi tr t 0 n ISC, V nhn cc gi tr t 0 n VOC.

Khi I = 0, ta c V = VOC v khi V = 0, ta c I = ISC. Ti hai gi tr ny ta c P =0.

Biu din P trn c tuyn I-V ca pin th hin qua hnh.

T HONG TRNG

18

Hnh 2.1 ng c tuyn I-V v th biu din cng sut ca pin

H s lp y FF l thng s ca cng sut cc i PMAX ca pin mt tri

vi tch VOC v ISC:

MP MP

SC OC

I VFF

I V (2.7)

Hnh 2.2 H s lp y th hin qua th biu din ng I-V

Trong th biu din ng I-V ( hnh 2.2), c th hiu h s lp y l t

s gia din tch hnh ch nht to bi im c cng sut cc i trn thc t Pmax

v hnh ch nht to bi im c cng sut cc i trn l thuyt PT.

H s lp y miu t cht lng ca pin mt tri. Gi tr l tng ca h s

lp y l bng 1. Trong trng hp ny mi in t sinh ra do hp th photon u

tr thnh in t dn v khng c mt mt dng in do in tr. Thc t h s lp

T HONG TRNG

19

y thng c gi tr trong khong 0,5-0,8.

2.3.5. Hiu sut ca pin mt tri

Hiu sut ca SC, k hiu l , c tnh theo cng thc:

SC OCMP MP

In In

I VI VFF

P P (2.8)

Trong : PIn l cng sut nh sng chiu ti, c trng cho s tn x ht ti trong

sut qu trnh hot ng ca pin.

Trong cc thng s lm vic ca pin mt tri, bn thng s quan trng quyt

nh tnh cht ca pin l; dng on mch ISC, th mch h VOC, h s lp y FF,

v hiu sut pin .

2.4. Cu to v nguyn l hot ng ca pin mt tri chm lng t

Pin mt tri chm lng t (QDSC) c cu to v nguyn tc hot ng

tng t nh pin mt tri cht mu nhy quang (DSC). im khc nhau gia 2 loi

pin ny l cht nhy quang. Trong khi DSC dng cc phn t cht mu nh phc

cht ca kim loi chuyn tip nh Ru, Os, Fe vi cc phi t d vng nh pyridine

hay polypyridine 2 cng, 3 cng, a cng hp th nh sng th pin QDSC dng

chm lng t bn dn.

2.4.1 Cu to pin mt tri chm lng t

Cu to ca mt pin mt tri chm lng t (QDSC) bao gm cc thnh

phn: Anode quang, dung dch cht in ly, cathode, c m t nh hnh 2.3.

T HONG TRNG

20

Hnh 2.3 Cu trc pin mt tri chm lng t nhy quang

Anode quang

Thnh phn c xem l quan trng nht trong mt pin mt tri chm lng

t l anode quang, v n nh hng ti cc thng s ca pin nh: th mch h VOC,

dng ngn mch ISC, h s lp y FF, hiu sut pin. Cu to ca mt anode quang

bao gm mng dn in trong sut (TCO transparent conducting oxides, thng l

thit pha tp Fluor (FTO) hoc pha tp Indium (ITO)). Trn mng dn in trong

sut ny c ph mt lp vt liu bn dn c nng lng vng cm rng nh

TiO2, ZnO, SnO2,v c thiu kt thnh mng li c kh nng vn chuyn in

t, thng l s dng Titan dioxit (TiO2) pha anatas, v TiO2 c nng lng vng

cm kh ln khong 3.2 eV c th hp th mt dy sng di t vng kh kin n t

ngoi rt thch hp ng dng lm pin. Chm lng t (QDs) c hp ph trn

mng TiO2 ng vai tr l ngun hp th photon t nh sng mt tri v sau

chuyn i thnh in t.

Cathode

in cc cathode l mt lp mng mng Pt c ph trn thy tinh dn

TCO. Pt c bt ti l cht xc tc hot tnh mnh dn in trn in cc i.

T HONG TRNG

21

Dung dch cht in ly

Gia hai in cc cathode v anode l dung dch in ly cha cp oxi ha -

kh, cp cht in ly I3-/I

- thng c s dng bi v cp cht xi ha kh ny

tng thch vi cc pin cht mu nhy quang Ruthnium. Tuy nhin, cht in ly

Iodide khng tng hp vi cc tinh th nano, theo thi gian chng s phn hy cc

tinh th nano v gy ra gim hiu sut pin. Cp xi ha kh S2-/Sn

2- l ph hp

nht cho cc pin mt da trn tinh th nano.

Ngoi ra, dung dch in ly s dng trong pin mt tri QDSC cha cp xy

ha kh ng vai tr chuyn in tch gia anode v cathode v ti to li chm

lng t. Mt dung dch in ly ph hp cho pin QDSC l h xy ha kh c th

xy ha kh ph hp vi gin nng lng ca chm lng t v mc Fermi

sao cho n c th ti to chm lng t hiu qu nhng vn m bo th mch

h ca pin mc cao. Ngoi ra dung dch in ly cn c nht thp thc hin

qu trnh khuch tn in tch nhanh, c im nng chy thp hn nhit mi

trng nhm hn ch s r r bay hi.

kt dnh hai in cc v gi dung dch in ly gia chng, ngn chn s

r r, bay hi ca dung dch cht in ly, ta cn dng mt vt liu kt dnh, bn

quang ha v ha hc ca vt liu ny trong dung dch cht in ly l rt quan

trng. Cc tm polymer nh Surlyn hay copolymer ca polyethylene v polyacrlylic

acide l cc cht kt dnh tt. Ngoi ra, ta cn ph thm lp keo epoxy cc mi

ni ngoi tng kn ca pin.

T HONG TRNG

22

2.4.2. Nguyn l hot ng ca pin mt tri chm lng t

Hnh 2.4: S nguyn tc hot ng ca pin mt tri chm lng t

Qu trnh 1: khi c chiu sng, chm lng t lin kt ln mng TiO2 s

hp thu nh sng ti, cc electron trong chm lng t b kch thch, s chuyn t

vng ha tr ln vng dn, li l trng vng ha tr, to thnh exciton.

*S h S (2.9)

Qu trnh 2: Do mc nng lng thp nht ca vng dn ca phn t chm

lng t cao hn mc nng lng y vng dn ca TiO2 nn cc electron s

chuyn t chm lng t sang lp TiO2 (gi l tim ht ti) v nhanh chng khuch

tn ra lp in cc, do dng in c sinh ra.

*S S e (n lp TiO2) (2.10)

Qu trnh 3,4: cc phn t chm lng t sau khi tim ht ti vo lp

TiO2 s d tha l trng vng ha tr, cc l trng ny nhanh chng ti hp vi

cc electron chyn t lp cht in ly sau qu trnh oxy ha v lm ti sinh cc

phn t chm lng t, cc qu trnh ny din ra lin tc v gip cho lp chm

lng t lun n nh.

33 2I I e

(n lp QDs) (2.11)

Qu trnh 5: Dng electron ca QDSC sau khi qua ti s c thu v cc

gp ri chuyn vo lp in ly (cp oxy ha-kh I-/I3-) thc hin qu trnh oxy ha

T HONG TRNG

23

kh b p lng electron m lp ny chuyn vo lp chm lng t, kt

thc mt qu trnh tun hon.

3 2 3I e I (e n t cc gp) (2.12)

Cc in t trn vng dn TiO2 ngoi vic chuyn ra mch ngoi cn c th

tham gia 3 qu trnh ti kt hp (phn ng dng ti).

Phn ng xy ra do s ti hp in t trong vng dn v l trng trong vng

ha tr ca TiO2.

*2( )e TiO S S (2.13)

Phn ng ca in t trn vng dn TiO2 vi cht oxy ha I3- ca cht in

ly.

2 32 ( ) 3e TiO I I

(2.14)

Phn ng xy ra nhng ni b mt thy tinh khng c che ph bi lp

oxit TiO2.

2 32 ( ) 3e SnO I I

(2.15)

Trong 3 phn ng ny, phn ng (2.14) xy ra mc ng k hn nhiu

so vi hai phn ng cn li do nng I3- ln.

2.5. Nhng ng dng ca pin mt tri trong cuc trong cuc sng

Pin mt tri chm lng t cng nh nhiu loi pin mt tri khc c ng

dng v cng rng ri trong cuc sng, cng nng nghip, kinh t, qun s, v

tinh

T HONG TRNG

24

ng dng trong cuc sng:

Ngi nh mt tri: cc tm pin mt tri c nhiu mu sc v mu m khc

nhau, c th t ln tng hoc trn mi nh v ha hp vo . Cc mi nh un

ln v nghing c th s dng c tm pin mng mng.

Hnh 2.5: pin mt tri c lp t trn nhng ngi nh

Chiu sng: l ngun in cho nhng ni cha c mng li in. pin mt

tri c h tr nhng ni vng su vng xa hoc nhng ni vng ni, ni c

nhng ngi dn tc sinh sng m cha c li in. pin mt tri cng cng l

nhng thit b in c cung cp cho nhng ni hi o, Vit Nam l qun o

trng xa,ni m c lp t ti 4.093 tm pin mt tri phc v cho nhn dn

v cc chin s trn o.

Hnh 2.6: pin mt tri c lp t nng thn v hi o phc v nng dn v chin

s

Ngun in di ng: ng dng pin mt tri trong cc thit b nh gn nh b

m khi i bin hoc i ni, thit b sc pin bng nng lng mt tri, in thoi

T HONG TRNG

25

cm ng dng nng lng mt trivi v ca in thoi c lm t nhng chai

nha ti ch, nng lng hot ng t nhng tm pin mt tri c lp phn lng

do cng ty samsung sn sut. Ti sch nng lng mt tri va tin dng va c th

trang tr hoa vn bng nhng tm pin mt tri. Pin ny gip ngi dng sc c

nhng thit b s dng in p nh nh in thoi di ng, my nghe nhc. Ngoi

nhim v sc in thoi, pin s cung cp nng lng lm sng cc si quang bn

trong ti khi ti m ra, gip ngi s dng d dng tm vt.

Hnh 2.7: pin mt tri c s dng lm ngun in di ng

T HONG TRNG

26

Nh my in nng lng mt tri: tng cng sut lp t trn ton cu ln

n 12GW (03/2013). Cc nh my t vi MW n hng trm MW, cc nc i u

l: Trung Quc, M, c Ty Ban Nha, , Php

Hin nh my nng lng mt tri c tn Agua Caliente (M) ang c tin

hnh xy dng vi cng sut -397 MW s hon thnh vo nm 2014.

Hnh 2.8: nh my nng lng mt tri

ng dng trong thit b bo v an ninh, chiu sng cng cng-n giao

thng.

Hnh 2.9: pin mt tri ng dng trong thit b an ninh v chiu sng cng cng

T HONG TRNG

27

Phng tin giao thng.

Hnh 2.10: pin mt tri ng dng trong phng tin giao thng

ng dng trong qun s, h thng thng tin-quang trc.

Hnh 2.11: pin mt tri trong qun s v cc trm pht sng, trm quan trc

T HONG TRNG

28

V tinh, tu thm him: nm 1958 VANGUARD1 l v tinh u tin s dng

ngun in c cung cp t pin mt tri c tui th ln n 6 nm.

Hnh 2.12: v tinh trong v tr c lp t bi pin mt tri

Hnh 2.13: trm v tr quc t ISS

2.6. Kt lun

Vi nhng tnh cht u vit nh rng vng cm c th iu chnh khi thay

i kch thc ht lm cho tnh cht quang thay i, hiu ng giam gi lng t

lm xut hin cc mc nng lng gin on, khi hp th 1 photon s lm bt ra

nhiu electron thay v lm bt ra 1 electron, lm cho chm lng t rt thch hp

lm pin mt tri v ci thin hiu sut pin trong khi vn duy tr c chi ph

mc thp.

Kh nng hp th vng nh sng rng t kh kin n hng ngoi nn tn

dng c ti a nng lng mt tri.

T HONG TRNG

29

Pin mt tri s dng chm lng t theo l thuyt c th t hiu sut ln

n 60% vi chi ph sn xut thp hn nhiu so vi pin mt tri truyn thng cng

nh pin mt tri mng mng.

Mc d chi ph cho QDSC l kh thp, rt d dng u t nhng nhng

nghin cu hin nay vn cha t c hiu sut cao so vi l thuyt l c th t

n 60%. Hiu sut ca pin mt tri chm lng t hin nay t hiu sut trung

bnh.

Tuy hin nay pin mt tri chm lng t cn c mt s hn ch cng nh

kh khn nht nh nh l hiu sut, nhng vi s pht trin ca cng ngh nano th

loi pin ny ha hn s t c nhng thnh cng nh mong i.

T HONG TRNG

30

TI LIU THAM KHO

ing vit

[1] Hunh L Thy Trang (2011), Tng hp v nghin cu tnh cht quang

in ca Pin mt tri chm lng t-cht mu nhy quang (QDS-DSC),

lun vn thc s, i hc khoa hoc t nhin-HQG TpHCM.

[2] Nguyn Thnh Phng, quantum dots solar cell,lun vn thc s vt l, i

hc khoa hoc t nhin-HQG TpHCM.

[3] L Phc Anh, Nghin cu tnh cht quang - in ca pin mt tri cht

mu nhy sng s dng in cc lai TiO2 - chm lng t, lun vn tt

nghip, trng i hc cng ngh-HQG-HN.

ing anh

[4] Prashant V. Kamat, Quantum Dot Solar Cells. Semiconductor Nanocrystals

as Light Harvesters J. Phys. Chem. C 2008, 112, 1873718753.

[5] http://en.wikipedia.org/wiki/Quantum_dot_solar_cell

[6] http://en.wikipedia.org/wiki/Quantum_dots

[7] Mohammad A. Halim, Harnessing Suns Energy with Quantum Dots Based

NextGeneration Solar Cell Nanomaterials 2013, 3, 22-47;

doi:10.3390/nano3010022.

[8] Sven R_hle, Menny Shalom, and Arie Zaban, Quantum-Dot-Sensitized

Solar Cells ChemPhysChem 2010, 11, 2290 2304,

www.chemphyschem.org.

[9] James McDniel, quantum dots: science and applications Nanochemistry

physics 3500.

[10] AAKASH GUPTA, quantum dots in solar cellUE 5501, E.C.E.7th

SEMESTER, U.I.E.T., PANJAB UNIVERSITY.

[11] Prof. Martin A. Green,Third Generation Photovoltaics: Advanced

Solar Energy Conversion, Springer-Verlag (Berlin, Heidelberg, 2003).