Ag2Se量子點(diǎn)共敏化固態(tài)染料敏化太陽能電池光電性能研究

楊英, 潘德群, 張政, 陳甜, 韓曉敏, 張力松, 郭學(xué)益

?

Ag2Se量子點(diǎn)共敏化固態(tài)染料敏化太陽能電池光電性能研究

楊英1,2,3, 潘德群1,2,3, 張政1,2,3, 陳甜1,2,3, 韓曉敏1, 張力松1, 郭學(xué)益1,2,3

(1. 中南大學(xué) 冶金與環(huán)境學(xué)院, 長沙 410083; 2. 有色金屬資源循環(huán)利用湖南省重點(diǎn)實(shí)驗(yàn)室, 長沙 410083; 3. 有色金屬資源循環(huán)利用湖南省工程研究中心, 長沙 410083)

采用水相共沉積法制備Ag2Se量子點(diǎn)(QDs), 并與染料共敏化制備固態(tài)染料敏化太陽能電池(DSSCs)。考察了Ag2Se量子點(diǎn)不同敏化方式(TiO2/N719/QDs, TiO2/QDs/N719)及敏化時(shí)間(0~5 h)對(duì)DSSCs性能的影響。通過透射電子顯微鏡(TEM)和紫外-可見光譜圖(UV-Vis)對(duì)Ag2Se量子點(diǎn)結(jié)構(gòu)及光學(xué)性質(zhì)進(jìn)行了表征; 采用光調(diào)制光電流/電壓譜(IMPS/VS)以及交流阻抗譜(EIS)對(duì)器件中載流子傳輸過程進(jìn)行了研究。TiO2/QDs/N719的電池器件比TiO2/ N719/QDs具有更高的單色光量子轉(zhuǎn)化效率(IPCE)及光電轉(zhuǎn)化效率, 這是由于TiO2/QDs/N719可以吸附更多的量子點(diǎn)和染料。隨著Ag2Se量子點(diǎn)敏化時(shí)間的延長, 光電轉(zhuǎn)化效率先提高后降低, 最高達(dá)到3.97%。Ag2Se量子點(diǎn)在器件中起到了阻擋層作用, 可以促進(jìn)電子傳輸, 抑制電子-空穴復(fù)合。而隨著量子點(diǎn)敏化時(shí)間超過2 h, 電子陷入陷阱的幾率增加, 導(dǎo)致器件的光伏性能下降。

Ag2Se量子點(diǎn); 水相共沉積法; 共敏化; 染料敏化太陽能電池

染料敏化太陽能電池(DSSCs)雖然以低廉的價(jià)格, 環(huán)境友好的特點(diǎn)而備受青睞, 但是發(fā)展至今, 光電轉(zhuǎn)換效率一直難以突破瓶頸[1-4]。近年, 量子點(diǎn)作為一種獨(dú)特的敏化劑, 具有帶隙可調(diào)[5-6]、吸收系數(shù)高[7]和多激子效應(yīng)[8]等優(yōu)點(diǎn), 可代替有機(jī)染料進(jìn)行光陰極或光陽極敏化, 提升光電效率。量子點(diǎn)太陽能電池(QDSSCs)的理論光電轉(zhuǎn)化效率高達(dá)44%, 突破了Shockley-Queisser的31%的效率極限[9], 目前基于液態(tài)電解質(zhì)的QDSSCs最高光電轉(zhuǎn)換效率已達(dá)11.6%[10]。

由于量子點(diǎn)性能優(yōu)異, 一些科研工作者將量子點(diǎn)引入DSSCs中, 進(jìn)行量子點(diǎn)和染料的雙重敏化, 可以進(jìn)一步提高DSSCs的光電轉(zhuǎn)換效率[11-14]。目前量子點(diǎn)主要用連續(xù)離子沉積法(SILAR)、化學(xué)浴沉積(CBD)以及非原位法(包括連接劑輔助吸附和直接吸附)敏化光陽極[15]。SILAR和CBD的劣勢是難以控制量子點(diǎn)的形貌和粒徑, 非原位法則沒有類似的缺點(diǎn)。Ag2Se量子點(diǎn)在可見光和近紅外區(qū)域吸光性能優(yōu)異[16], 有多種合成方法可供選擇, 如溶劑熱法[17]、熱注射法[18]等, 但這些方法需要高溫或者高壓, 合成方法復(fù)雜且要用到有毒試劑。本課題組利用水相共沉積法制備粒徑可控的Ag2Se量子點(diǎn), 該方法操作簡單, 無毒無害。本課題組前期制備了不同粒徑的Ag2Se量子點(diǎn), 采用直接吸附法制備器件[19], 測試電池性能表明Ag2Se量子點(diǎn)作為DSSCs的敏化劑和阻擋層可以有效提高器件的光電性能。本研究在此基礎(chǔ)上, 進(jìn)一步系統(tǒng)地研究了Ag2Se量子點(diǎn)的不同敏化方式和不同敏化時(shí)間對(duì)固態(tài)量子點(diǎn)/染料共敏化太陽能電池的影響, 用光調(diào)制光電流譜、光調(diào)制光電壓譜和電化學(xué)阻抗分析電子傳輸和電荷復(fù)合情況。

1 實(shí)驗(yàn)方法

1.1 實(shí)驗(yàn)試劑

TiO2片子(膜厚12 μm); N719染料(二-四丁銨-雙(異硫氰基)雙(2,2￠-聯(lián)吡啶-4,4￠-二羧基)釕(II)); 硝酸銀 (AgNO3, 99.99%); 氨水 (NH3·H2O, 98%); 聚乙烯吡咯烷酮(PVP, 99.99%); 亞硫酸鈉(Na2SO3, 99.99%); 硒粉(Se, 99.99%); 巰基丙酸(3-MPA, 99.99%); 無水乙醇(C2H5OH, 99.99%)。

1.2 制備Ag2Se量子點(diǎn)

1.2.1 合成Na2SeSO3

將0.8 g單質(zhì)硒粉、3.8 g亞硫酸鈉和50 mL去離子水加入單口瓶中, 在磁力攪拌下于90℃加熱回流反應(yīng)12 h, 得到澄清透明溶液, 避光保存。取少量Na2SeSO3溶液稀釋至2 mmol/L備用。

1.2.2 制備Ag2Se量子點(diǎn)溶液

向三口瓶中依次加入5 mL 4 mmol/L AgNO3溶液, 0.5 mL 3-MPA, 磁力攪拌 10 min, 加入1 mL 1.5 g/L的 PVP 溶液, 用NH3·H2O調(diào)節(jié)溶液pH至10.2~10.5后, 迅速加入5 mL 2 mmol/L的Na2SeSO3溶液, 繼續(xù)攪拌得到棕黃色透明的 Ag2Se 量子點(diǎn)反應(yīng)液。加入異丙醇, 離心分離, 將產(chǎn)物分散到5 mL無水乙醇中, 得到2 mmol/L的Ag2Se量子點(diǎn)溶液。

1.3 組裝DSSCs器件

制備不同敏化方式的光陽極: 在N719染料的乙醇溶液(0.4×10–3mol/L)中浸泡24 h, 標(biāo)記為TiO2/dye; TiO2片子依次在Ag2Se量子點(diǎn)溶液和N719溶液中浸泡1和24 h, 標(biāo)記為TiO2/QDs/dye; TiO2片子依次在N719溶液和量子點(diǎn)溶液中浸泡24和1 h, 標(biāo)記為TiO2/dye/QDs。

制備不同量子點(diǎn)敏化時(shí)間的光陽極: TiO2片子首先在Ag2Se量子點(diǎn)中各浸泡1、2、3、4或5 h, 然后在N719染料中浸泡24 h。

制備電解質(zhì): 將0.4062 g瓊脂糖加入到20 g-甲基吡咯烷酮(NMP)中, 80 ℃水浴恒溫?cái)嚢? h, 再加入0.2582 g I2和0.1361 g LiI, 常溫?cái)嚢? h后得到電解質(zhì)[20-21]。

器件組裝: 所制備的共敏化光陽極均滴加瓊脂糖基聚合物固態(tài)電解質(zhì), 80 ℃烘烤45 min后, 蓋上Pt對(duì)電極, 在干燥箱中65 ℃干燥1.5 h, 完成器件組裝。

1.4 材料和器件的表征

在200 kV進(jìn)行透射電鏡(Tecnai G2 F20 S-Twin)觀測。用UV-1800紫外-可見光光度計(jì)(島津公司)測試光陽極的紫外-可見吸收光譜,=400~1100 nm。采用光譜響應(yīng)測試系統(tǒng)(QE-R)測試入射單色光-電子轉(zhuǎn)化效率(IPCE)。采用CH1604D電化學(xué)工作站和太陽光模擬測量電池的-曲線, 所用光源為氙燈(AM1.5, 100 mW/cm2), 其中模擬光通過標(biāo)準(zhǔn)二極管(Si 1708)校準(zhǔn), 器件的測試面積為0.25 cm2。用可控強(qiáng)度調(diào)制光譜儀進(jìn)行強(qiáng)度調(diào)制光電流譜/光電壓譜(IMPS/IMVS)以及電化學(xué)阻抗譜(EIS)測試。IMPS和IMVS測試條件: 光源為=627 nm的紅光LED, 穩(wěn)態(tài)光的光照強(qiáng)度為10 mW/cm2, 正弦調(diào)制光的振幅為背景光強(qiáng)的10%, 頻率范圍10–1~103Hz。EIS 的測試條件: 交流擾動(dòng)信號(hào)的振幅為10 mV, 偏壓為–0.8 V, 頻率范圍10–1~105Hz。

2 結(jié)果與討論

2.1 Ag2Se量子點(diǎn)的表面形貌分析

圖1(a)所示是水相共沉積法制備的Ag2Se量子點(diǎn)的透射電鏡照片(TEM), 從圖中可以看出, Ag2Se量子點(diǎn)顆粒均勻、分散性好、團(tuán)聚現(xiàn)象較少, 具有規(guī)則統(tǒng)一的球形顆粒形貌。圖1(b)是200個(gè)Ag2Se量子點(diǎn)的粒徑統(tǒng)計(jì)圖, 從圖中可以看出粒徑主要分布在6~15 nm, 集中在~8 nm, 與平均尺寸8.51 nm相吻合。高分辨透射電鏡照片(圖1(c)和(d))顯示了Ag2Se量子點(diǎn)的晶格條紋, 晶面間距為0.24 nm, 對(duì)應(yīng)-Ag2Se相的(013)面[22-23]。

圖2(a)是Ag2Se量子點(diǎn)分散在無水乙醇中的紫外-可見光譜圖, (b)是相應(yīng)的Tauc圖譜, 計(jì)算得到Ag2Se量子點(diǎn)(8.51 nm)的禁帶寬度為1.65 eV, 測試結(jié)果與粒徑大于10 nm的Ag2Se塊體材料(0.07~ 0.15 eV)不同, 這是由于Ag2Se量子點(diǎn)禁帶寬度受到了量子點(diǎn)粒徑大小的影響[24-26]。

圖1 Ag2Se量子點(diǎn)的(a)透射電鏡照片, (b)粒徑分布直方圖, (c)高分辨透射電鏡照片和(d)放大高分辨透射電鏡照片

圖2 (a) Ag2Se量子點(diǎn)乙醇溶液的紫外-可見光譜圖; (b)相應(yīng)的Tauc圖譜

2.2 不同敏化方式的DSSCs表征

優(yōu)先染料敏化還是優(yōu)先量子點(diǎn)敏化直接改變TiO2光陽極的光譜響應(yīng), 進(jìn)而影響器件的光電效率。圖3(a)是不同敏化方式光陽極的紫外-可見光吸收譜圖。由圖可以看出, TiO2/QDs/dye的吸收強(qiáng)度優(yōu)于TiO2/dye和TiO2/dye/QDs, 說明依次用量子點(diǎn)和染料吸附的光陽極有利于增強(qiáng)器件對(duì)太陽光的吸收, 并且TiO2/dye比TiO2/dye/QDs著色更深, 這是因?yàn)镹719中的COO–和COOH以氫鍵和二齒橋接鍵合到TiO2[27], 當(dāng)TiO2薄膜吸附了足夠的N719再浸泡到Ag2Se量子點(diǎn)的乙醇溶液中會(huì)發(fā)生脫附, 留下空位可以吸附表面帶有巰基[28-29]的Ag2Se量子點(diǎn)。由于Ag2Se量子點(diǎn)對(duì)光的吸收強(qiáng)度低于N719染料, 所以TiO2/dye/QDs光陽極的光譜吸收強(qiáng)度弱于TiO2/dye的光譜吸收強(qiáng)度; 而對(duì)于TiO2/QDs/dye光陽極, Ag2Se量子點(diǎn)的粒徑小于TiO2, 導(dǎo)致光陽極比表面積增加, 由于染料可以吸附于TiO2以及Ag2Se量 子點(diǎn)上, 所以染料的吸附量比在單純的TiO2光陽極上更多, 促使TiO2/QDs/dye具有更優(yōu)良的光譜吸收強(qiáng)度[30]。

圖3(b)是不同Ag2Se量子點(diǎn)敏化方式的太陽能電池的-特性曲線, 由此得到開路電壓oc, 短路電流密度sc, 填充因子, 光電轉(zhuǎn)換效率(表1)。TiO2/QDs/dye的oc明顯高于TiO2/dye, 從0.69 V提高到0.74 V,sc從8.78 mA·cm–2提高到9.18 mA·cm–2,由2.96%提升到3.59%, 說明量子點(diǎn)先于染料吸附的光陽極有助于提升器件的光電轉(zhuǎn)換效率。而對(duì)于TiO2/dye/QDs, 由于Ag2Se量子點(diǎn)溶液使光陽極上的N719染料脫附, 短路電流降低, 所以TiO2/dye/ QDs器件的光電轉(zhuǎn)換效率較TiO2/dye低。

圖4是不同Ag2Se量子點(diǎn)敏化方式的太陽能電池IPCE曲線, 從圖中可以發(fā)現(xiàn)TiO2/QDs/dye器件在波長400~750 nm波長范圍內(nèi)均高于TiO2/dye, 進(jìn)一步證明Ag2Se量子點(diǎn)有利于提高器件的光電轉(zhuǎn)化性能, 從而擁有較高的短路電流; 而TiO2/dye/QDs器件的IPCE最低, 這是由于N719脫附導(dǎo)致器件吸光性能減弱,sc降低。

圖3 (a)不同敏化方式光陽極的紫外-可見吸收光譜分析, 插圖為光陽極照片; (b)不同敏化方式DSSCs的J-V曲線

表1 不同敏化方式的光電參數(shù)

圖4 不同敏化方式的太陽能電池IPCE曲線

2.3 Ag2Se量子點(diǎn)不同敏化時(shí)間的固態(tài)基量子點(diǎn)-染料共敏化太陽能電池

TiO2光陽極在量子點(diǎn)溶液中浸泡的時(shí)間直接影響量子點(diǎn)吸附密度, 進(jìn)而影響器件的光伏性能。圖5(a)是Ag2Se量子點(diǎn)和染料共敏化固態(tài)基太陽能電池的結(jié)構(gòu)示意圖, 其中量子點(diǎn)和染料可一起作為光吸收劑。圖5(b)是器件各組成部分的能帶圖, 由文獻(xiàn)[13]可知電解質(zhì)和N719染料的能帶數(shù)據(jù), 根據(jù)圖2(b)的吸收光譜Tauc數(shù)據(jù)可計(jì)算Ag2Se量子點(diǎn)禁帶寬度是1.65 eV, 導(dǎo)帶位置為-2.5 eV[19], 由此推算其價(jià)帶位置為-4.15 eV, 高于TiO2導(dǎo)帶, 這有利于Ag2Se量子點(diǎn)激發(fā)的電子傳輸?shù)絋iO2, 同時(shí)能有效阻 止TiO2中電子與電解質(zhì)產(chǎn)生復(fù)合, 從而提升器件 的oc。

Ag2Se量子點(diǎn)的敏化時(shí)間直接影響TiO2光陽極吸附密度, 從而導(dǎo)致吸收光譜的變化, 圖6(a)是TiO2/QDs、TiO2/dye、TiO2/QDs/dye的紫外-可見吸收光譜圖, 結(jié)果表明TiO2/QDs/dye光陽極有利于對(duì)太陽能譜的吸收。圖6(b)是TiO2光陽極在Ag2Se量子點(diǎn)中浸泡1、2、3、4或5 h的紫外-可見吸收光譜圖, 隨著TiO2光陽極在Ag2Se量子點(diǎn)中浸泡時(shí)間的延長, TiO2光陽極上吸附的Ag2Se量子點(diǎn)密度增加, 導(dǎo)致吸收光譜的強(qiáng)度逐漸增強(qiáng)。

圖5 固態(tài)基Ag2Se量子點(diǎn)和染料共敏化太陽能電池的(a)結(jié)構(gòu)示意圖和(b)能帶機(jī)理圖

圖6 (a)Ag2Se量子點(diǎn)敏化、N719敏化以及Ag2Se/N719共敏化光陽極的紫外-可見吸收光譜圖; (b)Ag2Se量子點(diǎn)敏化不同時(shí)間的光陽極的紫外-可見吸收光譜圖

圖7是純Ag2Se量子點(diǎn)敏化太陽能電池和量子點(diǎn)不同敏化時(shí)間的共敏化太陽能電池的-曲線, 其性能參數(shù)如表2所示。結(jié)果表明純Ag2Se量子點(diǎn)敏化器件的相當(dāng)?shù)? 這是因?yàn)镮–/I3–電解質(zhì)容易引起量子點(diǎn)的光降解和腐蝕, 不適用于量子點(diǎn)敏化太陽能電池[31-33]。但Ag2Se量子點(diǎn)引入DSSCs后,從2.96%提高到3.97%。一方面Ag2Se量子點(diǎn)敏化時(shí)間的延長, TiO2光陽極吸附的Ag2Se量子點(diǎn)的負(fù)載量增加, 導(dǎo)致光生電子增加; 另一方面Ag2Se量子點(diǎn)作為阻擋層可以增強(qiáng)電子傳輸性能, 抑制電子空穴的復(fù)合, 有效控制器件的暗反應(yīng), 使sc增大[34], 從8.78 mA?cm–2提高到9.53 mA?cm–2, 光電性能得到明顯的提升。但當(dāng)量子點(diǎn)敏化時(shí)間進(jìn)一步延長時(shí), 隨著量子點(diǎn)密度增大, 電子的復(fù)合中心也同時(shí)增多, 導(dǎo)致電子陷入陷阱的幾率增加,sc慢慢降低[35]。由于電解質(zhì)相同, 到多孔膜的滲透性能相同, 所以變化不大[21]。此外, 器件的oc取決于電解質(zhì)氧化還原電位和半導(dǎo)體的費(fèi)米能級(jí), 但是Ag2Se量子點(diǎn)作為阻擋層與TiO2親密接觸, 引起半導(dǎo)體費(fèi)米能級(jí)變化, 相比于純?nèi)玖厦艋骷c得到明顯提升[36-37]。

圖7 純Ag2Se量子點(diǎn)敏化太陽能電池和Ag2Se量子點(diǎn)敏化不同時(shí)間的共敏化太陽能電池J-V曲線

表2 Ag2Se量子點(diǎn)敏化不同時(shí)間的共敏化太陽能電池光電參數(shù)

圖8(a)是Ag2Se量子點(diǎn)敏化不同時(shí)間的共敏化太陽能電池器件的Nyguist交流阻抗圖譜, 圖中給出了等效電路圖以及依據(jù)該等效電路做的擬合曲線(ZSimDemo)。DSSCs的奈奎斯特電化學(xué)阻抗圖譜由高頻段、中頻段和低頻段的三個(gè)半圓弧組成。高頻段的阻抗代表電池中Pt對(duì)電極與電解質(zhì)溶液界面間的氧化還原反應(yīng)電阻(1); 中頻段的阻抗代表電池中TiO2/Dye(Ag2Se)/電解質(zhì)三相界面處的復(fù)合電阻(2); 低頻段的阻抗代表離子在電解質(zhì)溶液中的擴(kuò)散阻抗(3)。由于使用的電解質(zhì)和Pt對(duì)電極都相同, 所以1和3大致相同[38]。如圖8(b)所示, 引入Ag2Se量子點(diǎn)阻擋層后,2明顯增大, 說明電子的復(fù)合受到抑制, 隨著Ag2Se量子點(diǎn)敏化時(shí)間的延長,2先升高后降低。這是因?yàn)锳g2Se量子點(diǎn)阻擋層阻止了注入的電子與電解質(zhì)中I3–的復(fù)合[39]; 但是隨著Ag2Se量子點(diǎn)敏化時(shí)間的進(jìn)一步延長, 光陽極量子點(diǎn)吸附量也逐漸增加, 而增加的量子點(diǎn)會(huì)導(dǎo)致電子更易于陷入陷阱, 使復(fù)合電阻逐漸降低。oc變化趨勢本應(yīng)該一致, 但是Ag2Se量子點(diǎn)作為TiO2阻擋層使TiO2費(fèi)米能級(jí)發(fā)生變化[36-37], 所以即使器件復(fù)合電阻2減小, 但oc變化不明顯。最終, Ag2Se量子點(diǎn)敏化時(shí)間為2 h時(shí), 得到最大oc為0.75 V,為0.55, 此時(shí)器件的最佳。

圖8 (a) Ag2Se量子點(diǎn)敏化不同時(shí)間的共敏化太陽能電池器件的交流阻抗圖譜, 插圖為等效電路圖; (b) R2隨Ag2Se量子點(diǎn)敏化時(shí)間的變化曲線

圖9 Ag2Se量子點(diǎn)敏化不同時(shí)間的共敏化太陽能電池器件的(a) IMPS/VS和(b)IMVS圖譜

表3 Ag2Se量子點(diǎn)敏化不同時(shí)間的共敏化太陽能電池器件的IMPS/VS動(dòng)力學(xué)參數(shù)

3 結(jié)論

用水相共沉積法合成平均粒徑為8.51 nm的Ag2Se量子點(diǎn), 研究了TiO2光陽極不同敏化方式的染料-量子點(diǎn)共敏化固態(tài)太陽能電池, TiO2/Ag2Se/ dye器件比TiO2/dye/Ag2Se具有更加優(yōu)異的光電性能; 隨著Ag2Se量子點(diǎn)敏化時(shí)間的延長, 器件光電轉(zhuǎn)換效率先升高后降低, 當(dāng)TiO2光陽極在Ag2Se量子點(diǎn)中浸泡2 h時(shí), 光電效率最佳, 達(dá)到3.97%, 短路電流為9.53 mA·cm–2, 開路電壓為0.75 V。TiO2光陽極在Ag2Se量子點(diǎn)中敏化時(shí)間較短時(shí), 一方面Ag2Se量子點(diǎn)可以作為吸光層提高光電子產(chǎn)率, 增大器件短路電流; 另一方面Ag2Se量子點(diǎn)作為阻擋層可以有效抑制電子與電解質(zhì)中I3–復(fù)合, 有利于提升器件的性能。而隨著Ag2Se量子點(diǎn)敏化時(shí)間進(jìn)一步延長, 電子陷入陷阱的幾率增大, 導(dǎo)致短路電流密度下降。

[1] XIE Y S, TANG Y Y, WU W J,. Porphyrin cosensitization for a photovoltaic efficiency of 11.5%: a record for non-ruthenium solar cells based on iodine electrolyte.., 2015, 137(44): 14055–14058.

[2] MATHEW S, YELLA A, GAO P,. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers.., 2014, 6(3): 242–247.

[3] OZAWA H, YU O, ARAKAWA H. Dependence of the efficiency improvement of black-dye based dye-sensitized solar cells on alkyl chain length of quaternary ammonium cations in electrolyte solutions.., 2014, 15(6): 1201–1206.

[4] KAKIAGE K, AOYAMA Y, YANO T,. Fabrication of a high-performance dye-sensitized solar cell with 12.8% conversion efficiency using organic silyl-anchor dyes.., 2015, 51(29): 6315–6317.

[5] YU W W, PENG X G. Formation of high quality CdS and other II–VI semiconductor nanocrystals in noncoordinating solvents: tunable reactivity of monomers.., 2002, 41(13): 2368–2371.

[6] SARMA D D, NAG A, SANTRA P K,. Origin of the enhanced photoluminescence from semiconductor CdSeS nanocrystals., 2010, 1(14): 2149–2153.

[7] SEOL M, KIM H, TAK Y,. Novel nanowire array based highly efficient quantum dot sensitized solar cell.., 2010, 46(30): 5521–5523.

[8] ELLINGSON R J, BEARD M C,JOHNSON J C,.Highly efficient multiple exciton generation in colloidal PbSe and PbS quantum dots., 2005, 5(5): 865–871.

[9] SCHALLER R D, AGRANOVICH V M, KLIMOV V I. High-efficiency carrier multiplication through direct photogeneration of multi-excitonsvirtual single-exciton states., 2005, 1(3): 189–194.

[10] DU J, DU Z, HU J S,. Zn–Cu–In–Se quantum dot solar cells with a certified power conversion efficiency of 11.6%.., 2016, 138(12): 4201–4209.

[11] JI G, LIU Z, GUAN D,. Ag2S quantum dots and N3 dye co-sensitized TiO2, nanotube arrays for a solar cell.., 2013, 282(10): 695–699.

[12] LIU Y, WANG J. Co-sensitization of TiO2, by PbS quantum dots and dye N719 in dye-sensitized solar cells., 2010, 518(24): E54–E56.

[13] YANG Y, GAO J, ZHANG Z,. Black phosphorus based photocathodes in wide band bifacial dye-sensitized solar cells.., 2016, 28(40): 8937–8944.

[14] GUO X Y, GAO J, ZHANG Z,. Highly efficient interfacial layer using SILAR derived Ag2S quantum dots for solid-state bifacial dye-sensitized solar., 2017, 5: 320–330.

[15] GIMENEZ S, LANA-VILLARREAL T, GOMEZ R,. Determination of limiting factors of photovoltaic efficiency in quantum dot sensitized solar cells: correlation between cell performance and structural properties.., 2010, 108(6): 064310–1–7.

[16] SCHOEN D T, XIE C, CUI Y. Electrical switching and phase transformation in silver selenide nanowires.., 2007, 129(14): 4116–4117.

[17] SAHU A, BRAGA D, WASER O,. Solid-phase flexibility in Ag2Se semiconductor nanocrystals.., 2014, 14(1): 115–121.

[18] ZHU C N, JIANG P, ZHANG Z L,. Ag2Se quantum dots with tunable emission in the second near-infrared window., 2013, 5(4): 1186–1189.

[19] ZHANG Z, YANG Y, GAO J,. Highly efficient Ag2Se quantum dots blocking layer for solid-state dye-sensitized solar cells: size effects on device performances., 2018, 7: 27–36.

[20] YANG Y, YI P, ZHOU C,Magnetic field processed solid- state dye-sensitized solar cells with nickel oxide modified agarose electrolyte., 2013, 243(6): 919–924.

[21] YANG Y, ZHANG Z, GAO J,. Metal-organic materials as efficient additives in polymer electrolytes for quasi-solid-state dye-sensitized solar cells., 2017, 726: 1286–1294.

[22] TIAN Q, DENG D, ZHANG Z,. Facile synthesis of Ag2Se quantum dots and their application in dye/Ag2Se co-sensitized solar cells.2017, 52(20): 12131–12140.

[23] GU Y P, CUI R, ZHANG Z L,. Ultrasmall near-infrared Ag2Se quantum dots with tunable fluorescence forimaging.., 2012, 134(1): 79–82.

[24] PEJOVA B, NAJDOSKI M, GROZDANOV I,. Chemical bath deposition of nanocrystalline (111) textured Ag2Se thin films., 2000, 43(5/6): 269–273.

[25] ANTHONY, PHILIP S. Synthesis of Ag2S and Ag2Se nanoparticles in self assembled block copolymer micelles and nano-arrays fabrication., 2009, 63(9): 773–776.

[26] SIBIYA P N, MOLOTO M J. Effect of precursor concentration and pH on the shape and size of starch capped silver selenide (Ag2Se) nanoparticles., 2014, 11(11): 577–588.

[27] LEE K E, GOMEZ M A, ELOUATIK S,. Further understanding of the adsorption mechanism of N719 sensitizer on anatase TiO2films for DSSC applications using vibrational spectroscopy and confocal Raman imaging., 2010, 26(12): 9575– 9583.

[28] LUO J, WEI H, HUANG Q,. Highly efficient core–shell CuInS–Mn doped CdS quantum dot sensitized solar cells.., 2013, 49(37): 3881–3883.

[29] HU X, ZHANG Q X, HUANG X M,. Aqueous colloidal CuInS2for quantum dot sensitized solar cells.., 2011, 21(40): 15903–15905.

[30] CUI C, QIU Y W, ZHAO J H,A comparative study on the quantum-dot-sensitized, dye-sensitized and co-sensitized solar cells based on hollow spheres embedded porous TiO2photoanodes., 2015, 173: 551–558.

[31] REN F M, LI S J, HE C L. Electrolyte for quantum dot-sensitized solar cells assessed with cyclic voltammetry., 2015, 58(6): 490–495.

[32] SHALOM M, DOR S, RUHLE S,.Core CdS quantum dot/shell mesoporous solar cells with improved stability and efficiency using an amorphous TiO2coating., 2009, 11(9): 3895–3898.

[33] SERO I M, BISQUERT J. Breakthroughs in the development of semiconductor-sensitized solar cells., 2010, 1(20): 3046–3052.

[34] LAN Z, WU W X, ZHANG S,. An efficient method to prepare high-performance dye-sensitized photoelectrodes using ordered TiO2nanotube arrays and TiO2quantum dot blocking layers., 2016, 20(10): 2643–2650.

[35] LI J, LI Z, WANG S,. Great improvement of photoelectric property from co-sensitization of TiO2electrodes with CdS quantum dots and dye N719 in dye-sensitized solar cells.., 2013, 48(7): 2566–2570.

[36] XU B, WU J H, ZHANG X K,. The influence of blocking layer on the photovoltaic properties of dye-sensitized solar cells., 2008, 39: 1703–1709.

[37] LELII C, BAWENDI M G, BIAGINI P,. Enhanced photovoltaic performance with co-sensitization of quantum dots and an organic dye in dye-sensitized solar cells., 2014, 2: 18375–18382.

[38] GAO J, YANG Y, ZHANG Z,. Bifacial quasi-solid-state dye-sensitized solar cells with poly (vinyl pyrrolidone)/polyaniline transparent counter electrode., 2016, 26: 123–130.

[39] ELBOHY H, THAPA A, POUDEL P,Vanadium oxide as new charge recombination blocking layer for high efficiency dye-sensitizedsolar cells., 2015, 13: 368–375.

[40] YANG Y, WANG W. Effects of incorporating PbS quantum dots in perovskite solar cells based on CH3NH3PbI3.,2015, 293: 577–584.

[41] LAGEMAAT J V D, FRANK A J. Nonthermalized electron transport in dye-sensitized nanocrystalline TiO2films: transient photocurrent and random-walk modeling studies., 2001, 105(45): 11194–11205.

[42] OEKERMANN T,ZHANG D, YOSHIDA T,.Electron transport and back reaction in nanocrystalline TiO2films prepared by hydrothermal crystallization., 2004, 108(7): 2227–2235.

[43] ZHU K, NEALE N R, MIEDANER A,Enhanced charge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO2nanotubes arrays.., 2007, 7(1): 69–74.

Photovoltaic Performance of Ag2Se Quantum Dots Co-sensitized Solid-state Dye-sensitized Solar Cells

YANG Ying1,2,3, PAN De-Qun1,2,3, ZHANG Zheng1,2,3, CHEN Tian1,2,3, HAN Xiao-Min1, ZHANG Li-Song1, GUO Xue-Yi1,2,3

(1. School of Metallurgy and Environment, Central South University, Changsha 410083, China; 2. Hunan Key Laboratory of Nonferrous Metal Resources Recycling, Changsha 410083, China; 3. Hunan Engineering Research Center of Nonferrous Metal Resources Recycling, Changsha 410083, China)

Ag2Se quantum dots (QDs) was synthesized by co-deposition method which was further applied as co-sensitizer in solid-state dye-sensitized solar cells (DSSCs). The effects of different sensitization methods of Ag2Se QDs (TiO2/N719/QDs, TiO2/QDs/N719) and sensitization time (0-5 h) on the performance of QDs/dye co-sensitized solar cells were studied. Structure and optical properties of Ag2Se QDs were characterized by transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV-Vis). Furthermore, the transmission of charge carriers of solar cell devices was characterized by photo-modulated photocurrent/voltage spectrum (IMPS/VS) and electrochemical impedance spectra (EIS). It was found that the device with TiO2/QDs/N719 showed higher incident photon-to-current efficiency (IPCE) and photoelectric efficiency than those of TiO2/N719/QDs, which was due to the fact that TiO2/QDs/N719 photoanode adsorbed more QDs and dyes. With the extension of Ag2Se QDs sensitization time, the photovoltaic properties of DSSCs firstly ascended and then descended, achieving the highest photoelectric conversion efficiency 3.97%. The incorporation of Ag2Se QDs could effectively promote the electron transport and inhibit the electron-hole recombination, which benefited from a blocking layer that QDs served in device. As sensitization time prolonged over 2 h, the photovoltaic performances of device deteriorated, which was attributed to the augmented trap sites in Ag2Se QDs layer.

Ag2Se quantum dots; co-deposition method; co-sensitized; dye-sensitized solar cell

TM914

A

1000-324X(2019)02-0137-08

10.15541/jim20180233

2018-05-17;

2018-09-20

國家自然科學(xué)基金(61774169); 中南大學(xué)創(chuàng)新驅(qū)動(dòng)計(jì)劃項(xiàng)目(2016CX022); 留學(xué)回國基金資助以及湖南省自然科學(xué)基金(2016JJ3140); 中南大學(xué)研究生創(chuàng)新項(xiàng)目(1053320170116, 1053320170565); 中南大學(xué)本科生創(chuàng)新項(xiàng)目(cx20170271, 201710533300) National Natural Science Foundation of China (61774169); Third Innovation Driven Project of Central South University (2016CX022); Scientific Research Foundation for the Returned Overseas Chinese Scholar, Natural Science Foundation of Hunan (2016JJ3140); The Projects of Innovation for Graduate Student of Central South University (1053320170116, 1053320170565); The Projects of Innovation for Undergraduate Student of Central South University (cx20170271, 201710533300)

楊英(1980–), 女, 副教授. E-mail: muyicaoyang@csu.edu.cn

郭學(xué)益, 教授. E-mail: xyguo@csu.edu.cn