溶劑熱法製備Cu-In-Zn-S薄膜及其光電化學性質

Photoelectrochemical performance of Cu-In-Zn-S thin films prepared by solvothermal process

李奕樺(I-Hua Li)

指導教授 ： 李岱洲

國立中央大學/工學院/化學工程與材料工程學系/碩士(2015年)

摘要

本研究利用溶劑熱法搭配不同的基材和四元成份的比例來製備Cu-In-Zn-S光觸媒薄膜，在固定Cu-Zn-S比例前提下，改變In的比例，製備出n和p型的光觸媒薄膜，並分析薄膜之光電化學性質及半導體型態。從實驗結果可以發現，使用Cu (NO3)2　+ Zn(NO3)6H2O + In(NO3)•xH2O系列的前驅物且溶劑為水時，所製備的薄膜為CuIn5S8相和Cu2In2ZnS5相之混相；而在CuSO45H2O + InCl34H2O + ZnCl2系列，溶劑為無水乙醇並且使用APS改質之FTO玻璃為基材，此時製備出來的相為Cu2In2ZnS5相，藉由吸收光譜可以推測直接推測能隙為1.69~1.95 eV。
使用APS改質的FTO玻璃所形成之CIZS薄膜品質良好，且薄膜與基材的附著力優於未改質 FTO玻璃或使用MPS改質之CIZS薄膜。從電化學量測結果得知成功製備出n-type和p-type的CIZS薄膜。但在電化學測量後CIZS薄膜還是會脫落造成基材裸露，代表薄膜附著性依然不佳，因此換成有相似成份(In、S)的AIS(AgInS2)為基材，藉此增加CIZS 與基材的附著性，卻因而發現會有些許銅的硫化物(Cu31S16)存在薄膜中。
當使用FTO(APS)為基材時，測得在負偏壓下會有光電流值出現，但其光電流值偏低，可能是因附著性不加造成基材裸露，使得暗電流一直上升。然而，改用AIS(AgInS2)當作基材、從背面照光時(AIS往CIZS方向)，發現相對於其他基材上會有較高的光電流值產生，並且有類似p-n junction的現象發生。為了增加光電流值產生，在AIS(AgInS2)薄膜上鍍上一層金之後再成長CIZS薄膜，藉此形成Z-scheme結構的特性，金觸媒在兩層薄膜之間當作電荷轉移之媒介，以增強電荷轉移的效果，使得在背面照光時保有n型和p型半導體的特性，並且光電流有明顯的增加，於負偏壓(-1.5V vs. SCE)光電流值約為0.5 mA/cm2。

關鍵字

溶劑熱法

並列摘要

In this study, we prepared Cu-In-Zn-S (CIZS) photocatalyst thin films using solvothermal method, in which different substrate modifications, anions of precursors, and molar ratios of the precursors were varied. It was found that n-type and p-type semiconductor materials can be obtained by changing the [In]/[Zn] molar ratios. To our best knowledge, it is the first report of tuning the CIZS conduction type as a function of relative composition. The morphology and photoelectrochemical (PEC) properties of thin films were subsequently studied. Results showed that thin films, utilizing NO3- as precursors and DI water as solvents, were the mixtures of CuIn5S8 and Cu2In2ZnS5; in contrast thin films on 3-Aminopropyltriethoxysilane (APS)-modified FTO-coated glass substrate utilizing Cl- and CuSO4 as precursors and ethanol as solvents, were single-phase Cu2In2ZnS5. The direct energy band gap determined from absorption spectrum was in the range of 1.69 to 1.95 eV.
Although the adhesion of the CIZS films on APS-modified substrate was improving, compared to the ones on bared and on MPS-modified FTO-coated glass substrates, the CIZS films peeled off after PEC measurement in aqueous solution. To mitigate this problem, AgInS2 (AIS) was used as the buffer at the CIZS-substrate interface. It is expected that, due to similar elements (In, S) presented in AIS and good adhesion of AIS on FTO-coated substrate, he attachment of CIZS films onto the AIS/FTO substrate can be greatly improved. Nevertheless, some CuS (Cu31S16) remained in CIZS films.
Regarding the photoelectrochemical properties of CIZS films as the photoanode, low photocurrent density was observed for CIZS on APS-modified FTO, perhaps due to the poor interface at the CIZS-substrate interface. In contrast, photo-electrode consisting of CIZS/AIS/FTO layered structure exhibited a better photoactivity, especially when the light was irradiated from the back side (from the glass window), similar to the p-n heterojunction reported in the literature.
In a parallel experiment, a layer of Au was coated on the AIS/FTO, before deposition of CIZS. In fact Au played an important role as a storage and recombination center for electrons, in this CIZS/Au/AIS/FTO Z-scheme structure. A photocurrent density of 0.5 mA /cm2 (under a bias of -1.5 V vs. SCE) was obtained. This study demonstrated that employing suitable synthesis strategy opened a new possibility of preparing thin film electrode from solution process. These semiconductor thin film can be further incorporated into various layered structure for photoelectrochemical application.

並列關鍵字

solvothermal ； CIZS(Cu-In-Zn-S) ； PEC

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