|dc.description.abstract||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.