Study On The Fabrication Of CuInSe₂Thin Films Via Electrochemical Deposition And Their Photovoltaic Properties

Compared with most solar cell absorber layers, the absorption spectrum ofsemiconductor CuInSe2（CIS） with a direct band gap of about1.1eV, matchesbetter with the solar spectrum, indicates that CIS is a nearly ideal absorber for thinfilm solar cells. CIS thin films are deposited by vacuum technology, which requiresexorbitant equipments and have a low raw materials utilization rate. And theproduction cost has not reached the expected value. By the electrochemicaldeposition, the materials utilization rate can reach up to95%. In comparison withCIS thin films prepared by vacuum technology, the electrochemical deposition hasemerged as an alternative cost-efficient method. In general, the method for CISfabrication via electrochemical deposition is that one-step electrochemicaldeposition that provides all the components into the same electrolyte with a singlestep, then composition of the CIS precursor film is modified by high vacuumtechnology. There are few reports on the synthesis of CIS fabrication by aselenization technique in toxic H2Se vapor. In view of the above, we developed agreen process for preparation of high quality CIS thin films. The effects ofelectrochemical deposition mechanism, annealing process, heat treatment time andtemperature were investigated systematically. Furthermore, superstrate solar cellsbased on CIS thin films was fabricated by this process, the structure and property ofsolar cells have been investigated. The main research results obtained as follows:1. CIS thin films were synthesized by electrochemical deposition.The process of Cu-Se, In-Se compound impurity phases emerging, and the causeof Cu-rich, Cu-poor CIS thin films appearing under different deposition potentialwere studied by Cyclic Voltammetry. The electrochemical deposition mechanism ofCIS thin films was explored preliminarily: Cu²⁺and H₂SeO₃were first reduced toCu₃Se₂, then In³⁺was deposited via the induced co-deposition mechanism. Theresults showed that the structure and morphology of CIS thin films were determined bydeposition potential and Se-Cu proportion （α） in the electrolyte solution. The optimalcondition could improve the quality of CIS thin films. CIS thin films weredeposited at-1V in electrolyte solution with α=3.2. The quality of CIS thin films were improved by rapid selenide annealing. The effect of annealing rates and atmosphere were investigated. The results showedthat the selenization and rapid annealing technique could improve the crystallinityof CIS, avoid the formation of crack and impurity phase, and result in slightlyCu-poor CIS thin films. Then the effects of heat treatment time and temperaturehave been studied systematically. High quality CIS thin films were fabricated at350°C for60min.3. Combined with these route, the superstrate solar cells based CIS on thin filmswere fabricated successfully. The structure and property of In₂Se₃（IS） buffer layer werestudied. The results showed that the calculated value of the band gaps of the IS filmdecreased to1.84eV after annealing. The stacked thin films composed of IS andCIS layers were grown on ITO substrates after annealing at350°C, the stackedstructure of ITO/IS/CIS was still keep emerging clearly. The superstrate solar cellsbased on this stacked thin films show a higher open circuit voltage of0.31V and apreliminary conversion efficiency of1.9%.