High-efficiency Cd-free CIGSS thin-film solar cells with solution grown zinc compound buffer layers

Zn-compounds Zn(X,OH) (X = S,Se) buffer layers have been deposited by chemi cal bath (CBD) process on Cu(In,Ga)(S,Se)(2) (CIGSS) with the aim of develo ping Cd-free CIGSS-based devices. The films are produced in alkaline aqueou s solution containing ZnSO4, ammonia NH3 and XC(NH2)(2). Optimum deposition conditions were established. The temperature (T-sub) of the chemical bath is found to be critical for the device quality. The thickness and good surf ace coverage were controlled by XPS-UPS photoemission spectroscopy. SEM stu dy showed that the growth of ZnSe nuclei on CIGSS proceeds in lateral direc tion. Once the surface is covered the growth takes place in vertical direct ion. The ZnSe clusters grow in size and their elongated shapes cover the CI GSS surface. High efficiency of over 13% was obtained for both CIGSS/Zn(S,O H) and CIGSS/Zn(Se,OH)-based solar cells. Solar cells with CIGSS/Zn(Se,OH)( x)/ZnO/MgF2 structure show an active area efficiency up to 15.7%. Using Zn( Se,OH) buffer layer, efficiency of 11.7% was achieved with a 20 cm(2) apert ure-area monolithic minimodule. (C) 2001 Elsevier Science B.V. All rights r eserved.