Preparation of Advanced Window Layer for Chalcopyrite Thin Film Photovoltaic Devices

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The photovoltaic power system has received considerable attention to solve the environmental problems in the worldwide scale. It is very important to develop the solar cells with low cost and high efficiency. The thin film of chalcopyrite Cu (In, Ga)Se_2 is one of the potential candidates for high-efficiency solar cells, because its efficiency is over 17%. For improvement in Cu(In, Ga)Se_2 based photovoltaic device performance, the lattice matching window material to Cu(In, Ga)Se_2 must be developed and the window absorption loss should be small. The (0001) plane of the wurtzite (Cd, Zn)S alloy system gives the best lattice matching to the (112) plane of Cu (In, Ga)Se_2 over the whole range of [Ga]/([In]+[Ga]) ratio. In this study, my goal is the preparation and characterization of (Cd, Zn)S thin films by chemical bath deposition. I propose the process for preparation of (Cd, Zn)S thin films that all the reactants are mixed after heating to 80ﾟC and the ammonia used as a complexing agent is simultaneously added. The incorporation of Zn into the film and the band gap of (Cd, Zn)S thin films were controlled by varing the amounts of ammonia. Thin films of (Cd, Zn)S were prepared by the improved process which was optimized with the amounts of ammonia playing an important role. X-ray diffraction peaks for the deposited thin films were assigned to diffraction lines from wurizite (Cd, Zn)S.The [Zn]/([Cd]+[Zn]) ratio and the band gaps in the thin films could be controlled by varying the mixture ratio of CdI_2 and ZnI_2 solutions used as reactants. The variation of band gaps yielded the bowing parameter of 0.724 eV.Cu(In, Ga)Se_2 solar cells with the advanced window layer (Cd, Zn)S were prepared. This device showed an open curcuit voltage of 304mV, a short curcuit current of 37.3mA/cm^2, a fill factor of 0.43 3 and an efficiency of 4.91%. Therefore, I proved that the replacement of CdS with (Cd, Zn)S led to the increase in short curcuit current of solar cell.