Vacuum and Liquid-Phase Processing of ZnSe Buffer-Layer for Chalcopyrite Absorber Based Photovoltaic Technology

摘要

ZnSe thin films were processed in-vacuum by EBD and in-solution by CBD for comparative studies of CdS-buffer replacement of ZnO/CdS/Cu(In, Ga)Se-2/Mo/glass solar-cells. ZnSe films deposited by EBD, at e-beam energies 11keV, on polycrystalline CuGaSe2, at 400 degrees C, were microcrystalline, with average grain-sizes 100nm, and (111)zinc-blende(ZB)-structure. The films exhibited compressive mismatch-stresses sigma = -0.9 GPa. The absorption coefficient alpha = 6.2 x 10(3) cm(-1) and the energy band-gap E-g = 2.69eV indicated optical transparency suitable for buffer/solar-absorber configurations. In CBD, zinc-sulfate_(ZnSO4) solution with selenourea_(SeC(NH2)(2)), ammonia_(NH3), hydrazine_(NH2NH2), and sodium-sulfite_(Na2SO3) were processed at solution-bath temperature 70 degrees C. The growth-rates of ZnSe on glass_(1.2nm/min), epitaxial_CuGaSe2/GaAs(001)_(7.4nm/min), and polycrystalline_Cu(In,Ga)Se-2/Mo/glass_(17.6nm/min) were strongly facilitated by substrate order, orientation, and conductivity. Mismatch-stresses switched from compressive sigma = -0.5GPa of ZnSe_on_epitaxial_CuGaSe2/GaAs(001) to tensile sigma = 1.1-1.9GPa of ZnSe_on_polycrystalline_Cu(In,Ga)Se-2/Mo/glass. Film crystallinity was improved by post-growth annealing (300 degrees C,2h,Ar/N-2). The energy band-gap E-g = 2.73-2.87eV was broadened with the increase of annealing-time. ZnSe films were deposited by CBD on polycrystalline Cu(In,Ga)Se-2 with (101)wurtzite(WZ)-structure. Following process-optimization, high quality ultra-thin films with (ZB)-structure were produced. The quality assessment of ZnSe films processed by cost-effective, easy-applicable, fast-rate, large-area, moderate-temperature CBD competes with that of EBD processed films and opens the perspective for strain-free CIGS TFSCs by lattice-matching of ZB/WZ-ZnSe bilayer to chalcopyrite sub-layer and ZnO over-layer. (c) 2018 The Electrochemical Society.