Fabrication of Improved p-AgGaSe2/n-Si Heterojunction Solar Cells on Optimum Quality Thermally Evaporated AgGaSe2 Thin Films

Abstract

ABSTRACTOptimum quality polycrystalline AgGaSe2 thin films were deposited on H-terminated n-Si substrates by controlled thermal evaporation method. The film deposition conditions were varied to optimize the structure and optoelectronic properties of AgGaSe2 thin films. X-ray diffraction (XRD) studies showed that all AgGaSe2 films were of chalcopyrite structure and while the films deposited at room temperature (300 K) had random grain orientation, the films deposited at higher substrate temperature (≥ 450K) showed preferred (112) orientation. The composition of the films were analyzed by electron probe microanalysis (EPMA) deposited at different substrate temperatures. The ultraviolet-visible (UV-Vis) spectra showed the optical bandgap of 1.80 eV, with sharper band edge for the films deposited at higher temperature. The films were p-type and the resistivities of the as deposited films at 300 and 650K were ~5×103 and ~200 Ω.cm respectively. p-AgGaSe2/n-Si heterojunction solar cells, having an active area of 0.18 cm2 without any antireflection coating were designed and fabricated. It was observed that the films deposited at 650K produced heterojunctions with significantly improved photovoltaic properties. The evidence of the barrier height modifications have been provided by C-V measurements. Under solar simulator AM1 illumination, the improved junction exhibited an efficiency of 5.2%, whereas the AgGaSe2 films deposited at 300K showed a lower efficiency of 2.1%.