Highly Efficient Selenium Thin Film Indoor Photovoltaic Device Using Te Precision Deposition Technique

This paper proposes a precise deposition of Te adhesion layer for improving device performance of Se thin film based photovoltaic devices. The aim is to enhance the adhesion between the TiO2 (or ZnMgO) and Se layers while limiting the detrimental effects of excessive Te layer which causes unfavorable leakage at pn junction, resulting in an obvious improvement of the power conversion efficiency of Se heterojunction photovoltaic devices. A reproducible deposition technique at slower deposition rate (∼0.5 Å/s) is proposed by controlling the crucible temperature during tellurium deposition. TiO2/Se photovoltaic device improved the photovoltaic conversion efficiency from 2.37% to 3.52% under light illumination at AM1.5, 100 mW/cm2 (1 sun calibrated with a solar simulator) by decreasing Te film thickness from 5 nm to 1 nm. It is considered that the increased open circuit voltage from 0.529 V to 0.687 V, attributed to the decreased dark leakage current at pn junction by decreasing Te layer thickness 5 nm to 1 nm. Almost three folds of power conversion efficiency was obtained under indoor LED illumination as compared to that under 1 sun light illumination because of the optimum bandgap energy of Se to indoor light spectrum.