50% transparent solar cells of CuO /TiO2: Device aspects

Abstract

Abstract In this study, we have fabricated type-I straddling gap heterojunction solar cells of Ag/CuOx/TiO2/FTO configuration utilizing extremely thin p-n junction of 150 nm. We have studied four unique devices by varying the oxygen vacancies in CuOx and its effect on the overall performance of the cells. The average transmittance of 28–52% made these devices semitransparent for visual perception and transparent for visible spectrum of the Sun. The solar cell characteristics were recorded for 365 nm UV light which showed a linear increase in open circuit voltage (Voc) from 0.266 to 1.01 V while changing CuOx phases from Cu2O to CuO. However, a non-linear trend was observed for the photocurrent density and that has been discussed in detail by considering both material and device aspects. The optimized solar cell with CuO active layer possessed Voc of 1.01 V with 3.48 mA/cm2 current density and fill factor (FF) of 31% which sums up to an overall efficiency of 16.22% for an input power of 7 mW/cm2. The electrical parameters of solar cells were analyzed by using a two-diode model and the influence of TiO2 buffer layer has been discussed by the charge transfer mechanisms using the band diagrams. It was found that CuO/TiO2 device offered highest efficiency due to large Δ E c which increased the tunneling probability of minority charge carriers and reduced the recombination process at the interface. This study is the first experimental report on CuOx/TiO2 heterojunction solar cell which may find applications to design fancy and semitransparent power generating windows with colors yellow to brown by varying CuOx stoichiometry.