Optical and electrical features of calcium molybdate scheelite solar cells

Abstract

Calcium molybdate (CMO) is a material used in several technological applications. In this work, we explored the correlation between the optical and electrical properties of CMO in solar cell photoanodes. Six samples were prepared by a microwave-assisted hydrothermal method with pH values of 4, 7, and 10 associated with temperatures of 100 °C and 140 °C. These samples were used as a replacement for titanium dioxide TiO₂ in Graetzel solar cells. A thin blocking layer (BL), a dense and translucent film, was deposited over a CMO layer using a doctor-blade method, to create a heterojunction. We show that a strict correlation between pH, temperature, processing time, and photovoltaic response exists in CMO scheelite and needs to be considered to achieve optimal photovoltaic behavior. Almost all samples achieved typical solar cell responses, except that synthesized with pH 4 at 100 °C, which shows an anomalous behavior. Among these samples, the one synthesized with pH 10 at 100 °C was identified as the most suitable candidate for down-converter materials in solar energy applications, due to its typical diode-like properties, with an upper J_sc = 180 μA cm⁻², V_oc = 607 mV and FF = 0.45.