Cadmium Selenide (CdSe) as an active absorber layer for solar cells with Voc approaching 750 mV

Cadmium Selenide (CdSe) is a semiconductor material with a band gap (1.74 eV) suitable for top cell for the fabrication of tandem devices. Here we explore the optoelectronic properties of evaporated CdSe and the subsequent device performance. The as-deposited CdSe film (thickness ∼800 nm) has small grains t ∼ 200–500 nm) that grow to the order of several microns after cadmium chloride (CdCl₂) treatment. In addition, the CdCl₂ treatment yielded enhanced photoluminescence (PL) response and long carrier lifetime. However, in addition to a significant band edge PL, we observe a wide peak at energies below the bandgap, suggesting defect states in the absorbance affecting the recombination in the device. The CdSe material was used as an active layer in photovoltaic devices (device structure SnO₂/CdSe/HTLs/Au) and achieved a device efficiency of 2.6% with Voc exceeding 750 mV, FF of 56%, and Jsc of 6.1 mAcm^-2 when illuminated through the thin Au (front) side. The device efficiency can be improved by replacing gold (Au, 10 nm) which has relatively poor transmittance and sheet resistance. We will discuss the comprehensive evaluation of CdSe films and devices for the photovoltaic application.