Influence of the electron buffer layer on the photovoltaic performance of planar Sb2(SxSe1‐x)3 solar cells

Appropriate selection of electron buffer layer and understanding its impact on the photo‐generated charge transfer dynamics at the interfaces are critical to enhance the efficiency of solar cells. By optimizing a multilayer electron buffer composed of CdS thin film deposited on TiO2 compact layer, we obtained a power conversion efficiency (PCE) of 5.47% for a planar solar cell of Sb2(SxSe1‐x)3 absorber. The PCE was significantly enhanced in the photovoltaic parameters of planar solar cells fabricated with single‐layer configuration: for example, PCE of 3.99% and 0.79% were obtained when either CdS or TiO2, respectively, were used. Surface photovoltage spectroscopy, transient photovoltage, and electrochemical impedance spectroscopy analyses indicated that the PCE improvement can be ascribed to a combination of 2 factors: (i) better separation and transfer of the photo‐excited free charge, provided by the beneficial energy level alignment between TiO2 and CdS layers, and (ii) sulfur passivation upon incorporation of CdS in a multilayer configuration causing a reduction in the trap states at the interface with Sb2(SxSe1‐x)3. By optimizing a multilayer electron buffer with a device configuration of FTO/c‐TiO2/c‐CdS/Sb2(SxSe1‐x)3/C/Ag, we have obtained a power conversion efficiency of 5.47% with a Voc of 0.51 V for a planar solar cell of Sb2(SxSe1‐x)3 absorber. Moreover, a substantial reduction of recombination rate contributing toward a decrease in the trap state density at the electron buffer/Sb2(SxSe1‐x)3 interface was confirmed by transient surface photovoltage and electrochemical impedance spectroscopy.