Preparation and characterization of MoO₃ hole-injection layer for organic solar cell fabrication and optimization

A facile, solution-processed method to fabricate MoO₃ (s-MoO₃) thin film as hole-injection layer (HIL) for poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM) based organic bulk hetero-junction photovoltaics is presented. The structural, electronic property and surface microstructure of the s-MoO₃ thin film are investigated in detail by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, scanning electron microscopy and atomic force microscope. The results indicate that the s-MoO₃ thin film possesses appropriate morphological, optical and electronic properties to be suitable for organic photovoltaic applications. The photovoltaic devices have been investigated and optimized in detail by tuning layer thickness, processing temperature and time, annealing conditions of interfacial layers. Using s-MoO₃ thin film as hole-injection layer, the device gives open circuit voltage of 0.64 V, circuit current density of 9.15 mA cm^-2, fill factor of 0.67 and power conversion efficiency of 3.92%, which is higher than the controlled device using PEDOT:PSS layer. In addition, the s-MoO₃ based devices exhibit good stability.