Evaluation of Enhanced Stability and Performance of Perovskite Solar Cells using Inorganic Hole Transporting Materials

Abstract

Organic-inorganic lead halide perovskites have shown promise as cost-effective high-performance material for solar cells. Hole transport materials (HTMs) are currently the bottleneck for the realization of efficient cost-effective and stable devices. In this work, synthesis of novel hole-transporting materials based on spinel metal oxides (Co3O4, NiOx, Cu:NiOx, and NiCo2O4) with enhanced carrier mobility and conductivity using chemical precipitation method with high yields are presented. The focus of this research work is to investigate the effectiveness of spinel oxides as the hole transporting interlayer for perovskite solar cells (PSCs). The synthesized nanomaterials were characterized by various techniques including XRD, XAS, SEM and TEM to confirm the structure. Furthermore, the band-gap of the synthesized material was confirmed by UV-Vis spectroscopy and their valence band maximum (VBM) was determined by photo-electron spectroscopy in air (PESA). Valence band position of spinel oxides (Co3O4 = -5.3 eV, NiOx = -5.5 eV, and Cu:NiOx = -5.4 eV, NiCo2O4 = 5.5 eV) is quite close to valence band of perovskite (~ -5.4 eV). Thus, spinel oxides have a VBM compatible with perovskite, which can facilitate the efficient hole charge transfer. A thin layer of p-type in-organic spinel Co3O4, NiOx, Cu:NiOx and NiCo2O4 in PSCs provides a higher carrier mobility, better-energy level matching, and superior stability. Compared to standard PSC an improved efficiency of 11.65% with Co3O4, 12.79 % with Cu:NiOx, and 14.29 % with NiCo2O4 is achieved. Also, perovskite solar modules with spinel oxides layer is stable for more than 4500 hours in an ambient environment with PCE degradation of less than 5% of initial value. Electrochemical Impedance Spectroscopy (EIS) results reinforced the above outcomes by showing the decrease in recombination resistance (Rrec) of PSCs with spinel oxides interlayer. Finally, the fabrication of monolithic perovskite module is demonstrated, having an active area of 70 cm2 and showing a power conversion efficiency >11% with Co3O4 and 12.10 % with Cu:NiOx with virtually no hysteresis. This PCE is the highest ever reported efficiency as per our knowledge for such large area perovskite solar devices