V₂O₅-PEDOT: PSS bilayer as hole transport layer for highly efficient and stable perovskite solar cells

Hybrid halide perovskite solar cells (PSCs) have emerged as a strong candidate for low cost photovoltaics, owing to ease of processing and material abundance. The stability and performance of these devices are contingent on the quality of the interfaces. In this work, we report the novel interface engineered hole transport layer (HTL), incorporating Vanadium Pentoxide (V2O5) and Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) bilayer (PVO) for efficient charge transport in the devices. The devices incorporating the PVO bilayer HTL exhibits 20% higher power conversion efficiency (PCE) than conventional PEDOT only devices. The PSCs incorporating the PVO bilayer HTL demonstrated superior electronic properties as evaluated using impedance spectroscopy measurements. The recombination resistance (RRec) of the bilayer based devices are 57% higher than the reference cells. In addition to high charge selectivity, the bilayer PSCs exhibit low interfacial capacitance originating from electrode polarization and almost zero hysteresis. Furthermore, the bilayer based devices are more stable than PEDOT only devices; retaining 95% of their initial PCE even after 18 days of testing. The mechanism behind superior charge transport in PVO bilayer HTL and its role in stability enhancement are also discussed.