Triple-cation perovskite solar cells with an inorganic two-dimensional tungsten diselenide hole transport layer for moisture stability

Metal halide perovskite solar cells (PSCs) have attained an impressive power conversion efficiency (PCE) of over 26% to date, in a period that is comparatively shorter compared to other solid-state semiconducting photovoltaic (PV) technologies. Some of the first reports on cell performance showed a PCE of ~ 3.8% in 2009, and issues of device stability remain topics of current exploration for many within the PV community. While the stability of the solar-cell stack is intimately tied to the fundamental qualities of the intrinsic perovskite absorber layer itself, the absorbers interaction with adjacent films within the solar cell stack are equally important as external factors influencing stability. In this work, we discuss the integration of the perovskite absorber with solution exfoliated inorganic tungsten diselenide (WSe₂) as an alternative to the conventional hole transport layer (HTL), Spiro-OMeTAD, where the latter is hydrophilic. The characterization of the solution exfoliated WSe₂ layer is first discussed with its heterostructures involving graphene ink-jet printed on flexible substrates, and subsequently, the integration of solution exfoliated WSe₂ as an alternative HTL to examine moisture stability of the PSC is then illustrated.