Solution-processed tungsten diselenide as an inorganic hole transport material for moisture-stable perovskite solar cells in the n-i-p architecture

Abstract

Some of the obstacles to the commercialization of perovskite solar cells (PSCs) are their long-term moisture stability and material cost of the constituent layers, such as the commonly used spiro-OMeTAD hole transport layer (HTL). Replacing the spiro-OMeTAD with low-cost inorganic hole transport materials (HTMs) are important to further elevate the attractiveness of PSCs for commercialization. Perovskite-compatible, solution-exfoliated two-dimensional (2D) transition metal dichalcogenides (TMDCs) are being considered as viable candidates for inorganic HTMs. We consider one such TMDC, WSe₂ which was chemically exfoliated using dichlorobenzene (DCB), a perovskite-compatible solvent, as it was integrated with triple cation perovskite absorbers within the solar cell stack. The WSe₂ HTL required heat treatment processes to be maintained below 100 °C in order to preserve the integrity of the underlying perovskite; despite this lower temperature post treatment process, the structural morphology of the film revealed its dense and pinhole-free nature. Temperature-dependent transport studies conducted on the WSe₂ film provided evidence of its semiconducting character and its ability to extract holes well from the underlying triple-cation Cs_0.05FA_0.79MA_0.16PbI_2.45Br_0.55 absorber. The inorganic HTL offered better environmental stability in moisture-rich environments of up to 60 % relative humidity, in comparison to spiro-OMeTAD HTL-based devices which degraded faster as a result of pinholes.