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Organic-inorganic halide perovskite solar cells have recently emerged as high-performance photovoltaic devices with low cost, promising for affordable large-scale energy production, with laboratory cells already exceeding 20% power conversion efficiency (PCE). To date, a relatively expensive organic hole-conducting molecule with low conductivity, namely spiro-OMeTAD (2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine) 9,9'- spirobifluorene), is employed widely to achieve highly efficient perovskite solar cells. Here, we report that by replacing spiro-OMeTAD with much cheaper and highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) we can achieve PCE of up to 14.5%, with PEDOT cast from a toluene based ink. However, the stabilized power output of the PEDOT-based devices is only 6.6%, in comparison to 9.4% for the spiro-OMeTAD-based cells. We deduce that accelerated recombination is the cause for this lower stabilized power output and postulate that reduced levels of p-doping are required to match the stabilized performance of Spiro-OMeTAD. The entirely of the materials employed in the perovskite solar cell are now available at commodity scale and extremely inexpensive.

We report a method of fabricating a high work function, solution processable vanadium oxide (V2O x(sol)) hole-extracting layer. The atmospheric processing conditions of film preparation have a critical influence on the electronic structure and stoichiometry of the V2O x(sol), with a direct impact on organic photovoltaic (OPV) cell performance. Combined Kelvin probe (KP) and ultraviolet photoemission spectroscopy (UPS) measurements reveal a high work function, n-type character for the thin films, analogous to previously reported thermally evaporated transition metal oxides. Additional states within the band gap of V2O x(sol) are observed in the UPS spectra and are demonstrated using X-ray photoelectron spectroscopy (XPS) to be due to the substoichiometric nature of V2O x(sol). The optimized V2O x(sol) layer performance is compared directly to bare indium–tin oxide (ITO), poly­(ethyleneoxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), and thermally evaporated molybdenum oxide (MoO x ) interfaces in both small molecule/fullerene and polymer/fullerene structures. OPV cells incorporating V2O x(sol) are reported to achieve favorable initial cell performance and cell stability attributes.

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