We report the fabrication of high power conversion efficiency (PCE) polymer/fullerene bulk
heterojunction (BHJ) photovoltaic cells using solution-processed Copper (I) Iodide (CuI) as hole transport
layer (HTL). Our devices exhibit a PCE value of 5.5% which is equivalent to that obtained for
control devices based on the commonly used conductive polymer poly(3,4-ethylenedioxythiophene):
polystyrenesulfonate as HTL. Inverted cells with PCE>3% were also demonstrated using solutionprocessed
metal oxide electron transport layers, with a CuI HTL evaporated on top of the BHJ. The
high optical transparency and suitable energetics of CuI make it attractive for application in a range of
inexpensive large-area optoelectronic devices.