Material layers at electrode/semiconductor interfaces are fundamental to the photovoltaic properties of polymer solar cells. The precise relationship between open-circuit voltage Voc and the work function (Φ) of the layers is still a matter for debate. Here we present a systematic study on over more than 20 cell architectures based on P3HT:PCBM with conductive polymers (PEDOT:PSS), metals (Ag, Au, Cr, Ca, Ti, Al), evaporated and solution processed inorganic compounds (LiF, Cs2CO3) and transparent metal oxides (ITO, FTO, MoO3, TiOx). We find a clear dependence of Voc with the work function of these electrodes characterized by a linear trend with slope (S) of 0.55, higher than values showed in literature, until the pinning regime is reached where saturation of the voltage is observed (S~0). Simulations enable to understand the physical origins of Voc, key to achieve high-performance devices. Through thin films of TiOx and Cr, we demonstrate the control of the polarity of the solar cell by tweaking the material inserted between top electrode (Cr/Au) and active layer. Comparison between more conventional (TiO2 and PEDOT:PSS, ΔΦ ≈ 0.8eV) and more recent materials (Cs2CO3 and MoO3, ΔΦ ≈ 2.1eV) allowed us to enhance the efficiency of the device from 3.6% to 4.4%, due to an increase in Voc, from 550mV to 620mV. Our study based on changing simultaneously electron and hole transport layers represents a promising method to optimize the design of high-efficiency polymeric solar cells.     «

Material layers at electrode/semiconductor interfaces are fundamental to the photovoltaic properties of polymer solar cells. The precise relationship between open-circuit voltage Voc and the work function (Φ) of the layers is still a matter for debate. Here we present a systematic study on over more than 20 cell architectures based on P3HT:PCBM with conductive polymers (PEDOT:PSS), metals (Ag, Au, Cr, Ca, Ti, Al), evaporated and solution processed inorganic compounds (LiF, Cs2CO3) and transparen...     »