Optimizing device efficiency of P3HT/P3HT:PCBM interlayer organic solar cell: Annealing dependent study

The developments in the organic photovoltaics technology are mainly focused on increasing the power conversion efficiency (PCE), cost effective manufacturing and longer lifetime of the device. In this paper, effect of inserting the additional polymer layer between the hole transporting layer (HTL) and blended polymer: fullerene photoactive layer in conventional organic solar cell (OSC) has been demonstrated. The poly 3-hexylthiophene (P3HT) buffer layer inserted between HTL and P3HT:PCBM offers pure donor phase at the HTL interface which ultimately reduces the effect of vertical phase separation in conventional OSC. The experimental results shows that proposed buffered layer architecture has shown the improved power conversion efficiency (PCE) of OSC by $\sim$35% over the conventional OSC structure. This improvement are mainly due to increase in photon absorption and improved charge collection at the HTL interface. In addition to this, the annealing dependent study on proposed buffered layer OSCs and conventional OSCs has been carried out. It has been found that annealing the active layer for longer duration has substantially reduced the PCE of the both the OSC architecture. The reason for this drop in PCE is mainly because of increase in donor-acceptor phase segregation and vertical phase separation in P3HT:PCBM. Although, in comparison to the conventional OSCs the PCE of proposed buffered layer OSCs has not plunges drastically which indicates the reduced impact of vertical phase separation in case of novel buffer layer architecture.