Theoretical studies on the influence of graphene layers as an anode on the performance of P3HT:PC61BM and PTB7:PC71BM bulk heterojunction organic solar cells

In the present work, photovoltaic properties of P3HT:PC61BM bulk heterojunction solar cells based on graphene anode are investigated using the transfer matrix model and drift-diffusion model for optical and electrical performances, respectively. First, we study the effect of the number of graphene layers on optical and electrical performance. Light absorption and total exciton generation rate in active layer as well as photovoltaic parameters including the short circuit current density, open circuit voltage, fill factor, and power conversion efficiency are determined. The optoelectronic model suggests that short circuit current density decreases upon increasing the number of graphene layers, which is attributed to the reduction of light absorption in the active layer. Power conversion efficiency is found to be between 3.49 and 4.31 % for various numbers of graphene layers. Based on the calculation results, five-layer graphene anode is found to have the same sheet resistance as 150 nm-thick ITO anode. Second, the performance of five-layer graphene-based organic solar cell is compared with that of ITO-based anode device. The results indicate that the former can reach 84 % power conversion efficiency of the latter. Finally, P3HT:PC61BM replaces with PTB7:PC71BM as the active layer and its influence on device performance is studied.