Comprehensive simulation of binary and ternary bulk-heterojunction solar cells: a kinetic Monte Carlo and multimethod approach

Ternary bulk heterojunction (BHJ) organic solar cells improve efficiency by incorporating a third component to optimize charge generation and transport. In this study, we developed a Kinetic Monte Carlo (KMC) model to investigate their properties. Generation rates were calculated using the Transfer Matrix Method, which accounts for probability distribution across film depth and material phases. Binary and ternary BHJ structures were simulated using an Ising model with a Kawasaki spin exchange algorithm. The donor polymer D18 serves as the primary donor, while PTB7-Th is introduced as a secondary donor to enhance light absorption and exciton separation. The non-fullerene acceptor L8-BO functions as the electron acceptor. To better align the open-circuit voltage (V_oc) and fill factor (FF) with experimental results and Drift-Diffusion (D-D) models, PEDOT:PSS and PNDIT:F3N were integrated as hole and electron transport layers. Instead of using the cathode-anode work function difference, the maximum internal electric field was calculated based on the average charge collection levels involved the transport layers and the corresponding electrodes, which leads to improvement in FF, although V_oc was notably overestimated. Analysis of J-V characteristics revealed that short-circuit current density increased almost linearly with the generation rate, correlating with higher PTB7-Th composition, while FF decreased due to PTB7-Th’s lower hole mobility. Future work will refine input parameters, improve interfacial property more realistically by incorporating trap states, and address the impact of film disorder on device performance.