Opto-Electrical Modelling and Performance Analysis of DPPEZnP-TBO-Based Organic Tandem Solar Cells: Impact of Charge Carrier Mobility

Organic tandem solar cells are gaining attention for their potential to combine high power conversion efficiency (PCE) with low-cost manufacturing. This study examines the optoelectrical performance of tandem solar cells based on DPPEZnP-TBO, with a focus on the critical role of charge carrier mobility. SETFOS (Fluxim) simulations were used to evaluate the electrical performance of the organic solar cell devices. Using transfer matrix methods, Optical modelling can perform an accurate analysis of light absorption and photogenerated current in multilayer structures. The electrical behaviour was assessed using a drift-diffusion model that incorporates carrier mobility, recombination, and interfacial effects to understand current-voltage (I-V) characteristics. This study demonstrates that hole mobility has a significant influence on the photovoltaic performance of the simulated tandem organic solar cell by affecting charge transport, recombination, and the resulting device parameters (J SC , V OC , FF, and PCE). A decrease in hole mobility reduced the PCE from 1.378% to 0.978%, primarily because slower hole transport increased charge accumulation and bimolecular recombination, thereby limiting charge extraction. Conversely, increasing hole mobility enhanced hole transport and increased the short-circuit current density (J SC ). However, excessive hole mobility created an imbalance between electron and hole transport, resulting in a decrease in the open-circuit voltage (V OC ). Thus, the photovoltaic performance reflects a trade-off between improved charge extraction at higher hole mobility and the adverse effects of charge transport imbalance, indicating the existence of an optimum hole mobility for maximising device efficiency. Additionally, optimising the thickness of active layers improved light absorption and current matching between sub-cells, boosting overall efficiency. The study highlights the importance of mobility control and structural optimisation in designing efficient organic tandem solar cells.