The Influence of Transport Layers on the Performance of Organic Solar Cells Studied by Drift-Diffusion Model

The existence of a hole transport layer (HTL) and an electron transport layer (ETL) in organic solar cells (OSCs) was considered in the drift-diffusion model (DDM) in a simplified way: domain for solving the DDM equations was divided into three subdomains corresponding to the HTL, an active layer (AL) and the ETL. Different material parameters such as electron and hole mobility, dielectric permittivity, recombination rate, and absorption coefficient, characterizing each layer, were applied for each subdomain. The Dirichlet boundary conditions were used on electrode/transport layer (TL) interfaces. The boundary conditions on TL/AL junctions were omitted so that TLs were accounted only through each layer material parameters. The DDM simulations were carried out by assuming photogeneration only in the AL. To examine the validity of our approach, dependencies of power conversion efficiency, fill factor, open circuit voltage and short circuit current density on the mobilities of majority and minority carriers in the HTL and ETL as well as on the recombination rates in these layers were determined and it was checked whether they meet the expected trends. Further, the current density–voltage (J-V) curves were simulated using the DDM which accounts for the TLs and the standard DDM not taking into account the TLs for ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al solar cell, and obtained results were compared to the experimental ones from literature. Simulated J-V curves matched well the experimental data when TLs were included.