A computational study of solvent effects on polymer photovoltaics considering the field dependendent series resistance

In order to fabricate high performance polymer solar cells, donor:acceptor mixture must be prepared using a proper solvent. Since solubility of C₆₀, as a truly cost effective acceptor, is very limited in common solvents, finding a suitable solvent can enhance the Poly(3-hexylthiophene):C₆₀ (P3HT:C₆₀) based solar cell performance in terms of short circuit current (J_SC), fill factor (FF) and consequently power conversion efficiency (PCE). The formation of C₆₀ aggregates and P3HT crystallinity depend on the selection of proper solvent. These two factors influence several electrical and optical properties of the cell. In this work, 1,2-Dichlorobenzene (ODCB), the most common solvent, and a mixture of 1-Chloronaphtalene and Chlorobenzene and 1-Methylnaphtalene and Chlorobenzene are chosen as two alternative solvents for preparing P3HT:C₆₀ films and simulation is performed to understand how these solvents influence the solar cell behavior. The performance of a P3HT:PCBM cell prepared with ODCB is also considered for comparison. A numerical model is employed to simulate the operation of different cells mentioned. In order to model the finite slope of I-V curve in large forward bias, the effect of voltage dependent series resistance is also considered. A minimizing algorithm is employed To determine the estimated values of unknown code input parameters, minimizing the fitting error of simulated and experimental I-V curves. Comparing the numerical model with conventional one shows that traditional models may not be accurate enough for analyzing organic photovoltaics. It is also shown that every 20% increase in G results in about 20% J_SC enhancement; this amount of increase is easily obtained using a proper solvent. Another crucial factor in determining solar cell performance is mobility which considerably depends on the solvent. This work provides experimentalists with an idea of how they should se- ect a solvent as a determinative material in solution-processed based solar cells. The results can also be generalized to find a proper solvent for other active layer materials.