Effect of Annealing Solvent Solubility on the Performance of Poly(3-hexylthiophene)/Methanofullerene Solar Cells

Abstract

The effect of the solubility of the annealing solvent on the performance of poly(3-hexylthiophene) (P3HT):C61-butyric acid methyl ester (PCBM) solar cells is studied. The short-circuit current (Jsc) and the fill factor (FF) increase remarkably, regardless of the type of annealing solvent, whereas a reduction of the open-circuit voltage (Voc) (of 0.1−0.2 V) is observed after solvent annealing. Interestingly, both the value of Jsc and the power conversion efficiency (PCE) are higher for the poor-solvent-annealed devices than for the good-solvent-annealed ones. A good solvent vapor induces better self-organization of P3HT than a poor solvent vapor. However, the exciton loss increases due to excessive phase separation. A study of the space-charge-limited current (SCLC) reveals no significant differences between the carrier mobilities of good- and poor-solvent-annealed devices. Furthermore, the measured photocurrent suggests that the space charges no longer limit the values of Jsc and FF for all the solvent-annealed devices. These results indicate that the higher Jsc and PCE values obtained for the poor-solvent-annealed devices can be attributed to the optimized phase separation of the active layers, which induces balanced carrier mobility and minimum exciton loss.