Universal Efficiency Improvement in Organic Solar Cells Based on a Poly(3-hexylthiophene) Donor and an Indene-C60Bisadduct Acceptor with Additional Donor Nanowires

With poly(3-hexylthiophene) (P3HT) nanowire (NW) inclusion in active layers (ALs), organic solar cells (OSCs) based on P3HT donor and indene-C60 bisadduct (ICBA) acceptor showed power conversion efficiency (PCE) improvements for both bulk heterojunction (BHJ)- and bilayer (BL)-structure AL devices. The PCE increase was approximately 14 % for both types of P3HT:ICBA OSCs. However, improvements in short-circuit current density (Jsc ) were about 4.4 and 6.4 % for BHJ- and BL-type AL devices, respectively. A systematic study showed that the addition of P3HT NWs did not result in enhanced internal quantum efficiencies for either type of device. However, the difference in light-harvesting efficiency was important in accounting for Jsc variations. Interestingly, there was no correlation between Jsc and PCE variations, whereas the open-circuit voltage (Voc ) and fill factor (FF) showed correlations with the PCE. The variation in FF is discussed in terms of Voc and equivalent-circuit parameters based on a nonideal diode model.