Universal Efficiency Improvement in Organic Solar Cells Based on a Poly(3-hexylthiophene) Donor and an Indene-C60 Bisadduct 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-C-60 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 (J(sc)) 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 J(sc) variations. Interestingly, there was no correlation between J(sc) and PCE variations, whereas the open-circuit voltage (V-oc) and fill factor (FF) showed correlations with the PCE. The variation in FF is discussed in terms of V-oc and equivalent-circuit parameters based on a nonideal diode model.