Photo-Carrier Recombination in Polymer Solar Cells Based on P3HT and Silole-Based Copolymer

Photo-current loss in donor-acceptor (DA) polymer-fullerene bulk heterojunction solar cells was studied via carrier transport and recombination measurements. Focusing on the DA polymer poly((4,4-dioctyldithieno (3,2-b:2',3'-d) silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (DTS-BTD) we found that the carrier transport is well-balanced and attribute the loss mechanism in DTS-BTD solar cells to carrier recombination. Using carrier extraction with linear increasing voltage (photo-CELIV) and transient photo-voltage (TPV), we show that carrier recombination plays an important role in photo-current extraction at open circuit conditions due to increase in photo-excited carrier concentration. Delay time dependent photo-CELIV and temperature dependent transport studies suggest that the recombination rate is related to the degree of energetic disorder in the polymer: fullerene blends.