Effect of polaron-pair recombination on magnetoconductance in organic solar cells

Abstract

The mechanism of magnetoconductance (MC) in organic solar cell based on poly(3-hexylthiophene) (P3HT) and $[6,6]-phenyl-C_{71}-butyric acid methyl ester (PC_{71}BM)$ remains unclear. Recombination of polaron pairs in the P3HT:PC71BM organic solar cell is important in view of MC and charge transportation. To examine whether the polaron-pair model is appropriate to explain the mechanism of MC in the $P3HT:PC_{71}BM$ system, we used an equivalent circuit model in which the internal shunt resistance represents the polaron-pair recombination. The almost identical dependence of MC and the magnetic field effect on the internal shunt resistance for the $P3HT:PC_{71}BM$ solar cells with various polaron-pair recombination rate clearly shows that the MC is ascribed to the polaron-pair recombination. The fact that the MC is virtually unaffected by light intensity under $100 mW/cm^2$ confirms that the polaron pairs that are responsible for the MC are of geminate nature. From the different MC behaviors of devices with 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2a-Aza-1,2(2a)-homo-1,9-seco[5,6]fullerene-C60-Ih-1,9-dione, 2a-[(4-hexyloxy)-3-methoxyphenyl]methyl] (KLOC-6), TCNQ is recognized that affects geminate polaron pair recombination in donor domain, while KLOC-6 affects nongeminate recombination in acceptor domain.