The effect of PbS nanocrystal additives on the charge transfer state recombination in a bulk heterojunction blend

Abstract

Abstract A persistent limitation of organic semiconductors is their low dielectric constant єr, which limits the performance of bulk heterojunction (BHJ) solar cells. One way to increase єr is to employ high-єr additives, such as PbS nanocrystals (QDs) to BHJ blends. In this work, we use the recombination of the interfacial charge transfer (CT) state as a means to study the effects of PbS nanocrystals on blends of a narrow bandgap copolymer: poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1- b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT), and phenyl-C61-butyric acid methyl ester (PCBM). We show that at low dilution levels (0.25% - 0.75% by weight), there is a decrease in the relative weight of the CT recombination lifetime (longer decay component); suggesting that there is an increase in the local єr of the ternary blend.