Increased photon absorption and conversion in ternary bulk heterojunction systems of CdSe/CdS core-shell nanoparticles/methyl viologen composites, conjugated polymers, and fullerenes

Increasing the conversion of photon flux into electrical energy is the driving problem in organic photovoltaic research. We address this problem by incorporating CdSe/CdS ´core-shell´ nanoparticles conjugated with methyl viologen (a strong electron acceptor) into two separate bulk heterojunction systems. The first is based on poly(3-hexylthiophene) (P3HT), and[6,6]-phenyl-C61-butyric acid methyl ester (PC₆₁BM), while the second is based on poly[(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b; 3,4-b´]-dithiophene-2,6-diyl)-alt- (2,1,3-benzothiadiazole-4,7-diyl)] (PCPDTBT) and PC₆₁BM. We show that in both cases the addition of these nanoparticle composites can lead to an increase in photocurrent. However the nature of the photocurrent increase could be through direct absorption and/or indirect mechanisms depending on the system.