Solution-processed small molecular photocells with neat fullerene

Because of ease in ensuring chemical integrity and purification, small molecular materials are promising as alternatives for polymeric electron-donor materials in solution-processed bulk heterojunction (BHJ) photocells. On the other hand, replacement of modified fullerene with neat one potentially reduces both economical and environmental costs of the photocells. In this paper, solution-processed BHJ photocells with a small molecular electron-donor 7,7′-[4,4-bis(2-ethylhexyl)-4H-silolo [3,2-b:4,5-b′]dithiophene-2,6-diyl]bis[6-fluoro-4-(5′-hexyl-[2,2′-bithiophen]-5-yl)benzo[c][1,2,5]thiadiazole] (p-DTS(FBTTh2)2) and neat C70 are studied. The devices showed a power conversion efficiency of approximately 1.3% after optimal thermal annealing. Analysis of current-voltage characteristics using an equivalent circuit model suggests that the thermal annealing enhances not only the generation but also the internal recombination of photocarriers.