Efficient organic photovoltaic cells with nano-domain control of the interpenetrating network morphology through post-thermal treatment

Regioregular poly(3-hexylthiophene) (rr-P3HT) is a promising candidate for polymer photovoltaic application for its stability and absorptions in the red region. We were able to obtain more efficient bulk heterojunction organic photovoltaic cells by using blend films of rr-P3HT and 1-(3-methoxycarbonyl)- propyl-l-phenyl-[6,6]-C61-butyric acid methyl ester (PCBM) subjected to a post thermal treatment process. Blend films of P3HT:PCBM = 1:0.8 weight-ratio were prepared using chloroform. Through a thermal annealing near the glass transition temperature (T_g), we examined the formation of nanodomains within the matrix. The improved nanoscale morphology, the increased crystallinity of the semiconducting polymer, and the improved contact to the electron collecting electrode facilitated charge generation and charge transport to and collection at the electrodes, leading to an enhanced device efficiency by lowering the series resistance of the organic photovoltaic cells.