Performance improvement of annealing-free P3HT: PCBM-based polymer solar cells via 3-methylthiophene additive

In this work, we studied the effect of 3-methylthiophene (3MT) and 3-hexylthiophene (3HT) additives on the morphology and photovoltaic performance of the polymer solar cells (PSCs) based on P3HT : PCBM (1 : 1 w/w). The P3HT : PCBM blend films prepared from the solutions with 3MT or 3HT additive show enhanced absorption in the 500-650 nm wavelength range and higher hole mobility than that of the film without the additives. X-ray diffraction data indicate a smaller interlayer distance of the conjugated backbones in the w3MT- or 3HT-processed films. Atomic force microscopy images of the 3MT-processed films demonstrate a nanoscaled phase separation and interpenetrating network morphology between the donor and the accept phases. The power conversion efficiency of PSCs based on 3MT-processed blend films without thermal annealing reached 3.72% which is increased by 30% over that of the devices without the additive.