Control of the nanoscale crystallinity and phase separation in polymer solar cells

Grazing-incidence x-ray diffraction and atomic force microscopy were performed on bulk heterojunction regioregular poly(3-hexylthiophene) (RR-P3HT) [6,6]-phenyl-${\mathrm{C}}_{71}$ -butyric acid methyl esters spin-cast films with different film processing conditions to correlate the crystalline nanostructure of P3HT with the corresponding solar cell performance. The increase in long wavelength absorption for solvent annealed films is related to highly conjugated crystal structure of RR-P3HT phase-separated in the active layer. Upon thermal annealing, the solvent annealed $50\text{-}\mathrm{nm}$ -thick device shows high solar cell performance with fill factor up to 73% and power conversion efficiency of 3.80%.