Enhanced performance of polymer solar cells with a fluorocyanophenyl compound as an additive

The efficiency of polymer solar cells (PSCs) with P3HT [poly(3-hexyl thiophene)]: PC₆₁BM [[6,6]-phenyl C₆₁-butyric acid methyl ester] blend film was improved by the incorporation of a fluorocyanophenyl compound, 3,4,5,6-tetrafluorophthalonitrile (TFP), as an additive. When the amount of TFT additive was 5 wt% based on the total amount of P3HT and PC₆₁BM, the highest efficiency was achieved. The annealed PSC with 5 wt% TFP had a power conversion efficiency of 4.45% compared with that (3.57%) of the reference cell without the additive, which corresponds to an increase of about 18.7% in the efficiency due to an enhancement in the short circuit current (J_sc). A seriese of measurements such as UV-visible absorption spectroscopy, X-ray measurements, atomic force microscopic images and incident photon to current conversion efficiency (IPCE) spectra revealed that the increased J_sc in the PSC with P3HT:PC₆₁BM:TFP blend film was due to an improvement in both exciton generation and charge transport efficiency, resulting from higher absorbance, larger crystal size and more effective phase separation.