| Abstract
| - In this report, we have studied the influence of the nature of the end groups (bromine or hydrogen) ofregioregular poly(3-hexylthiophene) (P3HT) polymers on the performance of polymer solar cells made withblend films of P3HT and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM). Films and devices werestudied before and after annealing at 140 °C for 2 h. The effects of the end-group type on the properties ofpristine polymers and blend films were examined using optical absorption and emission spectroscopy, transientabsorption spectroscopy, and measurements of photovoltaic device performance. It was observed that hydrogenend groups result in slightly higher absorption coefficients, higher photoluminescence intensities, faster andless dispersive charge recombination, and superior solar cell performance (notably a higher fill factor) comparedto bromine end groups. The results are attributed to more-ordered polymer-chain packing in blend filmsmade with hydrogen-capped P3HT, on account of the smaller size and weaker electrostatic interactions resultingfrom hydrogen compared to bromine. Some influence of the C−Br group on exciton quenching may also bepresent. The effect of the bromine end group on solar-cell performance became more pronounced with reducingincident-light intensity. Comparison of the polymer transport characteristics in organic field-effect transistorconfiguration indicated that the bromine end group enhances hole trapping.
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