Eco-friendly synthesis of regioregular poly(3-hexylthiophene) by direct arylation polymerization: Analysis of the properties that determine its performance in BHJ solar cells

A series of regioregular poly(3-hexylthiophenes) (rr-P3HTs) was synthetized by optimizing an eco-friendly Direct Arylation Polymerization (DArP) method, using as novel strategy, a gradual catalyst addition and temperature reaction increase improving P3HT quality. The polymers were analyzed and tested in organic solar cells (OSCs) in order to correlate the P3HTs properties with the power conversion efficiency (PCE). Results revealed that the best PCEs (3.6 and 3.4%) were reached with P3HTs of the highest RR (94 and 93% HT), with the lowest molecular weight (5.1 and 4.9 kDa) and, as X-ray diffraction in films and 2D-GIWAXS results endorse, with an edge-on orientation over the substrate, the largest size crystal and the highest Bragg's peaks, this latter feature could be the most effective reason to obtain the best PCEs. Theoretical calculations helped to understand how specific P3HT crystalline arrangements in the active layer favors the PCE.