Efficient and thermally stable BHJ solar cells based on a soluble hydroxy-functionalized regioregular polydodecylthiophene

A new regioregular polythiophene derivative, called poly[3-(12-hydroxydodecyl)thiophene] (PT12OH), was synthesized by post-functionalizing its ω-brominated precursor poly[3-(12-bromododecyl)thiophene] (PT12Br) prepared using the Grignard metathesis route. Thanks to the optimal balance between hydrophilic and hydrophobic groups within its structure, PT12OH was highly soluble and easily filmable from common organic solvents allowing for its complete characterization. It also showed enhanced thermal properties, crystallinity, and self-assembling capabilities by the formation of strong inter- and intrachain hydrogen bonds. Bulk heterojunction photovoltaic cells with PT12OH and PC61BM showed a PCE of 4.83% and a remarkable over-time stability, offering good photoconversion efficiency even after 120 h of accelerated aging. Indeed, the PCE decrease was 34% for the hydroxylated polymer and 65% for its brominated precursor. It should also be pointed out that the enhanced thermal stability of PT12OH was achieved without resorting to any complex post-annealing photochemical, thermal, or chemical treatment and was thus directly ascribable to the polymer chemical structure. The simple and effective synthetic procedure, photovoltaic efficiency, and enhanced stability revealed the potential of PT12OH for large-scale organic solar cell applications.