Polymer bulk heterojunction solar cells employing Förster resonance energy transfer

There are two crucial tasks for realizing high-efficiency polymer solar cells (PSCs): increasing the range of the spectral absorption of light and efficiently harvesting photogenerated excitons. Here, we describe Forster resonance energy transfer-based heterojunction polymer solar cells that incorporate squaraine dye. The high absorbance of squaraine in the near-infrared region broadens the spectral absorption of the solar cells and assists in developing an ordered nanomorphology for enhanced charge transport. Femtosecond spectroscopic studies reveal highly efficient (up to 96%) excitation energy transfer from poly(3-hexylthiophene) to squaraine occurring on a picosecond timescale. We demonstrate a 38% increase in power conversion efficiency to reach 4.5%, and suggest that this system has improved exciton migration over long distances. This architecture transcends traditional multiblend systems, allowing multiple donor materials with separate spectral responses to work synergistically, thereby enabling an improvement in light absorption and conversion. This opens up a new avenue for the development of high-efficiency polymer solar cells.