P-type P3HT interfacial layer induced performance improvement in chlorophyll-based solid-state solar cells

The insufficient charge extraction in chlorophyll-based solid-state solar cells (CSSCs) limits the photovoltaic performance, resulting in low photon-to-electron conversion efficiency. In this work, we employ poly(3-hexylthiophene) (P3HT) as a hole transporter to improve the charge extraction in CSSCs with a carboxylated chlorophyll sensitizer (H2Chl-1) adsorbed on mesoporous TiO2 as an electron acceptor and self-aggregates of a zinc chlorophyll derivative (ZnChl-2) as an electron donor. P3HT enhances the photon-to-electron conversion in both 300–540 nm and 660–725 nm wavelength regions. The charge recombination of CSSCs was suppressed by addition of P3HT to the ZnChl-2 aggregate layer that is spin-coated on H2Chl-1 adsorbed TiO2, as evidenced by the increased recombination resistance in the electrochemical impedance spectroscopy. As a result, the incident photon-to-electron conversion efficiency of the redmost peak of CSSCs with P3HT layer achieves a maximum value of 70.8%, and the power conversion efficiency is substantially enhanced from 2.1% to 3.1%.