P-Type DSSCs by sensitizing a benzofuran[b]-fused BODIPY with cyanoacrylic acid

Abstract

We found that a benzofuran[b]-fused 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with cyanoacrylic acid (1) served as a photosensitizer for p-type dye-sensitized solar cells (DSSCs). The photovoltaic parameters (short circuit current density = 3.57 mA cm2, open circuit voltage = 0.12 V, fill factor = 0.33, and power conversion efficiency = 0.14%) were obtained with a 1-loaded NiO photocathode under AM 1.5 conditions. The incident photon-to-current efficiency spectrum showed excellent photo-harvesting capability, with a significant band at approximately 600 nm. Time-dependent density functional theory (TD-DFT)/DFT calculations indicated that electron distributions of both the HOMO and LUMO levels spread over the benzofuran-fused BODIPY core, mainly owing to π-π* transition. It is noteworthy that 1 served as a photosensitizer for p-type DSSC, despite almost no push-pull sensitizers. The hole transport and recombination processes were investigated by using intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. This study demonstrates that the local excitation (LE) character of dye is significantly workable for p-type sensitization, which may contribute to surpass recombination.