Construction of efficient perovskite solar cell through small-molecule synergistically assisted surface defect passivation and fluorescence resonance energy transfer

Perovskite films are apt to format defects on surface and in grain boundaries, which results in inferior photovoltaic performance. Moreover, perovskite materials are sensitive to Ultraviolet (UV) light and are easily damaged under UV light illumination, accelerating the degradation of Perovskite solar cells (PSCs). Therefore, it is significant to design and develop effective defect passivation and UV inhibitors for efficient and stable PSCs. Herein, a small molecular material 2,5-bis(perfluorophenyl)thiazolo[5,4-d]thiazole (PFP2TTz) was designed and introduced into the perovskite precursor solution. The research manifested that PFP2TTz is a bifunctional additive, acting as both defect passivation and Fluorescence resonance energy transfer (FRET) agents. Through FRET action, the spectrum response in the short wavelength region and the device stability under UV light illumination were remarkably enhanced. Moreover, the PFP2TTz-treatment can significantly decrease the trap state density of perovskite film. Correspondingly, the PFP2TTz-treated PSC device exhibited an impressive Power conversion efficiency (PCE) of 21.38%, which is much higher than the control device (19.27%). Meanwhile, the unencapsulated PFP2TTz-treated PSC device exhibits long-term stability, maintaining their initial PCE of 90.4% up to 30 days under relative humidity of 45–55%.