21.41%‐Efficiency CsPbI₃ Perovskite Solar Cells Enabled by an Effective Redox Strategy with 4‐Fluorobenzothiohydrazide in Precursor Solution

Abstract

To simultaneously stabilize cesium lead triiodide (CsPbI3) precursor solution and passivate the defects in CsPbI3 film is greatly significant for achieving highly stable and efficient CsPbI3 perovskite solar cells (PSCs). Herein, an effective redox 4‐fluorobenzothiohydrazide (FBTH) is developed to stabilize the precursor solution and passivate iodine/lead‐related defects for high‐quality CsPbI3 film. The comprehensive research confirms that 1) a new compound FBTH‐I is obtained from an effective redox interaction between FBTH and molecular iodine (I2) in perovskite precursor solution, which can effectively impede the formation of I2 molecule and restrain I− migration in perovskite film by forming N–H···I bond; 2) FBTH‐I can also passivate Pb‐related defects via forming S···Pb interaction. Consequently, the CsPbI3 PSC based on FBTH‐treated precursor solution exhibits a fascinating power conversion efficiency (PCE) of 21.41%, which is one of the highest PCE values among the reported pure CsPbI3 PSCs so far, and an outstanding stability against the harsh conditions, such as thermal annealing and continuous light‐illumination.

A comparison of molecular iodine evolution on the chemistry of lead and tin perovskites

“…174 Recently, 4-fluorobenzothiohydrazine was shown to stabilise all-inorganic CsPbI 3 enabling a PCE of 21.41%, amongst the highest reported values for fully inorganic PSCs. 175 Likewise, Zhang et al used hydrazine sulfonate to stabilise narrow band-gap (≈1.24 eV) Pb–Sn binary PSCs enabling high PCEs of 23.17%. 176 To this end, several hydrazine derivatives have been incorporated within PSCs owing to high oxidation potentials (Fig.…”