Constructing of superhydrophobic and intact crystal terminal: Interface sealing strategy for stable perovskite solar cells with efficiency over 23%

The numerous nonstoichiometric imperfections on the perovskite crystal terminal are usually resulting in unwished nonradiative recombination as well as high risk of lead leakage. Herein, the terminal sealing strategy by using pseudo-halide ammonium salts was developed to seal lattice defects via ion-exchange reaction and interact with uncoordinated Pb2+ at the terminal of the perovskite films. The superhydrophobic ammonium cations can bond to undercoordinated Pb2+ and I-/Br- on crystal terminal, impeding erosion from the environment. Furthermore, the terminal sealing layer modulated the energy level alignment between perovskite and holes transport layer to promote efficient extraction of the hole. The optimal device attained a power conversion efficiency (PCE) over 23% without obvious hysteresis. The unencapsulated devices maintained 90% of the original PCE after operation at 60 +/- 10% RH for 1200 h and exhibited a 20% loss in PCE after 500 h light soaking aging. More importantly, immersion operation further showed their superior structure stability against water. This work provides a unique perspective towards reconstructing the imperfect lattice defects and reducing lead leakage venture of perovskite crystal terminals.

Automated summary

The use of pseudo-halide ammonium salts to seal nonstoichiometric imperfections on the perovskite crystal terminal, and the interaction with uncoordinated Pb2+, has proven effective in reducing lead leakage and promoting efficient hole extraction.