In-Situ Solution Complexation for n-Type Surface-Energetics Reconstruction in 2.0 eV Ultra-Wide-Bandgap Perovskite Solar Cells

Abstract

Ultra-wide-bandgap (UWBG) perovskites (>2.0 eV) are essential for high-efficiency triple-junction tandem solar cells but suffer from photo-induced phase segregation and open-circuit voltage (VOC) deficits arising from surface defects and energetic misalignment. Here, we report an in situ solution complexation (ISC) strategy to reconstruct the surface of 2.0 eV perovskites. By exploiting a proton transfer reaction between phenethylammonium chloride and ethylenediamine, we activate the passivation agents to selectively deplete unstable surface iodine clusters and eliminate metallic lead defects. This chemical reconstruction induces a degenerate-like n-type surface with pronounced downward band bending, simultaneously forming a robust hole-blocking barrier and enabling efficient electron extraction via an Ohmic tunneling contact. Consequently, the ISC-treated 2.0 eV single-junction device achieves a power conversion efficiency (PCE) of 15.7% with a high VOC of 1.41 V and a fill factor of 0.84, while exhibiting superior photostability by suppressing phase segregation. Leveraging this UWBG top cell together with a 1.5 eV perovskite bottom cell, we further demonstrate a monolithic all-perovskite tandem solar cell delivering a PCE of 24.2% with a VOC of 2.58 V. This work provides a practical pathway to minimize voltage losses and stabilize UWBG perovskites, advancing perovskite tandems toward perovskite/perovskite/Si triple-junction architecture.