Enhanced Efficiency and Stability for the Inverted High-Bandgap Perovskite Solar Cell via Bottom Passivation Strategy

The bottom perovskite with the hole transport layer (HTL) in inverted perovskite solar cells (PSCs) interface has received little attention due to challenges like interlayer dissolution during perovskite deposition. And voids at the perovskite/HTL interface can degrade cell performance. This work introduces a two-dimensional (2D) perovskite layer between the perovskite and poly (N, N′-bis-4-butylphenyl-N, N′-bisphenyl) benzidine (Poly-TPD) HTL using a mixed solution of 4-methylphenethylammonium chloride (4M-PEA-Cl), methylammonium iodide (MA-I), and Poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide (PFN-Br). The amine functional groups in the organic salts improved HTL wettability, resulting in a void-free interface. 4M-PEA-Cl, with its strong electron-withdrawing benzene ring, outperformed other amine-containing salts in passivating undercoordinated Pb²⁺ ions. Incorporating this hybrid passivation layer in PSCs resulted in a 1.8% absolute increase in power conversion efficiency (PCE) to 19.1% with 1.68 eV perovskite bandgap. Additionally, the passivated PSCs demonstrated enhanced operational stability, retaining 91% of their initial efficiency after 800 hours of continuous 1-sun illumination, compared to 84.7% for the control sample.