Effects of passivated molecular side group on inverted inorganic CsPbI2Br perovskite solar cells

The advancement of efficient and stable inverted CsPbI2Br perovskite solar cells (PSCs) is imperative for their unique advantages of eliminating detrimental dopants and enabling compatible processes with tandem cells in comparison with the regular structures. However, the progress of this structure lags due to its relatively low open circuit voltage (Voc). Herein, we present an effective surface passivation strategy using phenethylammonium iodides with a different side group to ameliorate the aforementioned issues. It has been observed that 4-methyl phenethylammonium iodide (MePEAI) with the –CH3 side group can effectively reduce the trap density of the perovskite film by forming interactions with the under-coordinated Pb2+ ions, thereby suppressing the nonradiative recombination. Additionally, this approach optimizes the energy-level alignment at the perovskite/PCBM interface. As a result, the optimized device demonstrates a substantially enhanced efficiency from 11.23 to 14.10 %. Furthermore, the MePEAI-treated device exhibits excellent long-term stability. The unencapsulated device retains 81.2 % of its initial power conversion efficiency (PCE) after being stored for over 2900 h in an N2 atmosphere.