Highly Efficient Wide Bandgap Perovskite Solar Cells With Tunneling Junction by Self‐Assembled 2D Dielectric Layer

Abstract Reducing non‐radiative recombination and addressing band alignment mismatches at interfaces remain major challenges in achieving high‐performance wide‐bandgap perovskite solar cells. This study proposes the self‐organization of a thin two‐dimensional (2D) perovskite BA 2 PbBr 4 layer beneath a wide‐bandgap three‐dimensional (3D) perovskite Cs 0.17 FA 0.83 Pb(I 0.6 Br 0.4 ) 3 , forming a 2D/3D bilayer structure on a tin oxide (SnO 2 ) layer. This process is driven by interactions between the oxygen vacancies on the SnO 2 surface and hydrogen atoms of the n‐butylammonium cation, aiding the self‐assembly of the BA 2 PbBr 4 2D layer. The 2D perovskite acts as a tunneling layer between SnO 2 and the 3D perovskite, neutralizing the energy level mismatch and reducing non‐radiative recombination. This results in high power conversion efficiencies of 21.54% and 19.16% for wide‐bandgap perovskite solar cells with bandgaps of 1.7 and 1.8 eV, with open‐circuit voltages over 1.3 V under 1‐Sun illumination. Furthermore, an impressive efficiency of over 43% is achieved under indoor conditions, specifically under 200 lux white light‐emitting diode light, yielding an output voltage exceeding 1 V. The device also demonstrates enhanced stability, lasting up to 1,200 hours.