Fullerene‐Free p–i–n Perovskite Solar Cells: Direct Deposition of Tin Oxide on Perovskite Layer Using Ligand Bridges

Abstract In p–i–n perovskite solar cells (PSCs), fullerene derivatives are predominantly used as an electron transport material (ETM) despite their disadvantages, such as parasitic absorption in the short wavelength range and high cost. State‐of‐the‐art n‐i‐p PSCs are fabricated using SnO 2 as the ETM due to their high charge transfer ability, transparency, and low cost. However, in p–i–n PSCs, dispersing SnO 2 nanoparticles in a solvent that does not damage the perovskite and forming a uniform layer is challenging. Herein, a strategy of directly depositing SnO 2 quantum dots (QDs) on perovskite using ethylenediamine (EDA) for high‐performance applications is reported, which involves a SnO 2 QD solution designed with a damage‐free cosolvent. Treating the SnO 2 QD layer with the EDA strategy creates a conformal SnO 2 QD layer and improves charge transport. This strategy achieves a high power conversion efficiency (PCE) of 18.9% in PSCs with a 1.77 eV bandgap, which is the highest PCE reported for wide bandgap p–i–n PSCs using an inorganic ETM. The top SnO 2 layer enables ITO deposition without sputtering damage and achieves a bifacial factor of 99% due to the high transmittance of SnO 2 QD. The resulting four‐terminal all‐perovskite tandem exhibited a PCE of 27.0%.