Synergistic Effect of Ammonium Salts in Sequential Deposition toward Efficient Wide-Band-Gap Perovskite Photovoltaics with PCE Exceeding 20%

The controlled crystallization process is of significance to the morphological quality of wide-band-gap perovskite absorbers, especially with excessive bromide ions. Moreover, the non-radiative recombination assisted by surface defects is one of the major unfavorable factors that confines the development of highly efficient wide-band-gap perovskite solar cells (PSCs). Here, 1.65 eV wide-band-gap PSCs are constructed by a sequential deposition method with tailored morphology of highly reproducible perovskite absorbers. The controlled crystallization with the help of NH4Cl enables the perovskite films with larger and more uniform grains, which result in less bulk defects. At the same time, (NH4)2SO4 as a passivation layer reduces the uncoordinated Pb2+ and Pb0 defects on the surface of the perovskite film and improves the hydrophobicity due to newly formed insoluble PbSO4. Eventually, the synergistic effect of ammonium salts results in a high VOC of 1.18 V and an optimal efficiency of 20.43%, which is one of the highest power conversion efficiencies for 1.65 eV wide-band-gap-based PSCs constructed by a two-step deposition process. This work confirms that the sequential deposition method and addition of proper ammonium salts are effective strategies toward highly efficient and stable wide-band-gap PSCs.