Famished Two-Step Deposition for Self-Assembly Energy Cascade in the Perovskite Layer toward Efficient Photovoltaics

Nonradiative recombination arising from ionic vacancies and energetic barriers is one of the main limiting factors on the power conversion efficiency of state-of-the-art perovskite solar cells. Herein, a famished two-step sequential deposition method was developed to fabricate perovskite thin films, which can bring in synergistic effects combining defect passivation to reduce unintentional defects and favorable energy-level alignment for efficient charge transport. Under a famished growth condition when the molar ratio of the PbI2 and organics is more than 1, the organic-inorganic interactions in the perovskite unit can be significantly enhanced. Moreover, the perovskite boundaries and surface were terminated by the residual PbI2 which can efficiently eliminate the nonradiative recombination, enabling a high photoluminescence quantum efficiency. In addition, the as-fabricated perovskites exhibited a different electronic structure due to the different regional ratio of PbI2 and organic species during the perovskite growth, resulting in an energy cascade structure within the perovskite layers to facilitate charge transport and extraction. As a result, a champion efficiency more than 20% with enhanced stability was obtained via this simple famished sequential deposition route.