3D/2D Core/Shell Perovskite Nanocrystals for High‐Performance Solar Cells

All‐inorganic lead halide perovskite nanocrystals (NCs) emerge as a rising star in photovoltaic fields on account of their excellent optoelectronic properties. However, it still remains challenging to further promote photovoltaic efficiency due to the susceptible surface and inevitable vacancies. Here, this work reports a 3D/2D core/shell perovskite heterojunction based on CsPbI3 NCs and its performance in solar cells. The guanidinium (GA+) rich 2D nanoshells can significantly passivate surface trap states and lower the capping ligand density, resulting in improved photoelectric properties and carrier transport and diminished nonradiative recombination centers via the hydrogen bonds from amino groups in GA+ ions. Consequently, an outstanding power conversion efficiency (PCE) of up to 15.53% is realized, substantially higher than the control device (13.77%). This work highlights the importance of surface chemistry and offers a feasible avenue to achieve high‐performance perovskite NCs‐based optoelectronic devices. Ultrathin 2D perovskite shell is fabricated to passivate the CsPbI3 nanocrystals, in which organic cation guanidinium is introduced onto the host surface. The 2D perovskite nanoshell on CsPbI3 nanocrystals can effectively repair the defects without weakening the charge transport between adjacent nanocrystals. Solar cells based on the core/shell nanocrystals can achieve a champion power conversion efficiency (PCE) of up to 15.53%.