Perovskite Homojunction Solar Cells by Buried Interface Engineering

Abstract Constructing a strong p–n junction is an effective strategy to drive the separation of photogenerated charge carriers and boost the photovoltaic performance of solar cells. However, forming p‐type and n‐type semiconductors in perovskites is not as straightforward as in archetypal Si by doping electron‐accepting and electron‐donating elements. Here, we observe the transition of p‐type to n‐type characteristics in a perovskite layer via buried interface engineering. The perfluorinated copper phthalocyanine (F 16 CuPc) molecules with strong electronegativity are employed to modify the NiO x /Me‐2PACz substrate, which not only facilitates the crystallization of the perovskite, but also induces the formation of p‐type perovskite at its buried interface. We observe a gradual shift of the Fermi level from near valence band at the perovskite buried interface to near conduction band at the perovskite top surface, manifesting the transition from p‐type to n‐type within the monolithic perovskite layer. Such a p–n homojunction provides an extra electric field for accelerating charge carrier transportation, and thus enhances the device photovoltaic performance. The F 16 CuPc induced perovskite homojunction solar cells achieved a champion efficiency of 25.0% and it retained over 80% of its initial efficiency for more than 1100 h. We believe that the perovskite homojunction strategy will also pave the way for other perovskite‐based optoelectronic devices.