Perovskite Homojunction Solar Cells by Buried Interface Engineering

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 metal halide perovskites is not as straightforward as in the archetypal Si by doping electron-accepting and electron-donating elements. Here we observe the transition of p-type to n-type characteristics in a monolithic perovskite layer via buried interface engineering. The perfluorinated copper phthalocyanine (F16CuPc) molecules with strong electronegativity are employed to modify the NiOx/Me-2PACz substrate, which not only facilitates the crystallization of perovskite, but also induces the formation of p-type perovskite at its buried interface. We observe a gradual shift of the Fermi level across bandgap from near valence band at perovskite buried interface to near conduction band at perovskite top surface, manifesting the transition of p-type to n-type within the monolithic perovskite layer. Such p-n homojunction in a perovskite solar cell provides an extra electric field for accelerating charge carrier transportation and thus enhances the corresponding device photovoltaic performance. The F16CuPc 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 hours.