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 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 (F₁₆CuPc) 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 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 h. We believe that the perovskite homojunction strategy will also pave the way for other perovskite-based optoelectronic devices.