Bulk Heterojunction Perovskite Solar Cells Incorporated with Zn₂SnO₄ Nanoparticles as the Electron Acceptors

Perovskite solar cells were developed very fast in the past decade, but hybrid perovskite materials with unbalanced charge carrier diffusion lengths were not fully addressed by either conventional or planar heterojunction device structures. In this study, high-performance perovskite solar cells with bulk heterojunction device structures where CH₃NH₃PbI_2.55Br_0.45 is blended with an n-type high-electron-mobility Zn₂SnO₄ nanoparticle as the photoactive layer are reported. Systematic studies indicate that the CH₃NH₃PbI_2.55Br_0.45:Zn₂SnO₄ bulk heterojunction thin film possesses enhanced and balanced charge carrier mobilities, superior film morphology with enlarged crystal sizes, and suppressed trap density. Photoluminescence and time-resolved photoluminescence studies further demonstrate that there is an efficient photoinduced charge carrier transfer between CH₃NH₃PbI_2.55Br_0.45 and Zn₂SnO₄ nanoparticles. Thus, bulk heterojunction perovskite solar cells by the CH₃NH₃PbI_2.55Br_0.45:Zn₂SnO₄ thin film exhibit over 21.07% power conversion efficiency, which is more than 12% enhancement as compared to that (18.74%) observed from planar heterojunction perovskite solar cells by the pristine CH₃NH₃PbI_2.55Br_0.45 thin film. Moreover, bulk heterojunction perovskite solar cells possess significantly suppressed photocurrent hysteresis, dramatically enhanced device stability, and reproducibility. All these results demonstrate that high-performance perovskite solar cells can be realized through bulk heterojunction device structures.