RESUMO
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 CH3NH3PbI2.55Br0.45 is blended with an n-type high-electron-mobility Zn2SnO4 nanoparticle as the photoactive layer are reported. Systematic studies indicate that the CH3NH3PbI2.55Br0.45: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 CH3NH3PbI2.55Br0.45 and Zn2SnO4 nanoparticles. Thus, bulk heterojunction perovskite solar cells by the CH3NH3PbI2.55Br0.45: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 CH3NH3PbI2.55Br0.45 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.