Organic-inorganic perovskite solar cells containing various device structures (mesoporous, planar and inverted structured), which origin from conventional dye sensitized solar cells (DSSCs), have surged great waves in photovoltaic field owing to their peculiar advantages. However, comparing with the relatively mature development of charge carrier recombination research in DSSCs, the related studies are still on the initial stage in perovskite solar cells. The most accepted charge carrier recombination mechanism of trap-limited charge carrier recombination in DSSCs is not suitable for perovskite solar cells, especially the mesoporous structured perovskite solar cells, which has the most similar device structure with DSSCs. In our work, conventional DSSCs and mesoporous structured perovskite solar cells were prepared and their charge carrier recombination properties were measured and investigated by transient photovoltage decay method. In DSSCs the charge carrier recombination process is predominated by the trap states in mesoporous TiO₂ phase, and thus, leading to a mono-exponential recombination decay process. However, in mesoporous structured perovskite solar cells, we found that the perovskite phase also plays a crucial role in charge carrier recombination process, i.e., at low Fermi level, photo-generated electrons predominately populate in perovskite phase, while at high Fermi level, most electrons occupy traps in mesoporous TiO₂. As a result, the dynamics of charge carrier recombination is respectively dominated by perovskite phase and mesoporous TiO₂ in these two cases.¹ Further investigation suggests that the demarcation voltage between perovskite-dominated and TiO₂-dominated recombination process is influenced by the trap state distribution & density of perovskite.² Recently, a physical model based on multiple trap theory is proposed by taking into account both the contributions of perovskite phase and mesoporous TiO₂ phase, which is suitable to describe the biphasic charge carrier recombination process in mesoporous structured perovskite solar cells.³ These findings provide a novel horizon for the understanding of the charge carrier recombination process in perovskite solar cells.  

1. H. Y. Wang, Y. Wang, M. Yu, J. Han, Z. X. Guo, X. C. Ai, J. P. Zhang and Y. Qin, Phys. Chem. Chem. Phys., 2016, 18, 12128-12134.

2. H. Y. Wang, M. Y. Hao, J. Han, M. Yu, Z. X. Guo, P. Zhang, Y. Qin, X. C. Ai, J. P. Zhang, Under review.

3. H. Y. Wang, Y. Wang, M. Y. Hao, J. Han, M. Yu, Z. X. Guo, P. Zhang, Y. Qin, X. C. Ai, J. P. Zhang, In preparation.