**4. Conclusion**

Ultrafast time‐resolved studies of two of the most important hybrid solar cell technologies, quantum dot‐sensitized and perovskite‐based solar cells, were discussed in this chapter. The mechanism and time scale of charge generation, nature of charged species, mobility, injection, and recombination were obtained using transient absorption, photoluminescence, and photoconductivity measurements. For quantum dot‐sensitized solar cell materials, electron injection is a two‐step process; first, a few ps injection at the interface between QD and ZnO, while the second step is a charge transfer state‐mediated 200 ps injection from the interface to the bulk of the ZnO material. For multiple layers of QDs, excitation transfer is confirmed while hole injection is shown to be dictated by the band alignment at the interface but limited by fast hole trapping. For organo‐metal halide perovskite, almost ideal solar cell characteristics were found, i.e., ultrafast generation charges, high mobility of electrons and holes that is maintained for at least 1 ns, and balanced transport. Using organic electrodes, electron injection from perovskite to PCBM is found to be in the sub‐ns while the sub‐ps hole injection is obtained from perovskite to Spiro‐OMeTAD. The time scale of charge transfer was found to be depend‐ ent on the driving force between the interface of perovskite and organic electrodes. Despite the seemingly convincing time‐resolved measurement results, we surmise that more thorough investigations are warranted. This is in the broader context of further understanding the influence of preparation conditions to the ultrafast charge carrier dynamics of the solar cell technologies discussed here.
