**Acknowledgements**

preparation conditions yield different film quality manifesting as different values in their mobility, among other properties. As to the flat transient photoconductivity trace of this sample, it can be understood such that electrons remain in the perovskite material and did not encounter either defects where they can be trapped or holes which they can recombine with.

The transient photoconductivity trace of MAPbI3/PCBM is characterized by mobility similar

implies that both electrons and holes are generated in the perovskite. The decay could then be assigned as due to second order geminate recombination. However, this type of recombination is excitation dependent. If this is the case, both the transient photoconductivity of MAPbI3 and MAPbI3/Spiro‐OMeTAD should also be decaying at the same rate since the excitation fluence used for these three samples are the same. Since this is not the case, one can discount this possibility. In addition and as shown in **Figure 6(b)**, where a higher excitation fluence is used for MAPbI3 and MAPbI3/PCBM but for a longer time window of 7 ns, the decay in MAPbI3/ PCBM is faster than MAPbI3 only, showing that there is an additional mechanism that causes the decay other than the second order recombination. It has been reported that the energy difference between the conduction bands of PCBM and perovskite is only 0.2 eV. As such, injection is still possible, but unlike in perovskite/Spiro‐OMeTAD interface, this injection can be slower since the driving force is at least two times less. This slower injection rate of electrons from perovskite to PCBM could be one of the mechanisms of the decay. Furthermore, one

implies that while electrons are slowly injecting into the PCBM, the low mobility of the PCBM causes the electrons to be pinned at the interface. In this scenario, holes that are in perovskite could easily recombine with the electrons pinned at the interface of PCBM which could also have a ns time scale. We surmised that the ns decay of the transient photoconductivity shown in **Figure 6** is a convolution of the electron injection and recombination of the pinned electrons at the interface with the holes left in the perovskite material both occuring in the time scale of

There are many studies that have reported the very impressive properties of perovskite‐based solar cells and these have inspired material scientists and engineers to pursue this field of study. However, this should be taken as only the start of a longer, more detailed investigations in the future. It is only very recently that evidence of the influence of preparation conditions is getting the attention it deserves. In organic solar cells, preparation routes dictate the morphology, therefore, the quality of the film, which now appear to be very similar to perovskite solar cells.

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,

should also take into account the electron mobility in PCBM, which is 10‐3 cm2

/Vs, but is decaying to almost a third in 1 ns. The initial value of the mobility

/Vs [51–55]. This

to MAPbI3, 15 cm2

128 Nanostructured Solar Cells

few ns.

**3.3. Outlook**

**4. Conclusion**

This work was supported by the Swedish Energy Agency, the Knut and Alice Wallenberg Foundation, and the Swedish Research Council. Collaboration within nanoLund and Lund Laser Center is acknowledged. We also acknowledge support from by NPRP grant # NPRP7‐ 227‐1‐034 from the Qatar National Research Fund (a member of Qatar Foundation) and Laserlab‐Europe (EU‐H2020 654148).
