**1. Introduction**

The emergence of different photovoltaic technologies has been driven by the desire to find an alternative solar cell technology that can be manufactured using simple laboratory processes

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

and at lower cost. This has led to conceptualization and development of hybrid solar cells, a structure where an organic molecule is usedas light absorber andthen attached to a metal oxide (MO). The earliest of this type is the dye‐sensitized solar cell also known as the Graetzel‐type solar cell. Upon light excitation, the dye generate excitons wherein electrons are injected into metaloxide(usuallyTiO2)whileholestraverseinliquidiodineelectrolyte.Thisfieldhasbranched outto many material substitutions,two of which will be discussed in this chapter. On one hand, organic dyes were replaced by quantum dots, whose absorption spectra highly depends on its miniscule size, have now reached an overall power conversion efficiency (PCE) of 11.3% accordingtothesolar cellefficiencychartoftheNationalRenewableEnergyLaboratory(NREL), USA. On the other hand, organo‐metal halide perovskite solar cells adopt a perovskite crystal structure (usually orthorhombic), but has organic molecules, e.g., methyl ammonium, within its unit cell. Since its first discovery about 6 years ago, it has become one of the most serious competitors of silicon solar cells having a PCE 22.1% (NREL).

In this chapter, we present the ultrafast charge dynamics of these materials from the subpico‐ second (ps) to a nanosecond (ns) time scale. Using transient spectroscopy techniques, the evolution of the charges from photoexcitation to recombination will be discussed. This chapter is divided into two main sections. First, results on quantum dot (QD) sensitized solar cell will be presented. This will include the electron injection in an *n*‐type metal oxide (MO) acceptor as well as the hole injection to a p‐type MO. The influence of single layer and multiple layers of QD on excitation transfer will be also examined. The second section will focus on the nature of photogenerated charges in organo‐metal halide perovskite (OMHP), mobility and lifetime of charge carriers, and the mechanism and time scale of charge injection from perovskite material to organic electrodes.
