**2. Dynamics of charge carriers in QD‐sensitized solar cells**

Semiconductor nanocrystals, so‐called quantum dots (QD), are confined quantum objects whose optoelectronic properties are dependent on their sizes [1]. Due to recent progress in chemical solution processing techniques for synthesis of colloidal QDs [2], it has attracted increasing attention on its fundamental properties [3] and applications [4]. The QDs can be utilized as imaging markers [5], as building blocks in light‐emitting diode devices, [6] lasers and light harvesters in solar cells devices [7, 8]. Particularly, the potential application in photovoltaic devices has become the focus of the field over the past decade. One of the reasons for this is the possibility of breaking the Shockley‐Queisser thermodynamic limit of single junction solar cells via multiple exciton generation (MEG) [9] or hot electron transfer (HET) [10]. Besides, the efficiencies of colloidal QD‐based solar cells have been rapidly improving [11]. In this work, we would only discuss colloidal QDs and would refer it simply as QD. The recent progress in the understanding of the photo‐induced dynamic processes in QD‐based solar cell components is summarized in this section. Electron injection dynamics in QD—metal oxide (MO) composites is investigated followed by the studies of hole transfer dynamics and trapping. We also analyze excitation transfer in the films of QDs. The article is mainly based on the studies of Cadmium chalcogenide QDs as well as some progress made for systems such as lead chalcogenide QDs in solar cell application.
