Ultrafast Electron Dynamics in Solar Energy Conversion Carlito S. Ponseca, Jr., † Pavel Cha ́ bera, † Jens Uhlig, † Petter Persson, ‡ and Villy Sundströ m* ,† † Division of Chemical Physics, Chemical Center, and ‡ Theoretical Chemistry Division, Chemical Center, Lund University, Box 124, Lund SE-221 00, Sweden ABSTRACT: Electrons are the workhorses of solar energy conversion. Conversion of the energy of light to electricity in photovoltaics, or to energy-rich molecules (solar fuel) through photocatalytic processes, invariably starts with photoinduced generation of energy- rich electrons. The harvesting of these electrons in practical devices rests on a series of electron transfer processes whose dynamics and efficiencies determine the function of materials and devices. To capture the energy of a photogenerated electron-hole pair in a solar cell material, charges of opposite sign have to be separated against electrostatic attractions, prevented from recombining and being transported through the active material to electrodes where they can be extracted. In photocatalytic solar fuel production, these electron processes are coupled to chemical reactions leading to storage of the energy of light in chemical bonds. With the focus on the ultrafast time scale, we here discuss the light- induced electron processes underlying the function of several molecular and hybrid materials currently under development for solar energy applications in dye or quantum dot- sensitized solar cells, polymer-fullerene polymer solar cells, organometal halide perovskite solar cells, and finally some photocatalytic systems. CONTENTS 1. Introduction B 2. Experimental and Theoretical Methods C 2.1. General Experimental Considerations C 2.2. Time-Resolved Techniques D 2.2.1. Time-Resolved Optical Spectroscopy E 2.2.2. Time-Resolved Infrared Spectroscopy E 2.2.3. Time-Resolved THz Spectroscopy: Tran- sient Photoconductivity Measurements F 2.2.4. Time-Resolved X-ray Spectroscopy and Scattering F 2.3. Advanced and Emerging Experimental Char- acterization H 2.3.1. Coherent Control H 2.3.2. Multidimensional Spectroscopy J 2.3.3. Time-Resolved Microscopy J 2.3.4. Time-Resolved Spectroelectrochemistry J 2.4. Theoretical and Computational Considera- tions J 3. Solar Cell Technologies O 3.1. Dye-Sensitized Solar Cells O 3.1.1. Electron Injection from Sensitizer to Metal Oxide Acceptor O 3.1.2. Electron-Cation Recombination R 3.1.3. Formation of Mobile Charges U 3.1.4. Earth Abundant Metal-Based Photo- sensitizers V 3.1.5. Organic and Push-Pull Dyes X 3.2. Quantum Dot-Sensitized Solar Cells Z 3.2.1. Photoinduced Electron Injection Z 3.2.2. Multiple Exciton Generation AA 3.2.3. Charge Recombination in Quantum Dot-Metal Oxide Systems AC 3.3. Organic Solar Cells AD 3.3.1. Charge Generation AD 3.3.2. Charge Carrier Recombination AG 3.3.3. Carrier Photoconductivity and Mobility AH 3.4. Perovskite Solar Cells AL 3.4.1. From Carrier Generation to Recombina- tion AL 3.4.2. Ion Dynamics Influencing Carrier Dy- namics AN 3.4.3. Charge Carrier Transport and Mobility AP 3.4.4. Charge Carrier Dynamics of Perovskite/ Transport Layer Devices AR 3.4.5. Perovskite Single-Crystal Carrier Dynam- ics AS 3.4.6. Outlook for Organo-Metal Halide Perov- skites AT 3.5. Advanced and Emerging Solar Energy Technologies AU 3.5.1. Solid-State Nanomaterials AU 3.5.2. Molecular Antennas AU 3.5.3. Singlet Fission AU 3.5.4. Triplet-Triplet Annihilation Photon Up- conversion AW 4. Photocatalysis AW 4.1. Molecular Photocatalysis AX 4.1.1. Sensitizers AX Special Issue: Ultrafast Processes in Chemistry Received: December 1, 2016 Review pubs.acs.org/CR © XXXX American Chemical Society A DOI: 10.1021/acs.chemrev.6b00807 Chem. Rev. XXXX, XXX, XXX-XXX