of which are necessary for the successful commercialization of sensitized solar cell (SSC).This report discusses recent progress in using ALD (and MLD) films (red in Table 1) for SSCs, including DSSCs, quantum dot-sensitized solar cells, solid (quasi)-state dye-sensitized solar cells, and perovskite-sensitized solar cells. The first three sections address how ALD can be used to manipulate charge transport in the photoanode, including the creation of core-shell semiconducting scaffolds and the conformal deposition of electrically insulating blocking to control electronic recombination. The next section focuses on synthesizing novel semiconducting scaffolds by ALD to effectively manipulate incident light and charge transport. Next this report describes how ALD can be used to create efficient and stable sensitizers. The final section discusses how ALD can favorably improve cathode materials, especially for electrocatalytic systems.
Manipulation of Charge TransportSince the seminal demonstration of O'Regan and Grätzel in the early 1990s, [4] m-TiO 2 (mesoporous TiO 2 ) has become the standard nanostructured semiconducting scaffold of choice for DSSCs. A 10 μm thick m-TiO 2 layer can have a net surface area exceeding 1000× the area of the projected planar surface. Once sensitized, the high surface area of m-TiO 2 permits sufficient light absorption to achieve >10% light-to-electric conversion efficiency. [5] As the efficiencies continue to increase and approach their theoretical limit, more effort is being placed on reducing performance losses across various DSSC interfaces. Major performance losses occur due to charge recombination at the semiconductor/electrolyte and semiconductor/fluorinedoped tin oxide (FTO) interfaces. ALD/MLD has been used to modify these interfaces to both understand fundamental electronic transport phenomena and improve device performance. In the following three subsections, we discuss the use of ALD/ MLD films for manipulating charge transfer kinetics in photoanodes for enhancing overall electron collection efficiency.
Core-Shell StructuresCore-shell assemblies are used in DSSCs to manipulate electron transfer processes across the sensitizer/semiconductor interface. Initial demonstrations of core-shell assemblies were Atomic layer deposition (ALD) and molecular layer deposition (MLD) are vapor phase deposition techniques used to create conformal coatings with molecular-level control of thickness and composition. Recently, ALD and MLD have been extensively exploited to engineer the complex interfaces of dye-sensitized solar cells (DSSCs) and other molecularly functionalized photoelectrochemical devices to improve the performance and long-term stability. This progress report describes the recent advances in the applications of ALD and MLD for sensitized solar cells including DSSCs then discusses current challenges and future opportunities of ALD.