Lessons Learned: From Dye‐Sensitized Solar Cells to All‐Solid‐State Hybrid Devices

The field of solution‐processed photovoltaic cells is currently in its second spring. The dye‐sensitized solar cell is a widely studied and longstanding candidate for future energy generation. Recently, inorganic absorber‐based devices have reached new record efficiencies, with the benefits of all‐solid‐state devices. In this rapidly changing environment, this review sheds light on recent developments in all‐solid‐state solar cells in terms of electrode architecture, alternative sensitizers, and hole‐transporting materials. These concepts are of general applicability to many next‐generation device platforms.     

Carbon Nanotubes for Dye‐Sensitized Solar Cells

As one type of emerging photovoltaic cell, dye‐sensitized solar cells (DSSCs) are an attractive potential source of renewable energy due to their eco–friendliness, ease of fabrication, and cost effectiveness. However, in DSSCs, the rarity and high cost of some electrode materials (transparent conducting oxide and platinum) and the inefficient performance caused by slow electron transport, poor light‐harvesting efficiency, and significant charge recombination are critical issues. Recent research has shown that carbon nanotubes (CNTs) are promising candidates to overcome these issues due to their unique electrical, optical, chemical, physical, as well as catalytic properties. This article provides a comprehensive review of the research that has focused on the application of CNTs and their hybrids in transparent conducting electrodes (TCEs), in semiconducting layers, and in counter electrodes of DSSCs. At the end of this review, some important research directions for the future use of CNTs in DSSCs are also provided.     

Metal Oxide Semiconductors for Dye‐ and Quantum‐Dot‐Sensitized Solar Cells

This Review provides a brief summary of the most recent research developments in the synthesis and application of nanostructured metal oxide semiconductors for dye sensitized and quantum dot sensitized solar cells. In these devices, the wide bandgap semiconducting oxide acts as the photoanode, which provides the scaffold for light harvesters (either dye molecules or quantum dots) and electron collection. For this reason, proper tailoring of the optical and electronic properties of the photoanode can significantly boost the functionalities of the operating device. Optimization of the functional properties relies with modulation of the shape and structure of the photoanode, as well as on application of different materials (TiO₂, ZnO, SnO₂) and/or composite systems, which allow fine tuning of electronic band structure. This aspect is critical because it determines exciton and charge dynamics in the photoelectrochemical system and is strictly connected to the photoconversion efficiency of the solar cell. The different strategies for increasing light harvesting and charge collection, inhibiting charge losses due to recombination phenomena, are reviewed thoroughly, highlighting the benefits of proper photoanode preparation, and its crucial role in the development of high efficiency dye sensitized and quantum dot sensitized solar cells.     

Edge‐Functionalized Graphene Nanoplatelets as Metal‐Free Electrocatalysts for Dye‐Sensitized Solar Cells

A scalable and low‐cost production of graphene nanoplatelets (GnPs) is one of the most important challenges for their commercialization. A simple mechanochemical reaction has been developed and applied to prepare various edge‐functionalized GnPs (EFGnPs). EFGnPs can be produced in a simple and ecofriendly manner by ball milling of graphite with target substances (X = nonmetals, halogens, semimetals, or metalloids). The unique feature of this method is its use of kinetic energy, which can generate active carbon species by unzipping of graphitic C? C bonds in dry conditions (no solvent). The active carbon species efficiently pick up X substance(s), leading to the formation of graphitic C? X bonds along the broken edges and the delamination of graphitic layers into EFGnPs. Unlike graphene oxide (GO) and reduced GO (rGO), the preparation of EFGnPs does not involve toxic chemicals, such as corrosive acids and toxic reducing agents. Furthermore, the prepared EFGnPs preserve high crystallinity in the basal area due to their edge‐selective functionalization. Considering the available edge X groups that can be selectively employed, the potential applications of EFGnPs are unlimited. In this context, the synthesis, characterizations, and applications of EFGnPs, specifically, as metal‐free carbon‐based electrocatalysts for dye‐sensitized solar cells (DSSCs) in both cobalt and iodine electrolytes are reviewed.