Prof Henry Snaith FRS

Abstract:

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. The field of solution-processed photovoltaic cells is currently in its second spring, with solid-state devices incorporating novel inorganic absorbers reaching record efficiencies. This review sheds light on recent developments in all-solid-state solar cells in terms of electrode architecture, alternative sensitizers, and hole-transporting materials: concepts applicable to many next-generation device platforms. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Abstract:

The solid-state dye-sensitized solar cell (DSSC) was introduced to overcome inherent manufacturing and instability issues of the electrolyte-based DSSC and progress has been made to deliver high photovoltaic efficiencies at low cost. However, despite 15 years research and development, there still remains no clear demonstration of long-term stability. Here, solid-state DSSCs are subjected to the severe aging conditions of continuous illumination at an elevated temperature. A fast deterioration in performance is observed for devices encapsulated in the absence of oxygen. The photovoltaic performance recovers when re-exposed to air. This reversible behavior is attributed to three related processes: i) the creation of light and oxygen sensitive electronic shunting paths between TiO2 and the top metal electrode, ii) increased recombination at the TiO2/organic interface, and iii) the creation of deep electron traps that reduce the photocurrent. The device deterioration is remedied by the formation of an insulating alumino-silicate shell around the TiO2 nanocrystals, which reduces interfacial recombination, and the introduction of an insulating mesoporous SiO2 buffer layer between the top electrode and TiO2, which acts as a permanent insulating barrier between the TiO2 and the metal electrode, preventing shunting. Encapsulated solid-state dye-sensitized solar cells (ssDSSCs) show a reversible and quick deterioration in performance while aging under inert atmosphere. This is attributed to the activation of deep traps and the change in Schottky barrier at the TiO2 surface. This is remedied by forming an insulating alumino-silicate "shell" around the TiO2 nanocrystals, and by introducing an insulating mesoporous SiO2 "buffer layer" between the top electrode and TiO2. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.