Dye‑sensitized solar cells (DSSCs): Sensitizers engineering design, photophysical principles, and strategies for improvement of energy conversion efficiency – A review

Abstract

This review examines the fundamental principles guiding the photovoltaic solar energy conversion and the current state of research on dye-sensitized solar cells (DSSCs) as a promising third-generation technology for environmentally sustainable energy applications. Particular attention is given to the dye sensitizer as the key component of DSSCs, governing the spectral response, the efficiency of electron injection into nanostructured TiO2 as semiconductor, and the long-term stability of the device. The review summarizes the characteristics of the three major classes of sensitizers: ruthenium complexes, metal-free organic donor–π–acceptor (D–π–A) dyes based on triphenylamine, and the natural pigments, including anthocyanins, betalains, chlorophylls, and carotenoids. The optical absorption properties, HOMO/LUMO energy levels, photostability, and adsorption behavior on TiO2 surfaces are comparatively analyzed. Ruthenium complexes remain the benchmark sensitizers, achieving power conversion efficiencies (PCEs) of approximately 10–14%, whereas organic triphenylamine (TPA)-based dyes exhibit comparable performance while offering greater structural tunability and lowering of potential toxicity. In contrast, natural dyes still suffer from relatively low efficiencies due to their narrow absorption spectra and limited photochemical stability. Recent strategies for improving DSSC performance are also discussed, including co-sensitization, cobalt- and copper-based redox mediators, TiO2 nanostructuring, D–A–π–A molecular architectures, and the integration of metal–organic frameworks (MOFs). Finally, the major barriers to DSSC commercialization are highlighted, together with promising application areas such as indoor photovoltaics, the Internet of Things (IoT), building-integrated photovoltaics (BIPV), agrivoltaics, and the development of environmentally benign photovoltaic systems.