Photocathodes In Dye-sensitized Solar Cells Research Articles

Electrochemically Synthesized Mesoscopic Nickel Oxide Films as Photocathodes for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) have been considered as promising and reliable solar energy conversion devices that are suitable for various applications. In general, mesoscopic TiO2 films are of...

Rational Design of LaNiO3/Carbon Composites as Outstanding Platinum‐Free Photocathodes in Dye‐Sensitized Solar Cells With Enhanced Catalysis for the Triiodide Reduction Reaction

In many photovoltaics (PVs), including dye‐sensitized solar cells (DSSCs), triiodide/iodide (I3−/I−) redox couple plays an important role, and an active and stable electrocatalyst is required for promoting I3− reduction reaction (IRR) to minimize efficiency losses. Platinum (Pt) is the state‐of‐the‐art electrocatalyst for IRR, which unfortunately suffers from high cost and poor stability. Herein, strongly coupled LaNiO3 perovskite/carbon composites are developed for the first time as highly efficient, stable and low‐cost electrocatalysts for IRR to enable better DSSCs. High‐energy ball milling of crystallized LaNiO3 with carbon material is applied for the facile synthesis of LaNiO3/carbon composites. This ball‐milling process simultaneously leads to partial reduction of LaNiO3 by carbon with the creation of oxygen vacancies inside the perovskite oxide lattice, a decrease in LaNiO3 particle size and the creation of strong coupling between LaNiO3 and carbon. Particularly, DSSC with LaNiO3/multi‐walled carbon nanotubes photocathode delivers a high power conversion efficiency of 9.81% with an attractive enhancement of 21% compared with Pt electrocatalyst, superior to most state‐of‐the‐art highly efficient Pt‐free photocathodes in DSSCs. LaNiO3 or carbon alone demonstrates a much poorer performance. Moreover, LaNiO3/carbon composites demonstrate excellent operational stability. This study highlights the extended applications of perovskites in other I3−/I−‐mediated PVs, electrochromic devices or batteries.

Hierarchically-Structured NiO Nanoplatelets as Mesoscale p-Type Photocathodes for Dye-Sensitized Solar Cells

A p-type metal oxide with high surface area and good charge carrier mobility is of paramount importance for development of tandem solar fuel and dye-sensitized solar cell (DSSC) devices. Here, we report the synthesis, hierarchical morphology, electrical properties, and DSSC performance of mesoscale p-type NiO platelets. This material, which exhibits lateral dimensions of 100 nm but thicknesses less than 10 nm, can be controllably functionalized with a high-density array of vertical pores 4–6, 5–9, or 7–23 nm in diameter depending on exact synthetic conditions. Thin films of this porous but still quasi-two-dimensional material retain a high surface area and exhibit electrical mobilities more than 10-fold higher than comparable films of spherical particles with similar doping levels. These advantages lead to a modest, 20–30% improvement in the performance of DSSC devices under simulated 1-sun illumination. The capability to rationally control morphology provides a route for continued development of NiO as a...

Coumarin 343−NiO Films as Nanostructured Photocathodes in Dye-Sensitized Solar Cells: Ultrafast Electron Transfer, Effect of the I3−/I− Redox Couple and Mechanism of Photocurrent Generation

Nanoporous, p-type NiO films were sensitized with coumarin 343 (C343), and the photoinduced electron transfer dynamics was studied in the presence of different concentrations of electrolyte (I3−/I− in propylene carbonate). Electron transfer from the valence band of NiO to the excited C343 is very fast, occurring on time scales from hundreds of femtoseconds to a few picoseconds, but also the subsequent recombination is quite rapid, on the time scale of tens of picoseconds. Nevertheless, formation of an intermediate, attributed to I2−| NiO(+), was observed on the picosecond time scale. Simultaneously the reduced dye was converted back to the C343 ground state, indicating that recombination could be intercepted by I3− reduction. Consistent with that interpretation, we observed oxidized NiO and depletion of I3− persisting on the millisecond time scale. Complete dye-sensitized solar cells (DSSCs) with these films as photocathode gave up to 10−11% incident photon to current conversion efficiency at the C343 vis...

Photoinduced Ultrafast Dynamics of Coumarin 343 Sensitized p-Type-Nanostructured NiO Films

Photoinduced electron transfer from the valence band of nanocrystalline NiO, a p-type semiconductor, to an excited bound dye, coumarin 343, and the subsequent recombination have been measured by femtosecond transient absorbance spectroscopy probing with white light. It was found that both processes are nonexponential. The photoinduced electron transfer from the semiconductor to the excited bound dye has an ultrafast component (approximately 200 fs), which is comparable to the time constants measured for photoinduced electron injection in C343-TiO2 colloid solutions. The process is very efficient and constitutes the main path of deactivation of the excited dye. Back electron transfer is also remarkably fast, with the main part of the recombination process happening with a time constant of approximately 20 ps. Dye-sensitized nanostructured p-type semiconductors are attractive materials due to their potential use as photocathodes in dye-sensitized solar cells and solid electrolytes in solid-state dye-sensitized solar cells. To our knowledge, this is the first time that the photoinduced electron-transfer kinetics of a sensitized p-type semiconductor has been studied.