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

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In many photovoltaics (PVs), including dye‐sensitized solar cells (DSSCs), triiodide/iodide (I 3 − /I − ) redox couple plays an important role, and an active and stable electrocatalyst is required for promoting I 3 − 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 LaNiO 3 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 LaNiO 3 with carbon material is applied for the facile synthesis of LaNiO 3 /carbon composites. This ball‐milling process simultaneously leads to partial reduction of LaNiO 3 by carbon with the creation of oxygen vacancies inside the perovskite oxide lattice, a decrease in LaNiO 3 particle size and the creation of strong coupling between LaNiO 3 and carbon. Particularly, DSSC with LaNiO 3 /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. LaNiO 3 or carbon alone demonstrates a much poorer performance. Moreover, LaNiO 3 /carbon composites demonstrate excellent operational stability. This study highlights the extended applications of perovskites in other I 3 − /I − ‐mediated PVs, electrochromic devices or batteries.