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Despite the rapid progress in solar power conversion efficiency of archetype organic–inorganic hybrid perovskite CH₃NH₃PbI₃-based solar cells, the long-term stability and toxicity of Pb remain the main challenges for the industrial deployment, leading to more uncertainties for global commercialization. The poor stabilities of CH₃NH₃PbI₃-based solar cells may not only be attributed to the organic molecules but also the halides themself, most of which exhibit intrinsic instability under moisture and light. As an alternative, the possibility of oxide perovskites for photovoltaic applications is explored here. The class of lead-free stable oxide double perovskites A₂M(III)M(V)O₆ (A = Ca, Sr, Ba; M(III) = Sb³⁺ or Bi³⁺; M(V) = V⁵⁺, Nb⁵⁺, or Ta⁵⁺) is comprehensively explored with regard to their stability and their electronic and optical properties. Apart from the strong stability, this class of double perovskites exhibits direct bandgaps ranging from 0.3 to 3.8 eV. With proper B site alloying, the bandgap can be tuned within the range of 1.0–1.6 eV with optical absorptions as strong as CH₃NH₃PbI₃, making them suitable for efficient single-junction thin-film solar cell application.

The class of lead-free stable oxide double perovskites A₂M(III)M(V)O₆ (A = Ca, Sr, Ba; M(III) = Sb³⁺ or Bi³⁺; M(V) = V⁵⁺, Nb⁵⁺, or Ta⁵⁺) is comprehensively explored with regard to their stability and their electronic and optical properties. Apart from the strong stability, this class of double perovskites exhibits direct bandgaps ranging from 0.3 to 3.8 eV. With proper B site alloying, the bandgap can be tuned within the range of 1.0–1.6 eV with strong optical absorptions, making them suitable for efficient single-junction thin-film solar cell application.

Transition metal phosphorus trichalcogenides (MPX₃, X = S, Se) are layered materials possessing high chemical diversity and wide range of applications in a broad wave length spectrum. Theoretical studies reveal that auspicious activity of photocatalytic water splitting can be realized from them. However, experimental efforts have so far been challenged with the synthesis bottleneck. Described herein is the general chemical vapor deposition (CVD) growth method and photocatalytic activity of these materials. A novel route to systematically grow MnPX₃ nanosheets on flexible carbon fiber substrate is reported. The temperature profile of the CVD process is carefully optimized that confer a facile and successful conversion of oxide precursor to phospho-trichalcogenide with high crystallinity. Moreover, the obtained manganese-based phosphorus trichalcogenide nanosheets demonstrate promising activity in sacrificial agent-free photocatalytic water splitting under simulated solar light (AM 1.5G). This study provides a significant stepping stone in exploring the fascinating world of functional 2D materials and pursuing performance enhancement.

High crystal quality manganese-based transition metal phosphorus trichalcogenide nanosheets are synthesized facilely through chemical vapor deposition method. This novel route results in a successful synthesis of monoclinic MnPS₃ and hexagonal MnPSe₃ nanosheets with high phase purity. The obtained materials demonstrate promising photocatalytic activity of water splitting in pure water without cocatalyst.