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Solar cells made up of lead-halide perovskites have shown a remarkable increase in power conversion efficiency; however, they are plagued with instability issues that, combined with the toxicity of lead, have led to a search for new semiconductors made up of heavy and nontoxic metals such as bismuth. Here, we report on a new, inorganic, double perovskite oxide semiconductor: KBaTeBiO 6 , which has an experimental indirect band gap of 1.88 eV and shows excellent stability. We combined data analytics and high throughput density functional theory calculations to search through thousands of hypothetical inorganic double perovskite oxides containing bismuth and predict KBaTeBiO 6 as a potential photovoltaic material, which was subsequently synthesized using a wet-chemistry route. The calculated effective mass of the charge carriers for KBaTeBiO 6 is comparable to the best performing Bi-halide double perovskites. Our work demonstrates the untapped potential of inorganic Bi-based double perovskite oxidesthat offer the ability to change both the cation combination and their stoichiometry to achieve desired electronic propertiesas exciting, benign, and stable alternatives to lead-halide perovskites for various semiconducting applications.

Dye-sensitized solar cells (DSSCs) serve as low-costing alternatives to silicon solar cells because of their low material and fabrication costs. Usually, they utilize Pt as the counter electrode (CE) to catalyze the iodine redox couple and to complete the electric circuit. Given that Pt is a rare and expensive metal, various carbon materials have been intensively investigated because of their low costs, high surface areas, excellent electrochemical stabilities, reasonable electrochemical activities, and high corrosion resistances. In this feature article, we provide an overview of recent studies on the electrochemical properties and photovoltaic performances of carbon-based CEs (e.g., activated carbon, nanosized carbon, carbon black, graphene, graphite, carbon nanotubes, and composite carbon). We focus on scientific challenges associated with each material and highlight recent advances achieved in overcoming these obstacles. Finally, we discuss possible future directions for this field of research aimed at obtaining highly efficient DSSCs.

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