Ternary bismuth halides form an interesting functional materials class in the context of the closely related Pb halide perovskite photovoltaics, especially given the significantly reduced toxicity of Bi when compared with Pb. The compounds A3Bi2I9 (A = K, Rb, Cs) examined here crystallize in two different structure types: the layered defect-perovskite K3Bi2I9 type, and the Cs3Cr2Cl9 type. The latter structure type features isolated Bi2I93– anions. Here, the crystal structures of the ternary iodides are redetermined and a corrected structural model for Rb3Bi2I9, as established by single crystal X-ray diffraction and solid state 87Rb NMR spectroscopy and supported by density functional theory (DFT) calculations is presented. A variety of facile preparation techniques for single crystals, bulk materials, as well as solution-processed thin films are described. The optical properties and electronic structures are investigated experimentally by optical absorption and ultraviolet photoemission spectroscopy and c...

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Crystal and Electronic Structures of Complex Bismuth Iodides A3Bi2I9 (A = K, Rb, Cs) Related to Perovskite: Aiding the Rational Design of Photovoltaics

Organic solar cells (OSCs) have shown great promise as low-cost photovoltaic devices for solar energy conversion over the past decade. Interfacial engineering provides a powerful strategy to enhance efficiency and stability of OSCs. With the rapid advances of interface layer materials and active layer materials, power conversion efficiencies (PCEs) of both single-junction and tandem OSCs have exceeded a landmark value of 10%. This review summarizes the latest advances in interfacial layers for single-junction and tandem OSCs. Electron or hole transporting materials, including metal oxides, polymers/small-molecules, metals and metal salts/complexes, carbon-based materials, organic-inorganic hybrids/composites, and other emerging materials, are systemically presented as cathode and anode interface layers for high performance OSCs. Meanwhile, incorporating these electron-transporting and hole-transporting layer materials as building blocks, a variety of interconnecting layers for conventional or inverted tandem OSCs are comprehensively discussed, along with their functions to bridge the difference between adjacent subcells. By analyzing the structure–property relationships of various interfacial materials, the important design rules for such materials towards high efficiency and stable OSCs are highlighted. Finally, we present a brief summary as well as some perspectives to help researchers understand the current challenges and opportunities in this emerging area of research.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201500362

Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives.

https://pubs.rsc.org/en/content/articlepdf/2017/cc/c6cc06475b

Beyond methylammonium lead iodide: prospects for the emergent field of ns2 containing solar absorbers

AgBiS2 nanocrystals offer a route to solution-processed environmentally friendly solar cells.

Solution-processed solar cells based on environmentally friendly AgBiS2 nanocrystals

Lead-based perovskites show very promising properties for use in solar cells; however, the toxicity of lead is a potential inhibitor for large-scale application of these solar cells. Here, a low-toxic bismuth halide, CsBi3I10, is synthesized from solution and the optical properties and crystal structure are compared with previously reported Cs3Bi2I9 perovskite, and the photovoltaic properties are also investigated. The XRD pattern suggests that the CsBi3I10 film has a layered structure with a different dominating crystal growth direction than the Cs3Bi2I9 perovskite. A band gap of 1.77 eV is obtained for the CsBi3I10 film, which is smaller than the band gap of Cs3Bi2I9 at 2.03 eV, and an extended visible light absorption spectrum is therefore obtained. The solar cell device with CsBi3I10 shows a photocurrent up to 700 nm, and this work shows therefore the possibility for increased light absorption and higher photocurrents in solar cells based on bismuth halide perovskites.

Extended Photo-Conversion Spectrum in Low-Toxic Bismuth Halide Perovskite Solar Cells.

https://www.phys.sinica.edu.tw/~lowtemp/publication/2013%20SEMSC%20organic%20solar%20cell.pdf

Solution-processable bismuth iodide nanosheets as hole transport layers for organic solar cells

A series of Sn added TiS2 (TiS2:Sn
 x
 ; x = 0, 0.05, 0.075 and 0.1) were prepared by solid state synthesis with subsequent annealing. The Sn atoms interacted with sulfur atoms in TiS2 and formed a trace amount of misfit layer (SnS)1+m(TiS2−δ)n compound with sulfur deficiency. A significant reduction in electrical resistivity with moderate decrease in the Seebeck coefficient was observed in Sn added TiS2. Hence, a maximum power factor of 1.71 mW/m-K2 at 373 K was obtained in TiS2:Sn0.05. In addition, the thermal conductivity was decreased with Sn addition and reached a minimum value of 2.11 W/m-K at 623 K in TiS2:Sn0.075, due to the impurity phase (misfit phase) and defects (excess Ti) scattering. The zT values increased from 0.08 in pristine TiS2 to an optimized value of 0.46 K at 623 K in TiS2:Sn0.05.

Sankar Raman

Papers

Solution-processable bismuth iodide nanosheets as hole transport layers for organic solar cells

Enhancement in Thermoelectric Properties of TiS 2 by Sn Addition

Effect of Hydrostatic Pressure on Transport, Magnetic and Superconducting Properties of Fe1.09se0.55te0.45