Efficiency and stability are the two most important factors in commercially scalable solar cells.

The luminescent properties of cycloplatinated complexes containing aryl and SMe ₂ ligands, [Pt( p -MeC ₆ H ₄ )(ĈN)(SMe ₂ )], (ĈN = benzo[ h ]quinolate (bzq), 1 , or 2-phenylpyridinate (ppy), 2 ), were investigated in solution and solid state.

Complexes [Pt(C^{^}N)(PPh₃)Cl] (C^{^}N = bzq (7,8-benzoquinolinyl, A) and ppy (2-phenylpyridinyl, B)) were reacted with various thiolate ligands to afford complexes [Pt(C^{^}N)(PPh₃)(κ¹-S-SR)], C^{^}N = bzq, R = SPh (thiophenolate, 1a); C^{^}N = ppy, R = SPh (1b); C^{^}N = bzq, R = Spy (pyridine-2-thiolate, 2a); C^{^}N = ppy, R = Spy (2b); C^{^}N = bzq, R = SpyN (pyrimidine-2-thiolate, 3a); C^{^}N = ppy, R = SpyN (3b). Complexes 1–3 were characterized by NMR spectroscopy, and the solid-state structures of 1a and 2a were determined by X-ray diffraction methods. Replacing a chloride ligand with electron-rich thiolates changes the lowest energy singlet and triplet excited states to the ones that feature charge transfer from the thiolate (mixed with some metal character) to the C^{^}N ligand, which was supported by TD-DFT calculations. All complexes are emissive at 298 K in the solid state except 2b and 3b, which are emissive only at 77 K having a less rigid structure compared to others. The emission of 1a and 1b originates from a low-energy excited state of d_Pt/π_SR → π*_C^N while 3a exhibits a ³LC/³MLCT transition. For 1a and 1b, the radiative rate and the quantum efficiency are higher in a rigid environment such as a solid compared to a polymer and solution. Decreasing the rigidity of the environment leads to a flexibility of rotation of the –SR around the axis of the Pt–S bond. So the geometry can be easily changed after radiation and the lowest lying triplet excited state would have the effective contribution of the dd* transition, which opens a nonradiative pathway at room temperature.

Heterobimetallic compounds [(C^N)LMe₂Pt(μ-O)ReO₃] (C^N = ppy, L = PPh₃, 2a; C^N = ppy, L = PMePh₂, 2b; C^N = bhq, L = PPh₃, 2c; C^N = bhq, L = PMePh₂, 2d) containing a discrete unsupported Pt(IV)–O–Re(VII) bridge have been synthesized through a targeted synthesis route. The compounds have been prepared by a single-pot synthesis in which the Pt(IV) precursor [PtMe₂I(C^N)L] complexes are allowed to react easily with AgReO₄ in which the iodide ligand of the starting Pt(IV) complex is replaced by an ReO₄ ⁻ anion. In these Pt–O–Re complexes, the Pt(IV) centers have an octahedral geometry, completed by a cyclometalated bidentate ligand (C^N), two methyl groups and a phosphine ligand, while the Re(VII) centers have a tetrahedral geometry. Elemental analysis, single crystal X-ray diffraction analysis and multinuclear NMR spectroscopy are used to establish their identities. The new complexes exhibit phosphorescence emission in the solid and solution states at 298 and 77 K, which is an uncommon property of platinum complexes with an oxidation state of +4. According to DFT calculations, we found that this emission behavior in the new complexes originates from ligand centered ³LC (C^N) character with a slight amount of metal to ligand charge transfer (³MLCT). The solid-state emission data of the corresponding cycloplatinated(IV) precursor complexes [PtMe₂I(C^N)L], 1a–1d, pointed out that the replacement of I⁻ by an ReO₄ ⁻ anion helps enhancing the emission efficiency besides shifting the emission wavelengths.

The pursuit of p-type semiconductors has garnered considerable attention in academia and industry. Among the potential candidates, copper iodide (CuI) stands out as a highly promising p-type material due to its conductivity, cost-effectiveness, and low environmental impact. CuI can be employed to create thin films with >80% transparency within the visible range (400–750 nm) and utilizing various low-temperature, scalable deposition techniques. This review summarizes the deposition techniques for CuI as a hole-transport material and their performance in perovskite solar cells, thin-film transistors, and light-emitting diodes using diverse processing methods. The preparation methods of making thin films are divided into two categories: wet and neat methods. The advancements in CuI as a hole-transporting material and interface engineering techniques hold promising implications for the continued development of such devices.