Narrow Band Gap Hybrid Copper(I)Iodides: Designer\nMaterials for Optoelectronic Applications

In\nrecent years, there has been a concerted effort in developing\nnarrow band gap semiconductors that exhibit excellent physical properties\nand optoelectronic performance, as well as enhanced solution processability\nand structural stability. Herein, we report a new series of copper(I)iodide-based\nionic hybrid semiconductors with narrow band gaps (∼1.5–1.8\neV). These compounds are systematically designed by using pyrazine\nderivatives as cationic ligands and various 1D-Cu<sub><i>m</i></sub>I<sub><i>n</i></sub> chains as anionic inorganic\nmotifs to form one-dimensional (1D) structures. They demonstrate high\noptical absorption coefficients, decent electrical conductivity, excellent\nair/moisture/thermal stability, and superb solution processability,\nenabling the fabrication of high-quality thin films via simple solution\nprocesses. Additionally, we have carried out a comprehensive photoelectron\nspectroscopic study on highly orientated thin film samples of selected\nhybrid compounds to experimentally verify, for the first time, that\nthe photoexcitation process in such materials involves an anion-to-cation\nthrough-space charge transfer (TSCT), consistent with the calculated\nelectronic structures. Overall, these narrow band gap CuI-based hybrid\nsemiconductors define a new subclass of low-cost, highly stable, and\nefficient light-absorbing materials promising for applications in\noptoelectronics.