Photosensitive Halide Semiconductors Enabled by Electron Reservoirs From Extended Viologens

Abstract Bismuth‐based organic–inorganic hybrid semiconductors have practical limitations in optoelectronic applications due to low carrier separation and collection efficiency. This study proposes an intramolecular carrier transfer strategy to enhance carrier separation by forming a type‐II heterojunction between the organic and inorganic components. Extended methyl viologens (eMVs) are used as the A‐site. Theoretical calculations and transient absorption analyses confirm electron transfer from the inorganic to the organic part. The organic cation acts as an electron reservoir, suppressing the recombination of photogenerated carriers and promoting separation and stabilization. In particular, modulating the heteroaromatic system improves the storage capacity of the electron reservoir and enhances its role in stabilizing carriers. Me 2 Py 2 TTzBi 2 I 8 exhibits excellent photoelectric responses, with an on/off ratio of 120 and high X‐ray sensitivity of up to 259 µC Gy air −1 cm −2 , with a low detection limit of 320 nGy air s −1 , indicating its potential application in detectors. Additionally, the π ‐conjugated cations protect the Bi─I octahedral chain from decomposition, enabling it to withstand harsh conditions such as water, acidity, and high/low temperatures. This work provides new ideas for designing organic cations in bismuth‐based hybrid semiconductors, which are expected to overcome the limitations of carrier collection and develop new, high‐performance materials.