Low-cost Narrow-Bandgap Organic Semiconductor for Efficient Photovoltaic and Photodetection Applications

Narrow-bandgap semiconductors are crucial for advancing optoelectronic devices such as photodetectors and photovoltaic cells. However, the high cost of crystalline inorganic semiconductors, along with fabrication complexities, necessitate alternative, cost-effective materials. In contrast, organic semiconductors give the advantages of tunable absorption spectra and compatibility with flexible substrates. In this work, we address the need for low-cost, high-performance narrow-bandgap materials by designing a new nonfused nonfullerene acceptor, 4T-11. This molecule features enhanced intramolecular charge transfer due to the introduction of electron-donating alkoxy substituents, leading to a significant reduced optical bandgap of 1.22 eV. The 4T-11-based organic photovoltaic device achieved an outstanding power conversion efficiency of 14.3%, the highest value for nonfullerene acceptors with an absorption onset exceeding 1000 nm. Furthermore, the 4T-11-based photodetector demonstrated exceptional responsivity, surpassing 1013 Jones across the 450–1000 nm wavelength range. This study provides valuable guidance into the molecular design of cost-effective narrow-bandgap organic semiconductors for next-generation optoelectronics.