Emissive Charge‐Transfer States at Hybrid Inorganic/Organic Heterojunctions Enable Low Non‐Radiative Recombination and High‐Performance Photodetectors

Hybrid devices based on a heterojunction between inorganic and organic semiconductors have offered a means to combine the advantages of both classes of materials in optoelectronic devices, but, in practice, the performance of such devices has often been disappointing. Here, it is demonstrated that charge generation in hybrid inorganic–organic heterojunctions consisting of copper thiocyanate (CuSCN) and a variety of molecular acceptors (ITIC, IT‐4F, Y6, PC70BM, C70, C60) proceeds via emissive charge‐transfer (CT) states analogous to those found at all‐organic heterojunctions. Importantly, contrary to what has been observed at previous organic–inorganic heterojunctions, the dissociation of the CT‐exciton and subsequent charge separation is efficient, allowing the fabrication of planar photovoltaic devices with very low non‐radiative voltage losses (0.21 ± 0.02 V). It is shown that such low non‐radiative recombination enables the fabrication of simple and cost‐effective near‐IR (NIR) detectors with extremely low dark current (4 pA cm−2) and noise spectral density (3 fA Hz−1/2) at no external bias, leading to specific detectivities at NIR wavelengths of just under 1013 Jones, close to the performance of commercial silicon photodetectors. It is believed that this work demonstrates the possibility for hybrid heterojunctions to exploit the unique properties of both inorganic and organic semiconductors for high‐performance opto‐electronic devices. Efficient charge generation mediated by an emissive charge‐transfer state is observed in hybrid heterojunctions comprising the inorganic semiconductor copper thiocyanate and common organic semiconductors. This enables the fabrication of solar cells with very low voltage losses and highly sensitive photodetectors that can detect sub‐picowatt near‐infrared light.