Photothermal and Joule-Heating-Induced Negative-Photoconductivity-Based Ultraresponsive and Near-Zero-Biased Copper Selenide Photodetectors

The development of a highly responsive, near-zero-biased broadband photo and thermal detector is required for self-powered night vision security, imaging, remote sensing, and space applications. Photothermal-effect-based photodetectors operate on the principle of photothermal heating and can sense radiation from the UV to IR spectral region for broadband photo and thermal detection. This type of photodetector is highly desirable, but few materials have been shown to meet the stringent requirements including broadband optical/thermal absorption with high absorption coefficients, low thermal conductivity, and a large Seebeck coefficient. Here, we demonstrate ultraresponsive, near-zero-biased photodetectors made of mass-producible Cu2±xSe nanomaterials. Our photodetectors are fabricated with powder pressing and operate on the principle of negative photoconductivity that utilizes the Seebeck effect under the combined effects of Joule and photothermal heating to detect extremely low levels of broadband optical radiation. We show that copper-deficient Cu1.8Se and selenium-deficient Cu2.5Se copper selenide materials have negative photoconductivity. However, stochiometric Cu2Se copper selenide shows positive photoconductivity. We demonstrate that a photodetector made from the Ag:n+-Cu1.8Se:p-Ag:n+ system has the best photoresponse and generates a 520 mA/mm negative photocurrent and a high responsivity of 621 A/W under low bias.