Efficient photothermoelectric detection by layered Bi2 <b>+</b> 2 <i>n</i> O2 <b>+</b> 2 <i>n</i> Se <i>n</i> Cl2 superlattices with ultralow thermal conductivity

Abstract

Photothermoelectric (PTE) detection, consisting of photothermal and thermoelectric conversion processes, is a promising self-powered strategy for room-temperature optoelectronic sensing. However, a fundamental trade-off between electrical and thermal transport remains a challenge in realizing an efficient PTE effect. Herein, the theoretical calculations, based on the modified two-temperature model and thermal diffusion equation, verify that extremely low thermal conductivity along both in-plane and out-of-plane, as well as a suitable carrier concentration, can achieve excellent PTE performance. In the experiment, furthermore, as a concept-proof, layered Bi–O–Se–Cl superlattice crystals (such as Bi4O4SeCl2 and Bi6O6Se2Cl2) provide an ideal platform to prove our theory because they have the same order thermal conductivity (0.1 W m−1K−1) as that of air (0.03 W m−1K−1). Spectacularly, the Bi6O6Se2Cl2 device demonstrates excellent optoelectronic detectivity at the infrared regime (a responsivity of 87.29 mV W−1 at 1550 nm, a noise-equivalent power of 10.63 nW Hz−1/2, a detectivity of 5.64 × 106 Jones, and a response time of 88 ms). This superior performance comes from optimized synergetic manipulations of extremely low thermal conductivity (in- and out-of-plane thermal conductivity are 0.62 and 0.2 W m−1K−1, respectively) and suitable carrier concentration (∼1020 cm−3), in line with theoretical prediction. This work not only proposes the criteria of material parameters to have an ideal PTE effect but also establishes Bi2 + 2nO2 + 2nSenCl2 superlattices as a promising self-powered broadband photodetector.