A flexible in-plane p–n heterojunction nano-generator with phonon-enhanced photothermoelectric effect to harvest solar energy

Abstract

Photothermoelectric (PTE) devices show a promising prospect for realizing photo-induced output voltage using infrared light, which can meet the crucial requirements for photodetectors and power supply. However, limited utilization of visible light partly weakens the ability of harvesting solar energy. Particularly, an as-prepared composite (CM) film with the unique ability to harvest solar light with a broadband spectrum from visible to infrared was presented in this study. An enlarged light harvesting range was obtained by forming an in-plane p–n heterojunction between p-type multi-walled carbon nanotubes (MWCNTs) and an n-type Ti₃C₂T_x nanosheet (MXene) film. When the interface between MWCNTs and MXene was irradiated using lasers of 405, 520, 635, 808 and 1064 nm, spontaneous separations of photogenerated electron–hole pairs originated from the photovoltaic (PV) effect (405, 520, 635 and 808 nm) and PTE effect (1064 nm). A nano-generator with ten CM films was fabricated to harvest solar energy. The PV voltage always had a fixed value as a function of incident light intensity, while the PTE voltage could be increased by adjusting the temperature difference. Finally, the peak value of the total output voltage increased to a stable value of 2.0 mV for the CM film under the irradiation of AM 1.5 G simulated sunlight. This study not only introduces the carrier separation and transmission mechanism by means of the co-action between the built-in electric field of the p–n heterojunction and thermal field, but also provides a new suggestion for better utilization of solar energy.