Dual-polarity response photodetectors (PDs) take full advantage of the directivity of the photocurrent to identify optical information. The dual-polarity signal ratio, a key parameter that represents the equilibrium degree of responses to different lights, is proposed for the first time. The synchronous enhancement of dual-polarity photocurrents and the amelioration of the dual-polarity signal ratio are beneficial to the practical applications. Herein, based on the selective light absorption and energy band structure design, a self-powered CdS/PEDOT:PSS/Au heterojunction PD consisting of a p-n junction and a Schottky junction exhibits unique wavelength-dependent dual-polarity response, where the photocurrent is negative and positive in the short and long wavelength regions, respectively. More importantly, the pyro-phototronic effect inside the CdS layer significantly improves the dual-polarity photocurrents with the maximum enhancement factors of 120%, 343%, 1167%, 1577%, and 1896% at 405, 450, 532, 650, and 808 nm, respectively. Furthermore, the dual-polarity signal ratio tends to 1:1 due to different degrees of the enhancement. This work provides a novel design strategy for dual-polarity response PDs with a simple working principle and improved performance, which can supply a substitution for two traditional PDs in the filterless visible light communication (VLC) system.
Keywords: CdS; dual-polarity response; dual-polarity signal ratio; filterless visible light communication; pyro-phototronic; selective light absorption.
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