High-Performance Photodetectors with an Ultrahigh Photoswitching Ratio and a Very Fast Response Speed in Self-Powered Cu₂ZnSnS₄/CdS PN Heterojunctions

Abstract

Cu 2 ZnSnS 4 (CZTS) has been extended to the field of photodetection owing to its outstanding optoelectronic properties. However, the existence of the ineluctable defects in CZTS semiconductors affects and even determines the optoelectric processes including carrier generation, relaxation, transfer, and recombination. Moreover, photoresponse correlated to the defects in CZTS photodetectors has not well been documented and the possible physics mechanism is still unexplored. High-performance and self-powered PN heterojunction photodetectors are built from Cu 2 ZnSnS 4 and CdS films. The devices exhibit a steady rectifying behavior and a prominent photovoltaic effect. The peak values of responsivity and detectivity are 220 mA W −1 and 2.69 × 10 10 Jones, respectively. A very fast response speed with rising and decay times of up to 18 and 19 μs and an ultrahigh photoswitching ratio beyond 10 4 are demonstrated in these photodetectors. An abnormal dependence of the light response parameters on the incident power and temperature is found in these devices. This anomaly is explained by the formation of the defects and/or defect dipoles, which are evidenced by the temperature dependence of the photocurrent, the dependence of the capacitance on the bias voltage at different temperatures, and the derivative of capacitance with temperature. KEYWORDS: photodetectors, Cu 2 ZnSnS 4 /CdS heterojunctions, self-powered properties, abnormal photoresponse, dependence of capacitance on the bias voltage

Enhanced Broadband Photoresponsivity of the CZTS/WSe2 Heterojunction by Gate Voltage

“…This observation at the low yield generation region for the CZTS/WSe 2 heterostructure is different from traditional photodetectors. It seems that the origin of this dissimilarity is because of the creation of trap states in the CZTS structure (which is caused by defects and/or impurities in CZTS), as reported in previous research. − Figure d–f demonstrates the energy band structure of the CZTS/WSe 2 heterostructure with trap states (denoted by T 1 and T 2 ). Without trap states, charge carriers can only be excited from the VB to the CB.…”

“…When the incident light power is lower than 30 W/cm 2 , the α value is ∼0.87 (high yield generation region) and for light powers more than 30 W/cm 2 decreases to ∼0.71 (low yield generation region). This decrease in the α coefficient (from the ideal value of 1) indicates that all incident photons cannot generate free electrons and holes in the CZTS/WSe 2 heterostructure, originating from trap states and the recombination process that plays a crucial role in charge carrier generation and recombination. , The photoresponsivity ( R ) is a critical feature of photodetectors, implying the sensitivity of a structure to irradiation power, and described as the ratio of the photocurrent generated to the irradiated light power and can be computed as follows: R = ( I − I d ) / P in …”

Van der Waals Heterostructures With Built‐In Mie Resonances For Polarization‐Sensitive Photodetection

“…Generally, R decreases as a function of P laser , and some fluctuations arise from the formation of defects and charged impurities and the recombination processes of electron–hole pairs. [ 45–47 ] For the Photodetector No.1 with bottom patterns, R can reach 10.0 A W −1 , comparable to the best performance of conventional WSe 2 /ReS 2 heterostructures. [ 13 ] For the Photodetector No.2, the maximum R of unpatterned and patterned heterojunction is 0.29 and 0.13 A W −1 , respectively.…”

Carrier recombination suppression and transport enhancement enable high‐performance self‐powered broadband Sb2Se3 photodetectors

“…In addition, the I light /I dark switching ratio can increase up to 4.13 Â 10 6 (at 10.64 mW cm -2 ), representing one of the highest values for Sb 2 Se 3 -based photodetectors. Such an interesting index is also higher or comparable to the index associated with some most advanced self-powered photodetectors, for example, Cu 2 ZnSnS 4 /CdS (I light /I dark ratio of $10 4 ), 41 CsBi 3 I 10 /SnO 2 (I light /I dark ratio of 2.33 Â 10 5 ), 1 GaN/ZnO (I light /I dark ratio of 7.36 Â 10 6 ), 42 PbS CQD/ZnO (I light /I dark ratio $10 6 ). 33 Moreover, to validate its broadband capability, the S2A3 photodetector was also examined with a 905 nm laser with light intensity ranging from 0.11 μW cm -2 to 10.64 mW cm -2 (Figure S6).…”

“…The device long‐term durability is also verified by comparing the photoresponse performance of the freshly fabricated photodetector and the same device that stored at ambient conditions for 2 months (Figure S10). Finally, the key parameters of our photodetectors are summarized in Table 1, as well as a comparison to the literature reported Sb 2 Se 3 ‐based self‐powered photodetectors, and the representative Cu 2 ZnSnS 4 , PbS, perovskite, and graphene‐based photodetectors 1,29,30,33,35,41,44–48 . The best‐performing Sb 2 Se 3 /CdS (Al) photodetector with light absorber layer growth promotion and heterojunction interface modification can achieve simultaneous high responsivity, high detectivity, high “ON/OFF” switching ratio, and ultra‐fast response.…”