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With the development of wearable electronic technology, the flexible photodetectors have attracted widespread attention, and it is of great significance to develop flexible, eco‐friendly and low‐cost photodetectors. Cellulose paper, as a flexible, eco‐friendly, low‐cost, lightweight, customizable, biodegradable and renewable material, has received enthusiastic attention and rapid development in the field of photodetectors in recent years. In this review, it is focused on the research progress of paper‐based (PB) photodetectors. First, the fabrication methods of PB photodetectors are discussed, including electrode materials and optoelectronic functional materials. Then, this review systematically summarizes and analyzes the achievements of PB photodetectors on photoelectric performances (spectral response range, responsivity, detectivity, response/recovery times and on/off ratio) and flexibility characteristics (bending angle and bending cycle). In terms of key performance indicators, the PB photodetectors reported so far can detect multiple wavelengths of light from UV to near‐infrared with the maximum detectivity of 1013 Jones. In addition, the various applications of PB photodetectors is reviewed and discussed. Finally, it is look forward to the future development of PB photodetectors in terms of fabrication methods, photoelectric and flexible performances, and applications. With this review, it is hope that it will promoted the future development of PB photodetectors. [ABSTRACT FROM AUTHOR]

A photodetector (PD) with high performance and stability in a broad range of wavelengths is essential for the broadband application in sensing, communication, and imaging. The heterojunction PDs based on CuInS2 (CIS) nanoflakes (NFs) and TiO2 nanorod arrays (NRs) were fabricated by a solvothermal method, and demonstrated a wide spectral response range from ultraviolet (UV) to visible without external bias. The enhanced responsivity (R), detectivity (D*), light sensitivity, linear dynamic range (LDR) and response time for the self-powered CIS/TiO2 PD is 44.8 mA W−1, 1.3 × 1012 Jones, 2.7 × 104, 88.5 dB and 2 ms by regulating the growth process of CIS NFs in the precursor solution. The excellent dual-band detection ability in the UV and visible light demonstrates the practical application feasibility and practicability of the self-powered PD in the "OR" gate of light-controlled digital logic circuit and encrypted VLC applications. [ABSTRACT FROM AUTHOR]

Reducing carrier trapping in the grain boundary of semiconductor materials can improve the carrier transport. Adding Na2EDTA in the electrolyte can regulate the growth process of Cu2O thin films electrochemically deposited at low temperature, improve the crystal quality, and transform from the polycrystalline structure into a single-crystal-like structure oriented along the (111) crystal plane. As a result, the interface transfer resistance of ZnO/Cu2O heterostructure devices is reduced, the photogenerated carrier transport ability is improved, and the self-powered photoresponse properties of heterostructure devices are improved. Based on the dual-band photoresponse characteristics of ZnO/Cu2O, a device without bias voltage was applied in the "OR" gate of a UV and visible dual-band light controlling digital logic circuit. The encrypted optical signal was realized and the security of visible light communication was improved by the encoded UV and visible dual-band light. [ABSTRACT FROM AUTHOR]

The tunable bipolar binary photoresponse characteristics (positive and negative current value changes) of heterojunction photodetectors (PDs) are used to realize the applications of optical communications, optical information storage, and multiple logic circuit operations of light. ZnO/Cu2O heterojunction PDs with photovoltaic effects show a fast and broad-spectrum photoresponse to UV and visible light. A high light switching on/off ratio of 2.7 × 105, a responsivity of 0.55 A W−1 and a detectivity of 1.5 × 1013 Jones were obtained under 470 nm illumination without applied bias. The PDs exhibit controllable bipolar binary photoresponse characteristics by adjusting the competitive relationship between the photo-generated current and the internal junction current for the PDs under different light (intensity or wavelength) and small applied bias voltage (0 < Vbias < Voc). The PDs exhibit a binary photoresponse in a wide spectrum from UV to visible light. The binary photoresponse states used as "1" and "−1" digital codes can achieve programmable processing of digital signals. The results provide a universal example to realize the bipolar binary photoresponse by regulating the light wavelength, light intensity and applied external bias for the heterojunction PDs with the photovoltaic effect. [ABSTRACT FROM AUTHOR]

The morphology and geometry of semiconductors will affect the photoresponse performance of mixed-dimensional heterojunction photodetectors (PDs). Self-powered UV PDs based on mixed-dimensional heterostructure arrays are formed from two-dimensional NiO nanosheet arrays and one-dimensional TiO2 nanorod arrays. The Fermi level position and carrier concentration of the NiO nanosheets can be adjusted by the thickness of each layer and film. The enhanced built-in potential field of the NiO/TiO2 interface decreases the charge transfer resistance and the appreciated carrier transfer path improves the photogenerated carrier separation and transfer ability without external bias. The self-powered NiO/TiO2 heterojunction device demonstrates a large responsivity of 0.86 A W−1, a high detection sensitivity of 1.6 × 1013 Jones and a fast photoresponse time of 3 ms under weak UV light illumination. [ABSTRACT FROM AUTHOR]

The initial reactant concentration and the substrate play an important role on the nucleation and growth of MoS2 nanostructures during hydrothermal growth. In this work, MoS2 nanoflakes are grown on FTO and TiO2 nanorod arrays (NRs) substrates. The morphology, optical and photoelectric properties of MoS2 nanoflakes are affected by the initial reactant concentration. Compared with the FTO substrate, MoS2 nanoflakes tend to grow on TiO2 NRs substrates due to less mismatch between TiO2 and MoS2. The large surface roughness and the presence of surface states of the TiO2 NRs facilitate the nucleation and growth of MoS2 nanoflakes. The photoelectric characteristics of MoS2/TiO2 NRs compositions have been investigated. The MoS2/TiO2 NRs compositions prepared using the initial reactant concentration with 4 mM S atom concentration exhibit the higher photoresponse behavior, which is attributed to the better heterojunction contact interface between MoS2 nanoflakes and TiO2 NRs. MoS2 nanoflakes can not completely cover the TiO2 NRs under low initial reactant concentration, resulting in the small area of the contact interface. On the other hand, MoS2 nanoflakes tend to form the self-assembly nanoflowers under high initial reactant concentration, which induces the carriers recombination in MoS2, the poor transport properties of MoS2 and the detrimental effects on the photogenerated current. [ABSTRACT FROM AUTHOR]

Binary photoresponse characteristics can help realize optical signal processing and logic operations. UV photodetectors (PDs) with SnS x nanoflakes and TiO 2 nanorod arrays (NRs) show a novel binary photoswitching behavior (change in current from positive to negative) by manipulating the light wavelength without an external power source, utilizing the interfacial recombination of the photogenerated carriers in the type-I SnS x /TiO 2 heterojunctions. The enhanced responsivity ( R* ), detectivity ( D * ), and fast photoresponse time for self-powered SnS x /TiO 2 PDs can be achieved by adjusting the phase ratio of SnS and SnS 2 nanoflakes. The binary photoswitching in the self-powered UV PDs can be applied in the encrypted optical signal processing and imaging in some special conditions without external bias.