Solution-based ultraviolet photodiode with ZnO Nanoparticle/Poly(3,4-Ethylenedioxythiophene) polystyrene sulfonate heterojunction and negative capacitance

UV detectors have attracted much attention due to their wide applications in astronomy, biology, and national defense, and their development has expanded from academia and industry to multiple fields. Over the past decade, researchers have proposed various materials and structures for the development of ultraviolet detectors, such as wide bandgap semiconductor thin film photodetectors and InGaN thin film Schottky metal insulator semiconductor photodiodes. However, the implementation of high-performance ultraviolet detectors often relies on complex and expensive manufacturing techniques such as epitaxial growth and chemical vapor deposition. Therefore, developing a simple and low-cost manufacturing process for ultraviolet detectors is particularly important.

Professor Daping Chu from the University of Cambridge and Professor Jin Li from Beihang University have collaborated to propose a simple, low-cost, and high-performance ultraviolet detector. Using ZnO NPs prepared by solution method and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), a UV sensitive heterojunction has been successfully constructed. The experiment showed that the on/off current ratio of ZnO NPs PEDOT: PSS heterojunction reached 6.7 × 10³ at 2V, and its potential barrier height was determined to be 0.64 eV.

In addition, researchers also compared and analyzed the rise time exhibited by the proposed device with other ZnO based photodetectors. The rise time generated by the method proposed in this study is 0.0745 s, which is significantly shorter than most ZnO based photodetectors. The main reason for this work is the use of ZnO NPs/PEDOT: PSS heterojunction structure. ZnO is a wide bandgap semiconductor with high electron mobility, while PEDOT: PSS is a common conductive polymer with good hole conductivity. The heterojunction interface formed between the two can effectively separate photo generated electron hole pairs. By optimizing the quality and thickness of the thin film during the preparation process, the charge transfer efficiency can be further improved, the time for charge accumulation can be reduced, and the rise time can be shortened. These results indicate that the proposed device exhibits excellent photosensitivity, and its good optical switching characteristics are suitable for fast optical addressing spatial light modulator applications.

This research successfully achieved experimental verification of a novel ultraviolet photodiode through the preparation of ZnO NPs PEDOT: PSS heterojunction based on solution technology. This device not only has the advantages of low cost and simple manufacturing, but also has the potential for large-scale production. This study systematically characterized the electrical and optical properties of ZnO NPs PEDOT: PSS heterojunction, observed for the first time the negative capacitance effect in the heterojunction, and further explored its threshold voltage and conversion frequency. The experimental results show that the rise time of the proposed ZnO nanoparticle photodiode is only 0.0745 seconds, significantly better than other ZnO based photodiodes. The trap states in ZnO nanoparticles are highly advantageous for high-resolution applications, therefore, this heterojunction exhibits enormous potential in high-resolution, high responsivity, and high-speed OASLM devices.