Inkjet printing is a powerful and cost-effective technique for deposition of liquid inks with high accuracy, which is not only of great significance for graphic applications but also has enormous potential for the direct printing of optoelectronic devices. This review highlights a comprehensive overview of the progress that has been made in optoelectronics fabrication by the inkjet printing technique. The first part briefly covers the droplet-generation process in the nozzles of printheads and the physical properties affecting droplet formation and the profiles of the printed patterns. The second section outlines the recent activities related to applications of inkjet printing in optoelectronics fabrication including solar cells, light-emitting diodes, photodetectors and transparent electrodes. In each application field, the challenges with the inkjet printing process and the possible solutions are discussed before a few remarks. In the last section, a brief summary on the progress of inkjet printing fabrication of optoelectronics and an outlook for future research effort are presented.

The modification of zinc oxide (ZnO) with silver (Ag) has proven to be an effective strategy to enhance the optical and electrical properties, in which the interactions between ZnO and Ag are critically determined by the structure and morphology of the ZnO–Ag hybrids. In order to achieve homogeneous and controllable distribution, polydopamine (PDA) was introduced via in situpolymerization to assist the decoration of ZnO nanorods (NRs) with Ag nanoparticles (NPs). Compared with pristine ZnO NRs, the light absorption is significantly enhanced for the PDA assisted Ag-decorated ZnO, which is attributed to the Ag NPs as well as the carbonized PDA thin film. Ag NPs of small size enhance the multiple/high-angle scattering from localized plasmonic effect, which increases the light path length hence traps more light. The carbonized PDA film is further beneficial to the absorption of the visible light. The Ag-decorated ZnO NRs on fluorine-doped tin oxide (FTO) coated glasses were then used as photoanodes of the photoelectrochemical (PEC) cell. The short circuit current density (J_SC, 1.8 mA cm⁻²), maximum photo current conversion efficiency (PCE, 3.9%) and lifetime (3.07 mA cm⁻² at 500 seconds) are achieved with an optimized loading of Ag nanoparticles derived from 0.01 M silver nitrate (AgNO₃), which are found to be much higher than those of pristine ZnO NRs and other reported Ag–ZnO-based photoanodes. The overall PEC performance improvement is attributed to the localized plasmonic effect enhanced light harvesting as well as the facilitated charge transport and inhibition of recombination of electrons and holes from both Ag nanoparticles that act as an electron acceptor and carbonized PDA film as stabilizer and separator.

Fabrication of small-sized patterns of inorganic semiconductor onto flexible substrates is a major concern when manufacturing wearable devices for measuring either biometric or environmental parameters. In this study, micro-sized flexible ZnO UV photodetectors have been thoroughly prepared by a facile inkjet printing technology and followed with heat treatments. A simple ink recipe of zinc acetate precursor solution was investigated. It is found that the substrate temperature during zinc precursor ink depositing has significant effects on ZnO pattern shape, film morphology, and crystallization. The device fabricated from the additive manufacturing approach has good bendability, Ohmic contact, short response time as low as 0.3 s, and high on/off ratio of 3525. We observed the sensor’s dependence of response/decay time by the illuminating UV light intensity. The whole process is based on additive manufacturing which has many benefits such as rapid prototyping, saving material, being environmentally friendly, and being capable of creating high-resolution patterns. In addition, this method can be applied to flexible substrates, which makes the device more applicable for applications requiring flexibility such as wearable devices. The proposed all-inkjet-printing approach for a micro-sized ZnO UV photodetector would significantly simplify the fabrication process of micro-sized inorganic semiconductor-based devices. A potential application is real-time monitoring of UV light exposure to warn users about unsafe direct sunlight to implement suitable avoidance solutions.

A Cu ₂ O/ZnO nanofilm photodetector was fabricated on flexible SWNT-coated substrates, which demonstrates excellent responsiveness under UV/visible illumination without external bias.