Optoelectronic devices based on liquid-semiconductor heterojunctions

Optoelectronics is a critical field that merges optics and electronics to develop devices capable of converting electrical signals into light and vice versa. This area allows for a variety of applications, including renewable energy, communications, and medical imaging. Semiconductors are essential to the operation of optoelectronic devices like LEDs, photovoltaic cells, and photodetectors because of their special properties in controlling electrical current and interaction with light. With the ongoing advancements in technology, there is a growing demand to introduce new heterojunctions, such as liquid-solid (LS) heterojunctions, to enhance device performance and efficiency. These new heterojunctions present prospects for enhanced charge transfer, flexible processing, and novel functionality in optoelectronic applications. This thesis explores the fundamental properties and applications of LS interfaces in optoelectronics. The work provides insights into the charge transfer mechanisms, and the structured order of water molecules at interfaces. It also highlights the potential of LS interfaces in developing high-performance electronic and optoelectronic devices, such as triboelectric nanogenerators (TENGs) and photodetectors, that exploit unique interface dynamics for energy harvesting and sensing. One of the most important discoveries is the memory-like behaviour of the triboelectric response between ionic liquid and 2D MoS2 under light illumination, which is described through electronic band diagrams, equivalent electrical circuits, contact angle measurements, and electric double layer. This behavior is harnessed to demonstrate synaptic features, such as potentiation, inhibition, and short-term to long-term memory conversion. Additionally, the work introduces the pyroelectric effect of interfacial water for the first time. Moreover, high-performance, broadband, and polarization-sensitive pyroelectric-photoelectric photodetectors based on 2D MoS2-water and silicon-water heterojunctions are demonstrated. These photodetectors show fast response times which makes them suitable for high-frequency applications. Finally, the thesis proposes future research directions, including the application of the findings to enhance biosensing technologies and microfluidics. The memory-like behavior observed through tribo-phototronic effects could lead to the development of highly sensitive and selective biosensors for detecting a wide range of biomolecules. Integrating LS interface properties into microfluidic systems could improve fluid control and analysis, with applications in on-chip water purification, selective ion separation, and precise fluid handling. Overall, this thesis contributes to our understanding of LS interfaces and the promise they have in optoelectronics.