Advanced Printed Semiconductors for Energy and Optoelectronics

Our research includes smart and advanced materials for the emerging printed optoelectronics, with the center focus on development of the photovoltaic and photodetector technologies. Ultrathin, lightweight, robust and economical to manufacture: these key features distinguish printed electronics from traditional semiconductor technologies. Our research encompasses all key aspects of developing optoelectronic devices, including fundamental issues, performance, and stability by using experimental and theoretical methods. The key themes of our research are:

• Organic Photovoltaics

An important milestone towards organic photovoltaics (OPVs) commercialization has been surpassed by reaching the power conversion efficiencies (PCE) of over 18%. To overcome the absorption and thickness limitations, the concept of ternary near IR sensitization of organic solar cells has been explored in the last decade. As one of the pioneer research groups in the development of “Ternary Organic Solar Cells”, we demonstrated the potentiality of this concept and comprehensively investigated various prototype organic ternary systems with a central focus on the fundamental complexity of microstructure and charge transport mechanisms. Ternary/multicomponent solar cells are nowadays a leading strategy in organic photovoltaic technology with the potential to further address the challenges of global energy demand and climate emergency. Currently, we work on the stabilization of organic solar cells upon various strategies. We investigate the impact of our approaches on the thermal- and photo(chemical)-stability of the derived solar cells.

However, wide variety of the solution-processed organic optoelectronics, e.g. photovoltaics, photodetectors and light emitting diodes, are processed from chlorinated organic solvents. Therefore, their printing in large area at ambient conditions can potentially impact the human health and environment. The use of aqueous / alcohol-based nanoparticulate dispersions in printable optoelectronics offers a promising approach to control the donor: acceptor morphology on the nanoscale with the benefit of environmentally-friendly, solution-based fabrication. The final nanostructure of the composite nanoparticles (NPs) is governed by the competition between thermodynamics and kinetics during the particle formation. A fine tuning and control of these variables require prior observations and in-situ measurements. Therefore, we work on the in-situ analysis of the size growth and morphology evolution of the organic colloidal composite NPs by employing a stopped-flow apparatus equipped with various optical spectroscopic and structural characterization methods. In addition to the fundamental investigation of NPs nanomorphology formation, we study the mesoscale microstructure of NP-incorporated films, and their transport dynamics for application in organic electronic devices.

• Perovskite Photovoltaics: 

Organic- inorganic hybrid perovskite photovoltaics (PPVs) have attracted tremendous attention due to rapid progress in terms of PCE in the last few years, from 3.8% to present record values in excess of 25%. However, fundamental problems, such as the toxicity of hybrid lead halide perovskites, hysteresis and structural instability remain to be solved for perovskite solar cells. Indeed, the low-temperature solution-processing of perovskite films inevitably causes formation of a certain amount of defects on the surface and at the grain boundaries, which lead to serious trapping, charge accumulation, and recombination problems as well as stability issue. To address these key issues, we pursue the interface engineering and defects passivation within a comprehensive experimental study on various concepts supported by theoretical calculations.

Furthermore, the natural moisture resistance of 2D perovskites attracted the community’s attention to their potential as photoactive layer or even interfacial materials deposited on top of 3D perovskites. How to control the crystal orientation and the poor charge transport property of the most used organic spacer cations to form the 2D perovskite layers are hindering issues for their application and commercial-scale production. To develop highly efficient and stable 2D perovskite solar cells, therefore, we work on the design of novel organic cations with an outstanding hydrophobic nature and charge transport ability and also on the development of promising approaches to control the crystal growth orientation.

• Hybrid Organic-Inorganic Detectors:

A large number of optoelectronic technologies which still rely on inorganic semiconductors face substantial limits to be printed in large area on flexible substrates through solution-processed methods. Hybrid systems, a combination of the unique properties of both organic and inorganic semiconductors, are of significant interest to develop printed hybrid electronic devices for use in modern applications. We focus particularly on the comprehensive understanding, design, and development of printable hybrid devices by implementing an appropriate inorganic or hybrid compound in the form of nano-micro structures into the organic host matrices. Photodetectors, IR detectors, and X-ray detectors are a few examples of the optoelectronic devices which would benefit from the outcome of our research immensely.

These broad and comprehensive studies allow us to address several key fundamental issues in the field of printed optoelectronics and develop highly efficient and stable photovoltaic / detector devices.