From solar energy to electricity

 

Solar power is arguably the cleanest, most reliable form of renewable energy available, and it can be used in several forms to help power homes or businesses. In the last decades organic solar cells (OSCs) have been considered as a promising photovoltaic technology with the potential to provide reasonable power conversion efficiencies combined with low cost and easy processability. Unexpectedly, perovskite solar cells (PSCs) have experienced unprecedented rise in power conversion efficiency thus emerging as a highly efficient photovoltaic technology. OSCs and PSCs are two different kind of devices with distinct charge generation mechanism, however share some similarities in material processing, thus standard strategies developed for OSCs are currently being employed in PSCs. Here in Baran’s OMEGA Lab we develop photovoltaic materials and devices to achieve higher performance and reliability at lower cost and to enhance understanding of the chemistry behind the material growth and the physics behind the device operation. We also aim to understand the stability and degradation processes that occur in the solar cells.

 

 
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Organic Photovoltaics

Organic semiconductors are envisioned to positively impact human life through applications ranging from sensors and displays to lighting and photovoltaics. As opposed to most of their inorganic counterparts, organic devices can be printed from solution on plastic substrates, allowing for extremely thin, lightweight and conformable products that can be manufactured over large areas with freedom of shape. In the last decade, organic photovoltaics (OPVs), leveraging the impressive improvement in device efficiency and stability, have gradually moved from a lab curiosity to a niche market. The OPV landscape is nowadays facing a new era, ferried by the development of novel and stable acceptor materials, the so called non fullerene acceptors (NFAs), making the 15% power conversion efficiency (PCE) threshold not anymore a research dream but a real goal. Here in OMEGA Lab we focus on further device optimization and characterization of NFA-based solar cells, such as solvent additive,  interfacial material, and ternary blend strategy. 

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Photovoltaic Stability and Degradation

In the last few years, higher power conversion efficiencies of organic and perovskite solar cells has attracted the attention of the research community and industry. However, the life time of the devices is a serious setback to their commercialization. Here, in OMEGA Lab, these issues are being addressed through understanding the degradation mechanisms of these high efficiency solar cells.  

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Perovskite Photovoltaics

Perovskite-based photovoltaics are among the most recent solar energy technologies to emerge from the scientific community. Since 2009, perovskite solar cell efficiency has risen from 3.8% to 23.3% in 2018 amongst intense interest from many research groups globally. Perovskite photovoltaics show great promise for the future given their use of low-cost, earth-abundant materials and simple processing techniques. In addition, the electrical and optical properties of perovskites can be finely tuned by changing the material’s chemistry, allowing their use in applications such as tandem photovoltaics and photodetectors. In OMEGA lab, we investigate the interfaces between different layers in perovskite solar cells in order to improve device efficiency and stability .

Printing, the world of endless possibilities for the future

 

Printing technologies are emerging in the field of photovoltaics, as they are compatible with solution processable materials. Printing offers endless possibilities in terms of customization, freedom of design, ability to use flexible substrates for large-scale processes. Our research focuses on the optimization of the printing processes to develop low-cost and highly efficient solar cells by using high throughput techniques, such as inkjet printing, 3-D printing and slot-die coating. In addition, our approach includes the use of eco-friendly solvents for the next generation of green solar cells.

 

 
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Inkjet Printed Organic Electronics

Digital printing is evolving from being used to graphically display information into a tool that generates and enhances a variety of functionalities. The phrase “Printing beyond color” is taking a new meaning when adding electronic functions to paper and plastics through the use of organic materials, with the advantage of properties such as flexibility, stretchability, and freeform deposition.  In OMEGA Lab, we are bridging the gap between research-scale device fabrication and consumer-ready manufacturing. Our work focuses on the engineering of inks that allow a repeatable printing process, the optimization of printing parameters to yield high-efficiency functional films, and the study of interfaces between the different layers that encompass fully working devices.  Through our research, we aim to produce fully-printed devices including solar cells, thermoelectric generators, capacitors, and a variety of sensors to enable a wide range of applications in packaging, healthcare, construction, and disposable/single-use electronics. 

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3D Printed Organic Electronics

Three-dimensional (3D) printing has emerged as a promising fabrication process used in a wide variety of fields including aerospace, medicine, architecture, education, and automotive due to its versatility, customization, and its ability to produce prototypes in a speedy manner. While still a young technology, there has been increased interest to extend the advantages of additive manufacturing by adding functionalities in the 3rd dimension in the form of electronic devices as well as the change of form or function over time through stimuli such as heat, current or light. Our lab focuses on the formulation of materials (both organic and inorganic) that go beyond creating conductive paths but rather add extended functionality to fabricate electrical components for energy harvesting, energy storage, sensing and actuating in 3 dimensions. Additionally the design of customized parts with complex shapes and sizes in combination with material properties such as flexibility, elasticity, will permit the development of functional devices that can be used for smart objects, soft robotics, and medical applications. 

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Slot-Die Coating

Slot-die coating is one of many methods that can be used to deposit a thin liquid film to the surface of a substrate. Compared to other existing coating techniques this method can easily integrated from lab to scale-up processes. The process results with best quality uniform thin film deposition across the length/width of the coating surface. This coating technique is favorable with a wide range of solution of different viscosities.  The process is also suitable with roll-to-roll deposition, this method is of great interest among researchers these days for transition from lab-scale to pilot-level production. Currently, the main focus of research is to use slot-die coating technique in the field of photovoltaic, OLEDs, quantum dots and many others. 

Waste heat to Electricity

Thermoelectric devices have recently raised interest as a compelling solution for electricity generation by harvesting heat dissipated from heating systems, automotive engines, power plants, solar farms, and smartphone devices. In thermoelectric generators (TEGs), p- and n-type thermoelectric materials are sandwiched between two metallic junctions. When a temperature gradient is applied between the two junctions, charge carriers diffuse from the hot to the cold junction, thereby generating electrical current and voltage. In our OMEGA lab, we are developing p- and n-type organic and hybrid organic/inorganic thermoelectric materials that are compatible with low-cost scalable processes such as printing and coating methods. We aim to realize high performance and low-temperature processed thermoelectric organic and perovskite materials by comprehensively understanding the material characteristics and materials design.

Thermoelectric Generators

Organic Thermoelectrics

Development of efficient and versatile organic thermoelectrics using organic semiconducting/conducting materials with novel functionality, such as extremely deformable/stretchable and self-healable/recyclable polymers and small molecules. Based on these materials, we are demonstrating wearable and skin-attachable thermoelectric devices via high-throughput printing techniques including doctor-blade, ink-jet and 3D printing.

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Perovskite Thermoelectrics

The versatile nature of hybrid halide perovskites have already resulted in a multitude of applications apart from photovoltaics. The ultralow thermal conductivity and high seebeck coefficient of these hybrids makes them suitable candidate for future thermoelectrics. Our focus in this project is to explore the thermal transport properties of these hybrids for efficient thermal management and device applications. 

Stability Studies

Material Properties

In order for thermoelectric materials to be readily available in the market, there are several challenges to overcome. In the OMEGA Lab we are focusing on understanding the electronic and mechanical properties of thermoelectric materials in order to improve performance and process-ability for large area applications. In addition we are exploring the effects of doping as well as the use of different systems to improve the stability of the materials under different stress conditions. Lastly, we aim to make the materials suitable for deposition with high throughput techniques such as inkjet or 3D printing.