Future looks bright for organic solar cells

The growing demand for energy along with its limited supply from fossil fuels, is a global concern. This has led to a tremendous increase in research in various energy disciplines.

Presently, crystalline Si (silicon) dominates the market for solar cells with an efficiency of 26%. However, due to the energy-intensive fabrication process, the panels lead to higher energy payback time. Therefore, to keep up with the growing energy demand along with comparatively lower energy payback time, organic solar cells which are flexible and easy to process are gaining popularity for a different range of applications.

With the deployment of organic light emitting diode (OLED) in televisions and phones, the future of organic solar cells appears bright. This field is interesting as organic materials and solar energy are both abundant and can be used for various direct applications. However, the commercialization of organic solar cells involves the challenge of film uniformity at a large scale so that they can be printed from roll to roll. My research work involves understanding of bulk heterojunction morphology for different polymer and small molecules, and at different processing conditions to understand its effect on the performance of the device using various structural and spectroscopic characterizations at a nanoscale level.

Organic solar cells are devices that produce electricity when photons are absorbed by the active layer, which is formed by polymers and small molecules. On mixing a p-type semiconductor (donor) with an n-type semiconductor (acceptor), a bulk heterojunction morphology is formed which opens a wide area to synthesize materials that can absorb the maximum solar spectrum. With the development of novel non-fullerene acceptors, organic solar cells have reached a maximum efficiency of 17.6% by covering a more substantial part of solar spectrum. The organic solar cell can be used for application in low power requirement devices such as flexible screen chargers, electronic clothing, and transparent window films on office buildings. One of the commercially available OSC is HeLi-on solar panel by Infinity PV which is a flexible solar panel with a battery to charge electrical gadgets.

Figure 1. Schematic of organic solar cell device along with different characterizations of active layer morphology

To increase the efficiency of organic solar cells, it is important to choose the absorber material wisely, so that it can form an optimum morphology of the bulk heterojunction for efficient charge generation, separation and collection. As the active layer of these organic solar cells are either amorphous or semi-crystalline in nature, it is imperative to study the film morphology using various microscopic techniques to improve the efficiency.

The outcome of my work about bulk heterojunction morphology can directly be helpful for chemists who design new materials to improve the efficiency of OSCs, and industries that want to process roll to roll printable solar cells. The more significant impact of the work will be to benefit the community by helping to fulfill the energy demands and making life comfortable a few years down the line. Another example of OSC application includes building integrated photovoltaic (BIPV), where solar panels can be installed on the roof, walls and even on windows and these are feasible due to transparent and flexible properties of OSCs. A prototype model HeliaSol, which are flexible solar films developed by Heliatek is already installed on the façade of a warehouse in Germany which is expected to generate 6.7 kWh electricity per year.

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavors to strengthen scientific relationships between the two countries. Graduate research scholars like me study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich their research experience.

As stated by Prof Murali Sastry, CEO of the Academy, “The Academy represents an extremely important collaboration between Australia and India. Established in 2008, it is now a strong presence in the context of India-Australia scientific collaborations. Urvashi’s work involves studying the effect of solvent additive on the morphology of a polymer and fullerene blend, and correlation of different morphology with charge separation and charge transport. It can be a step towards the commercialization of OSCs which will be very helpful to the community in future. We wish her all success.”

Research scholar: Urvashi Bothra, IITB-Monash Research Academy

Title: Micro-structural and micro-spectroscopic investigation of bulk heterojunction organic solar cells

Contact Details: urvashi.bothra@monash.edu

Supervisors: Prof. Dinesh Kabra, Prof. Christopher R. McNeill

This story was written by Mr Krishna Warrier based on inputs from the research student, his supervisors, and the IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.