The South Asian Times

19 February 2018 08:51 AM

Indian-origin researcher showcases work to create lower cost solar cells

By SATimes Team

Scientists at Stanford, including an Indian origin researcher, have shown how nanotechnology can be used to create crystalline silicon (c-Si) thin-film solar cells that are more efficient at capturing solar energy. This discovery can reduce the cost of solar energy production.

American solar manufacturers have been hit hard by cheaper imports of c-Si solar cells from their Asian counterparts. Dr. Basu Mallick, an Indian-origin researcher at Stanford University, working with her advisors Dr. Mark Brongersma and Dr. Peter Peumans, developed a new method of producing a cheaper and more efficient solar cell. She used optical modelling and electrical simulations to show that a thin-film crystalline silicon solar cell with a 2 –dimensional nanostructure generated three times as much photocurrent as an unstructured cell of the same thickness. This is because the nano-structured surface traps incoming light more effectively causing it to spend more time within the silicon material. The longer the light spends inside the solar cell – the greater its chance of getting absorbed.

This is a powerful discovery as it reveals a simple method to improve the efficiency of all silicon solar cells. One of the challenges with thin crystalline silicon solar cells is that they do not absorb the infra-red portion of the solar spectrum very well. Dr. Basu Mallick has shown nanostructuring increases the solar cell photocurrent by increasing absorption of the critical infra-red portion of the spectrum. Their work was published in the prestigious journal Optics Express and has garnered close to 200 citations including multiple book chapters.

Dr. Basu Mallick then went on to demonstrate the validity of her mathematical models of the nanostructured solar cell by actually fabricating such a device. Specifically, she patterned the active region into a square-lattice two-dimensional nanostructure. Rigorous testing including short-circuit current and quantum efficiency measurements showed this new device had enhanced optical absorption, especially at longer infrared wavelengths similar to Dr. Basu Mallick’s predictions. This work was published in Applied Physics Letters with more than 30 citations including multiple book chapters. While these studies show a proof-of-concept device to demonstrate the benefits of patterning a nanostructure into the active layer of a solar cell, the cost can be reduced further by producing these thin-film silicon devices on low-cost substrates. Additionally, effective anti-reflective coating and back reflectors could be incorporated into the design to improve its efficiency. 

The two traditional major competing technologies in solar photovoltaics are crystalline silicon (c-Si) or thin films (consisting of films of Cadmium Telluride (CdTe), Copper-Indium-Gallium-Selenide (CIGS) etc). c-Si is an attractive material for photovoltaic cells due to its natural abundance and nearly ideal optical properties. One of the reasons that c-Si has captured a lion’s share of the world market in recent times is  that the prices of c-Si have been falling over the last 10 years especially due to imports from Asia. This has created competition and has put a price pressure on solar manufacturers in the US and in other parts of the world. Discoveries like the one demonstrated by Dr. Basu Mallick pave the way for manufacturers to stay competitive in the current environment.   

Dr. Basu Mallick is a Kolkata-born Physicist, Electrical Engineer and Business Manager. She obtained a bachelor’s and master’s degrees in Physics from Presidency College, Kolkata and Purdue University, Indiana, respectively. She then achieved a PhD in Applied Physics from Stanford. Her doctoral thesis is titled “Design and fabrication of nanostructures for light manipulation in solar cells and microelectromechanical systems”. Dr. Mallick has over 10 publications in prestigious journals and conferences, and multiple patents. Following her PhD, she worked as a consultant at McKinsey & Company. Currently, she works as a data scientist and strategist at Salesforce, where she continues to pursue her passion of using mathematical models to solve real world problems.

Update: 17 Jan, 2018