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Physics behind Perovskite

Researchers at IIT Bombay have identified some unique features common to all perovskite solar cells that would lead to better understanding in terms of device physics and control parameters.

Among the renewable sources of energy, sun is probably the most promising source to meet our future energy requirements. The first Photovoltaic cell was built around 60 years ago, in 1954 at Bell Laboratories. Since then a great deal of research has been directed towards improving efficiency and reducing costs. Nevertheless, solar cells have not yet gained the popularity and acceptance as expected. The major factor that has hindered widespread acceptance of Solar cells is their high manufacturing cost.

Most of the solar panels available in the market today, are based on Crystalline Silicon technology, which is very expensive. Hence to reduce costs, along with process optimization and modifications, cheaper substitutes are also being tried and tested. One such material called perovskite, was first used in solar cells in 2009. Recently there has been widespread research on novel solar cells with perovskites as the active material for enhanced efficiency. Numerous publications about perovskite based photovoltaic cells have recently appeared in top-notch journals with efficiencies approaching 20%. Although these results were promising, there still was a lack of a unifying theoretical framework which would allow scientists at different laboratories  to compare results and design better experiments. Thus,  Professor Pradeep Nair from Electrical Engineering Department, IIT Bombay, along with his colleagues, co researchers and students, decided to try and come up with a theoretical framework to explore the fundamental device physics of  Perovskite based cells.

The research started with formulation of theoretical equations to predict the current characteristics in absence of light. The corresponding theoretical predictions (done by Mr. Sumanshu Agarwal, Graduate student, Dept of Energy Science and Engineering, IIT Bombay) were then juxtaposed with actual experimental data from labs at IITB as well as data available from existing literature, published by other researchers Oxford university, Swiss Federal Institute of Technology, Lausanne and IISER-TVM . It was observed that irrespective of the differences in materials used and in the fabrication methodology employed, the Perovskite based Solar cell exhibited two distinct parameters, namely the ‘ideality factor’ and the ‘Voltage exponent’ at high bias regions, that remained roughly the same throughout. With this knowledge of the device characteristics, they came up with a theoretical framework for the working of the cells consistent with their findings, which was published in the prestigious Journal of Physical Chemistry in November 2014.

After the path breaking research on the Dark current characteristics, Prof.Nair and the team are now focussed on exploring the illuminated current-voltage characteristics. With the Dark IV characteristics well understood, their aim is to understand and analyze system level performances and to build a framework to predict how perovskite solar cells would perform under variable illumination conditions.

(Published in Journal of Physical Chemistry Letters, November 12 , 2014)

The above mentioned research on perovskite solar cells was conducted at IIT Bombay using the facilities available at the Center of Excellence in Nanoelectronics (CEN) and National Center for Photovoltaic Research and Education (NCPRE). This research is partially supported by the Solar Energy Research Institute for India and the United States (SERIIUS).

Write-up prepared by (based on inputs from the researchers)  : Dhruv Nigam, P.Pradeep

Graphics by : Sagar Sant


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