Organic photovoltaic cells are increasingly finding use because of its key properties like flexibility, and low cost in production. Organic Photovoltaic cells are a kind of solar cell which uses polymeric materials to capture the sunlight instead of semiconductors which are used in most photovoltaic cell. The only downside with organic photovoltaic cells is the complex power conversion process which involves independent charge formation and transport process.
This serves as a big impediment in popularizing use of organic photovoltaic cells. However researchers from Japan have found out a way to steer around this problem and developed a method deduce the absolute value of charge formation efficiency. The method uses a combination of two types of spectroscopy to get over this problem.
The two types of spectroscopy which the team used to find out the charge formation efficiency was photo-
- Induced spectroscopy to determine the change in absorption after femtosecond photo-pulse excitation
- Electrochemical spectroscopy to examine the absorption change due to charge injection
Professor Yutaka Moritomo, Institute of Materials Science at the University of Tsukuba said, “By qualitative analysis of the spectral change, we can deduce how many charges are produced by one photon — its charge formation efficiency,”
It is a significant step forward and the team found out that the charge formation efficiency remained high at very low temperatures of 80K.
This is a surprising phenomenon. The Positive and the negative charges are bound in an organic photovoltaic device in the form of an exciton. An exciton is basically a bound state of an electron with a hole and is attracted towards each other by electrostatic forces. Explaining this peculiarity Moritomo explains that it was believed that charge formation cannot occur without a thermal activation process. However the research made it amply clear that the process of charge formation in any organic photovoltaic device is purely quantum mechanical and this explains the high charge formation at very low temperature.