Organic photovoltaic cells are now one step closer to become the future of energy conversion. Scientists at the Japan’s University of Tsukuba have developed a method to measure efficiency in organic cells and screen materials. Organic photovoltaic cells are simply a type of solar cells that use polymeric materials to capture sunlight. They have shown huge promise as energy conversion devices, mainly due to their low-cost production and flexibility.

Organic Photovoltaic Cells

Use spectroscopy to screen materials for organic photovoltaic cells

But one challenge holding back this technology was the complexity of their power conversion process, according to a study published in the journal Applied Physics Letters. The conversion process involves separate charges formation and transportation pathways. Scientists in Japan have found that spectroscopy could be a way to identify materials for organic photovoltaic cells by studying their charge formation efficiency.

They used a combination of two types of spectroscopy to determine the absolute value of the charge formation efficiency. They first used photo-induced spectroscopy to measure the change in absorption after femtosecond excitation. And then they determined absorption change due to the charge injection using electrochemical spectroscopy.

Charge formation in organic photovoltaic devices is purely quantum mechanical

Professor Yutaka Moritomo, lead author of the study, said they deduced the number of charges produced by one photon using qualitative analysis of the spectral change. The charge produced by a photon is called charge formation efficiency. Scientists found that the charge formation efficiency remained high (0.55) even at lower temperatures. It’s a giant leap forward, said Moritomo.

In an organic photovoltaic device, the positive and negative charges are strongly bound as an exciton. Therefore, the charge formation was expected to be extremely difficult without any thermal activation process. But this study proved that, in organic photovoltaic devices, the charge formation process is completely quantum mechanical.

Moritomo said his team’s method could be used to quickly screen the materials for organic photovoltaic cells by charge formation efficiency. Now they are studying the mechanism of charge formation.