If you’re familiar with solar energy and the methods of converting the energy from the sun to electrical energy, you will know that one drawback to this method is the low efficiency. For many years, the efficiency of these solar cells was between 14% and 18% and it recently peaked at 25%; heralding a new wave of advancement.
Organic Solar Cells
But the emergence of organic solar cells made all the difference in this area. These organic solar cells are made from carbon-based materials and the potentials they offer are truly radical. The technology for printing is efficient and low-cost, as well as the colors available for use. These organic solar cells can be built to be semi-transparent and they have a variety of colors you can choose from. This feature makes it easy to integrate them into any kind of building without compromising the aesthetics of the building.
Another advantage of these organic solar cells is the fact that they are flexible. These solar cells have almost negligible weight and this means that they can power the sensors to be used for the internet of things applications. This is yet another area of technology that promises to change the scope of solar energy conversion and electrical engineering as a whole.
The Issue with Organic Solar Cells
As exciting as the technology is, it is not without drawbacks. One major issue with solar organic cells is the energy losses associated with them. These energy losses can become really significant for large applications and it is important that they are curtailed if solar organic cells are going to achieve any form of widespread acceptance.
It has also been observed that the open-circuit voltage of solar cells is normally lower than the values that we get in an inorganic or perovskite photovoltaic device, even though the bandgaps are comparable. This means that the energy loss during the charge separation registers as the chief cause of voltage loss.
So now, how do we work it? How can it be done? What is expected? What is the best we can get?
New Design Rules Governing Organic Solar Cells
To answer this question, researchers at the Department of Biomolecular and Organic Electronics at Linkoping University decided to formulate some design rules to improve the power conversion and also mitigate the energy loss. This research, led by Feng Gao, an associate professor in the same division, challenges a number of established ideas pertaining to the design of organic materials.
With these rules, the research team already presented instances of low energy losses as well as enhanced power conversion. And these design rules are also very promising. As earlier stated, recent laboratory experiments carried out on silicon wafers is about 25% but the theoretical limit for energy efficiency with organic solar cells is 33%.
How Does It Work?
Photoelectricity, which is the governing principle by which electrical energy is produced from the sun, involves the excitation of photons in the solar cell. This excitation then causes electrons to become mobile and then holes are formed.
For these bound electrons to be separated, there is an acceptor material that is added and this results in the loss of yet, more energy. For two decades now, this issue has been prevalent and it has been a cause for concern.
The researchers concluded on the two ways by which the issue could be mitigated via a combination of spectroscopic and quantum-chemistry approaches. They then presented two fundamental rules;
- Reducing the energy offset between the donor and the acceptor.
- Ensuring that the low-gap component in the mix consists of a high level of yield even with light from non-thermal sources.
A new donor-acceptor system was formulated and this was a combination of efficient photocurrent generation and electroluminescence yield, totaling about 0.03%. The non-radiative voltage losses were as small as 0.21V. The rationale that further explains how the performance of high open-circuit voltage solar cells can be enhanced is also presented.
This research was carried out by 25 different researchers from seven research institutes in countries spanning the United States of America, China, and Europe. The resource for the grant was also provided by sources in Europe, the United States, and China.
For this work, they pored through several various works on the subject matter and some existing beliefs were discarded in the process. One thing we can all agree on is the fact that these design rules have had significant success in the prior demonstration. The results being achieved now, although incompatible with the earlier belief, is underpinned by experimental results.