26 November 2021

A small guest molecule in the right place makes it possible to produce energy-efficient organic solar cells using eco-friendly solvents. A record efficiency over 17% is demonstrated. In addition, solar cells with larger areas can be produced.

Postdoctor Rui Zhang in the laboratory
“Our results now open for the manufacture of organic solar cells at larger scales for outdoor use“, says postdoc Rui Zhang. Olov Planthaber
This is a major step towards large-scale industrial manufacture of efficient and stable organic solar cells”, says Feng Gao, professor in the Department of Physics, Chemistry and Biology (IFM) at Linköping University.

The result has been published in Nature Energy.

Developments in organic solar cells are rapid, and the maximum energy efficiency achieved by solar cells produced in the laboratory is currently over 18%. The energy efficiency measures how large a fraction of the energy in sunlight is converted to useful energy in the solar cells. The efficiency limit is considered to be around 24% for organic solar cells.

Green solvents

One challenge is to manufacture organic solar cells that are sufficiently stable to function for ten years or more. Another challenge is that the highest energy is achieved in solar cells manufactured in solutions that contain toxic solvents, with a relatively low boiling point. The low boiling point causes problems during the manufacture, since the solution Rui Zhang holding a small solar cellRui Zhang with the new solar cell. Photo credit Olov Planthaberevaporates slightly too rapidly. The use of more eco-friendly solvents with higher boiling points leads immediately to a decrease in energy efficiency. This is a dilemma that researchers all over the world are working to solve.

These problems have now been solved in a joint project led by researchers at Linköping University in Sweden and Soochow University in China.

They have managed to manufacture a solar cell, using a solution with a high boiling point and without any toxic ingredients, whose energy efficiency is better than 17%.
In addition, the green-solvent processed solar module with an area of 36 cm2 shows a power conversion efficiency over 14%. This is the highest efficiency reported to date for organic solar cell modules with an active area exceeding 20 cm2. Both of these breakthroughs are important for organic solar cell technology to make its commercial breakthrough at a large scale.

Outdoor use

“Our results now open for the manufacture of organic solar cells at larger scales for outdoor use“, says postdoc Rui Zhang, who works with Professor Feng Gao in the Electronic and Photonic Materials Division, Linköping University.

The function of organic solar cells has improved step-by-step. When sunlight in the form of photons is absorbed in an organic semiconducting donor, an “excited state” forms. Electrons jump to a higher energy level and create holes at the lower energy level, to which they are, however, still attracted. The electrons are not fully freed, and a photocurrent does not arise. The researchers conducted experiments in which they added various acceptor materials, which accept electrons and thus allow them to become free, giving rise to a photocurrent.

A couple of years ago, Chinese researchers developed a new acceptor material, named Y6, which can deliver high efficiency for organic solar cells.

The guest molecule

What the work described in this joint publication has now achieved is to find a guest molecule, known as BTO, that ensures that Y6 molecules in the solar cell are packed in such a close and stable manner in the green solvents that the photocurrent can be generated efficiently. Adding BTO also enables larger areas of the solar cells to be manufactured with high efficiency.

“Our strategy leads to clear design rules for optimising the interaction between organic donors and acceptors in multicomponent blends, meeting the critical requirements for future development of organic photovoltaic technology, says Professor Yaowen Li, Soochow University.

The article: A guest-assisted molecular-organization approach for >17% efficiency organic solar cells using environmentally friendly solvents, Haiyang Chen, Rui Zhang, Xiaobin Chen, Guang Zeng, Libor Kobera, Sabina Abbrent, Ben Zhang, Weijie Chen, Guiying Xu, Jiyeon Oh, So-Huei Kang, Shanshan Chen, Changduk Yang, Jiri Brus, Jianhui Hou, Feng Gao, Yaowen Li and Yongfang Li. Nature Energy 2021, DOI 10.1038/s41560-021-00923-5

Translated by George Farrants

Professor Feng Gao and postdoctor Rui Zhang are talking in a corridorFeng Gao and Rui Zhang Photo credit Olov Planthaber


From the lab to a commercial product – a long and difficult road

Researchers at Linköping University are working to create the material for the solar cells of the future. The goal is to produce a commercially viable product. An interdisciplinary research project is to try to find out what it takes.

Postdoctor Rui Zhang in the laboratory

Solar cell material can assist self-driving cars in the dark

Material used in organic solar cells can be used as light sensors in electronics. This is shown by researchers at LiU who have developed a type of sensor able to detect circularly polarised red light. Their study is published in Nature Photonics.

Two persons in a lab with a laserinstrument infront of them on a table full of cables.

Better cybersecurity with new material

Digital information exchange can be safer, cheaper and more environmentally friendly with the help of a new type of random number generator for encryption developed at LiU. The technology paves the way for a new type of quantum communication.

Latest news from LiU

Professor Mattias Lindahl is contributing to a global ISO standard

There are hundreds of definitions of circular economy in the world, which leads to confusion. A new ISO standard with a definition widely accepted and disseminated will remedy the situation.

Tre persons in lab coates.

Better neutron mirrors can reveal the inner secrets of matter

An improved neutron mirror has been developed by researchers at LiU by coating a silicon plate with extremely thin layers of iron and silicon mixed with boron carbide. It paves the way for better studies of materials.

Lonely child in silhouette.

Lack of guidelines on care for children subjected to sexual abuse

Only half of 34 surveyed European countries have national guidelines on how to provide health care and treatment to children who have been subjected to sexual abuse. This is shown in a study led by researchers at Barnafrid at Linköping University.