New findings pave the way for stable organic solar cells that may enable cheap and renewable electricity generation

Newswise —

As solar cells crafted from carbon-based semiconductors are becoming more efficient at transforming sunlight into electricity, enhancing the enduring durability of these photovoltaic gadgets has become an increasingly crucial issue. In order to cater to the demands of real-world applications, the effectiveness of the photovoltaic tool must be maintained for an extensive period. To tackle this fundamental predicament, scientists have scrutinized the deterioration mechanisms for the pair of constituents utilized in the light-engrossing stratum of organic solar cells: the 'electron donor' and 'electron acceptor' substances. These two elements are necessary to dissociate the combined electron-hole pair produced after the assimilation of a photon into the unbound electrons and holes that make up electrical current.

In a recently published research article in the journal Joule, a group of global scientists led by the Cavendish Laboratory at the University of Cambridge has examined, for the first time, the deterioration pathways of both the electron donor and electron acceptor materials. The comprehensive analysis of the electron donor substance differentiates the current research from prior studies and presents crucial fresh perspectives for the discipline. Specifically, the detection of a rapid deactivation mechanism that is exclusive to the electron donor material has not been previously noted, and it introduces a novel aspect to consider when studying material degradation in organic solar cells.

The team at the Cavendish Laboratory collaborated with scientists from the United Kingdom, Belgium, and Italy to investigate the degradation of these materials. To accomplish this, they conducted photovoltaic device stability experiments, subjecting the operating solar cell to intense light that closely mimics sunlight, and combined this with ultrafast laser spectroscopy performed at Cambridge. The laser technique enabled the identification of a novel degradation mechanism in the electron donor material that involves polymer chain twisting. Consequently, when the twisted polymer absorbs a photon, it undergoes an exceedingly rapid deactivation pathway within femtosecond timescales (a millionth billionth of a second). This undesired process is quick enough to surpass the generation of free electrons and holes from a photon, which the researchers were able to relate to the reduced effectiveness of the organic solar cell after exposure to simulated sunlight.

Dr. Alex Gillett, the primary author of the study, stated that it was intriguing to discover that something as seemingly trivial as the twisting of a polymer chain could have such a significant impact on solar cell efficiency. He added that in the future, they intend to expand on their discoveries by working with chemistry teams to create new electron donor materials that have more inflexible polymer backbones. They aim to reduce the polymer's inclination to twist, resulting in a more stable organic solar cell device.

Organic solar cells possess distinctive characteristics that render them appropriate for a broad range of applications that conventional silicon photovoltaics cannot fulfill. These applications may include the development of electricity-generating windows for greenhouses that transmit the appropriate colours of light necessary for photosynthesis, or even photovoltaics that can be rolled up for simple transport and mobile electricity generation. By identifying the degradation mechanism that must be addressed, the present research paves the way for the next generation of photovoltaic materials and applications, bringing them closer to realization.