Researchers have developed and created a new organic semiconductor specifically for organic solar cells (OSCs). By incorporating particular side units into their structure, they have managed to enhance the separation of frontier molecular orbitals, which results in a reduced exciton binding energy and improved power conversion efficiency. This fine-tuning of the acceptor component’s design is anticipated to boost the effectiveness of OSCs, paving the way for more efficient large-scale photovoltaic systems and innovative devices.
Organic solar cells (OSCs) offer a promising alternative to conventional inorganic solar cells, boasting numerous features that position them as vital contributors to a sustainable future. One key aspect is their tunable chemistry, enabling scientists to precisely modify the properties of chemical systems to achieve specific results. Recently, researchers from Japan have fine-tuned OSCs to enhance their power conversion efficiency.
In a recent study published in Angewandte Chemie International Edition, scientists from Osaka University have reported a new organic semiconductor that surpasses the established standards in power conversion efficiency.
OSCs are lightweight, flexible, and can be produced affordably in large quantities. This makes them highly suitable for applications like agrivoltaics, which enables the simultaneous cultivation of crops while harnessing solar energy to generate electricity over large land areas.
Typically, OSCs comprise two organic semiconductors — one known as the acceptor that transports charge carriers called electrons, and another called the donor that transports the remaining carriers known as holes. Current flows through a semiconductor when excitons, which are pairs of electrons and positive holes, separate into these charge carriers, forming electron-hole pairs. Although excitons are typically tightly bound together, sunlight with sufficient energy can dissociate them, generating a current.
“Lowering the energy required to break apart an exciton — referred to as exciton binding energy — facilitates the conversion of light into the desired electrical current,” explains the study’s lead author, Seihou Jinnai. “Therefore, we concentrated on factors that influence the binding energy, one being the distance between the electron and the hole. By increasing this distance, the binding energy is expected to decrease.”
The researchers designed a molecule that features side units capable of distancing the parts of the molecule that hold the electron and hole. This newly synthesized molecule was utilized as an acceptor in a bulk heterojunction OSC alongside a donor material, resulting in increased power conversion efficiency compared to the established standards. Furthermore, the molecule was tested as a standalone component of an OSC and exhibited superior light-to-current conversion.
“The molecule we developed demonstrates that the characteristics of side units in acceptor molecules play a crucial role in exciton behavior and overall efficiency,” notes senior author Yutaka Ie. “These results underline the significant achievements possible through the tailored chemistry of OSCs.”
The research findings highlight the potential of intentionally designing organic semiconductors and are expected to give rise to new devices, including high-performance OSCs and wavelength-selective transparent OSCs. Overall improvements in OSC performance are also expected to bolster their capabilities in large-scale photovoltaic applications, ultimately contributing to renewable energy solutions.
