The intrinsic electronic structure of the donor and acceptor materials in the framework of the morphological features determine the output of organic solar cells (OSCs). Constructing the eutectic mixing based on the non-fullerene acceptors (NFAs) could fine-tune the bulk heterojunction (BHJ) thin film morphology as well as their electronic properties. With the formation of large amounts of crystallites, thin film crystallinity is greatly enhanced, accelerating the transportation of the free carriers. The JSC and FF amplification is achieved due to the formation of this kind of eutectic fibrillar lamellae structure, where efficient exciton dissociation occurs with reduced bimolecular and trap-assisted recombination. Suppressed non-radiative energy loss accounts for high VOC, enabling an improved power conversion efficiency (PCE) of 17.86%. These results reveal the basic importance of constructing a well-suited morphology to explore the details of the ultrafast photoelectric process and energy loss mechanism, which is of high demand in next episode OSC fabrication towards commercialization.
Single-layered organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) have been widely concerned attribute to the rapid progress in power conversion efficiency (PCE), which benefits from the continuous optimization of the electronic structure of the materials and the device structures. However, the performance of OSCs is still far behind other photovoltaic devices based on inorganic materials. One fundamental reason is the low charge mobility of organic materials and the complexity of non-equilibrium morphology of optical absorption layer. The next generation of NFA represented by Y6 shows better electronic structure, appropriate frontier energy levels and well matching with various donor materials. The efficiency of Y6-based OSCs has exceeded 18% and maintains a strong upward trend, envisaging a prosperous future for the OSC technology. As a derivative of Y6, the electronic structure of L8-BO was further optimized and the better morphology of the bulk heterojunction (BHJ) blends based on PM6:L8-BO improved the generation and transmission of carriers and reduced the charge recombination, achieving a PCE approaching 19%. The details of optimized multi-length scaled morphology is the key to improving device performance. In this optimized morphology framework, a global match between the photoelectric parameters and the characteristic lengths is realized, leading to effective exciton separation and the efficient carrier transport.
Double cascading energy level alignment is achieved in bulk heterojunction organic solar cells ensuring efficient carrier splitting and transport. This affords unique advantages in optimizing light absorption, exciton splitting, carrier transport, and charge transfer state energy levels in quaternary blends. Solar cell device power conversion efficiency up to 17.40%, the highest in single layered devices, was achieved. The optimization of the electronic structure and morphology resulted in a simultaneous improvement of the open circuit voltage, short circuit current and fill factor. The proper ancillary donor/acceptor material choice provides useful handles in thin film. Control of the electronic structure and charge transfer state energy level is achieved with the choice of donor and acceptor materials, allowing the manipulation of the hole-transfer rates, carrier transport, and non-radiative recombination losses. A detailed structure-property relationship that best manifests the impo
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