Organic solar cells with adjustable band gap height, light weight, flexibility, low cost, etc. are important development directions for next-generation photovoltaic technology. Organic solar cells are limited by the 'narrow absorption' characteristics of organic materials, binary blend films It is difficult to achieve effective wide-spectrum utilization of solar energy, and there is always a fundamental contradiction between phase blending (promoting exciton dissociation) and phase separation (favoring charge transport), which restricts the further breakthrough of the performance of organic photovoltaic devices. The solar cell maintains a single cell structure, and introduces a complementary third component in the binary active layer to enhance spectral absorption. Although the ternary battery has achieved certain success, it still faces severe challenges. The core problem lies in the three It is difficult to achieve clear and effective shape control of the meta-blend film to ensure efficient exciton dissociation and charge transfer at the same time. Therefore, it has been reported that the performance improvement of the ternary battery is low.
With the support of the National Natural Science Foundation of China, the Ministry of Science and Technology and the Chinese Academy of Sciences, Zhu Xiaozhang, a researcher at the Institute of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, used the researchers to develop a new thienothiophene-based photovoltaic receptor NITI (Adv. Mater.2017,29,1704510), rational selection of binary system, constructing a ternary active layer morphology with 'hierarchical structure', achieving a significant increase in photoelectric conversion efficiency, explaining the morphology of the photoelectric process and device parameters The decisive impact, the related paper was published in the journal Nature-Energy (DOI: 10.1038/s41560-018-0234-9).
The ternary blend films were selected from strong crystallization, wide band gap electron donor material BTR, weak crystallization, narrow band gap electron acceptor material NITI, and fullerene receptor PC71BM with strong aggregation and excellent electron transport properties. Favorable gradient electronic structure and complementary light absorption. Optimized by device, the above three components achieve the highest photoelectric conversion efficiency of 13.63% (average 13.20%) at the optimal film thickness of 300nm, and the performance of the two components is up to 51%. 100%, this is not only the highest performance record of all-small-cell solar cells, but also the best-performing thick film (>200nm) organic solar cells. Together with Shanghai Jiaotong University and the related research group of Linköping University in Sweden, they proposed a 'grading structure'. New ternary active layer morphology: NITI and BTR are highly blended to form a small phase separation fine structure that facilitates charge separation. PC71BM forms a large-scale phase separation structure and favorable face-on on the periphery of the BTR and NITI blending regions. Stacking. The researchers have demonstrated that NITI receptors play an important role in the photoelectric process. On the one hand, it inhibits the contact between BTR and PC71BM, enabling three components to acquire and two components (BTR). : NITI) equivalent low loss open circuit voltage; PC71BM forms an electron transport high-speed path in the active layer, effectively transporting NITI-separated electrons to the electrodes, thereby ensuring high external quantum efficiency (EQEs) and fill factor (FF) ) .
Overall, the work designed and realized the new morphology of the active layer of organic ternary cells, giving full play to the unique advantages of small molecules and fullerene electron acceptors in organic solar cells, while achieving high open voltage, high current And high filling factor, which provides a new idea for the regulation of the active layer morphology of organic ternary cells.
Figure 1. Chemical structure, energy level arrangement, absorption spectrum and device performance
Figure 2. Schematic diagram of hierarchical structure and performance statistics of organic solar cells
