| With the increase of global population,fossil energy consumption is also increasing.Solar energy is considered as one of the most promising clean energy in the future because of its unique advantages,such as renewable,green,pollution-free and rich sources.In all kinds of solar cell,organic solar cells(OSCs)have received widespread attention due to their simple structure,low cost,light weight and flexibility.In the past several years,with the emergence of non fullerene acceptor including ITIC,Y6 and their derivatives have boosted the power conversion efficiency(PCE)of OSCs exceeding 18%.The improvement of OSCs device performance is not only due to the research and development of materials,but also closely related to the optimization of device structure and morphology.This paper mainly focuses on the effects of the photoelectric physical properties of polymer donor materials and device preparation methods on the performance of photovoltaic devices.The achievements were shown as follows:1)Research on the mechanism of polymer solubility affecting the photovoltaic performance of layer-by-layer processed organic solar cells: PNTB6-Cl does not dissolve in chloroform.PNTB6-Cl:N3 based LBL devices exhibited a efficiency of17.59 %,much higher than 15.24% for PNTB-Cl:N3 based devices and 16.20% for control devices based on PM6:N3.Importantly,excellent batch-to-batch reproducibility of PNTB6-Cl overcome the notorious batch-dependent issue in polymer donors,indicating PNTB6-Cl is a promising polymer donor for LBL-OSCs.The mechanism of polymer solubility affecting the performance of photovoltaic devices is revealed: the PNTB6-Cl film could tolerate the chloroform deposition of electron acceptors by washing away the polymers only in the amorphous region because of insolubility,resulting in LBL films with a much smoother surface and more efficient PL quenching.However,the chloroform processing dissolved the PNTB-Cl in both amorphous and crystalline regions,which was unfavorable for phase separation.Our studies demonstrate that the solubility property of a polymer could significantly impact electron acceptor penetration,phase separation and photovoltaic performance of LBLOSCs,which provide the guidelines for high-performance polymer donor design.2)Revealing the structure-performance-stability relations is crucially important for rational design of polymer donors.Enhancing π-π stacking by improving planarity is the most commonly used strategy in the design of polymer donor materials.Different from this strategy,this work reveals that enhancing the intermolecular interaction of polymers can significantly improve PCE and the thermal stability of devices.Due to the distortion of conjugated chains,polymer conjugated chains based on NTI are stacked through weak interatomic interaction rather than π-π stacking.Reducing the bulkiness of alkyl chain in NTI significantly affect the strength of short interaction between C=O and H-C,lead to PNTB-HD with stronger intermolecular interaction that endows the polymer with more condensed packing and stronger tendency to preassembly in chloroform solution,resulting in efficient photoluminescence quenching,favorable morphology,and higher hole/electron mobility.Therefore,the PNTB-HD: N3 based OSC exhibits the highest PCE of 18.15 %,which is much higher than 16.77% and 16.28% for PNTB-2T:N3 and PM6:N3 based devices.Importantly,82.9 % initial efficiency was maintained for PNTB-HD:N3 after contentiously thermal annealing at 65 ℃ for 128 h,while those for PNTB-2T:N3 was 73.1%.This study shows that introducing highly electronegative atoms into polymeric monomers and promoting the formation of stronger intermolecular interaction is a new strategy for the synthesis of high-performance polymer donor materials,which plays an important guiding role in the development of efficient and thermally stable OSCs polymer donors in the future. |
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