【作者】 王伟；

【导师】 闵杰；

【作者基本信息】 武汉大学 ， 材料科学与工程， 2022， 博士

【摘要】 有机太阳能电池（OSCs）因其可溶液加工、质轻价廉等独特优势,在柔性可弯曲、半透明器件和便携式智能电子等方面具有广阔的应用前景而备受研究人员青睐。得益于活性层材料不断迭代和器件工艺的优化,有机太阳能电池的光电转换效率（PCE）稳步突破,现单节电池效率已突破到19.6%,但其稳定性并未随着效率的提升而有太大的改善,仍是限制其商业化进程的核心难题。相比于目前主流的小分子受体材料,单组分和聚合物受体材料在器件形貌、光和热稳定性等方面具有天然的优势,但因早期单组分和聚合物材料种类少、形貌优化难度大,器件效率仍处于较低水平。我们期待借助小分子受体材料演变历程中积累的合成和器件工艺优化的经验,将高性能的小分子受体材料单组分化和聚合物化,构建出新的小分子单组分材料和聚合物受体材料,最终获得高效且稳定的有机太阳能电池。主要成果如下:第二章工作中,我们基于两元体系中确定最优的给受体比例,然后再按照最优比例来设计并合成出D-A构型的寡聚噻吩-富勒烯小分子单组分材料Rh-PC₇₁BM。得益于Rh-PC₇₁BM高的激子解离效率和较平衡的电子/空穴迁移率,最终Rh-PC₇₁BM器件获得了3.22%的效率,为当时已报道的小分子单组分材料的最高效率,证明了借鉴体异质结器件的优化经验来指导单组分材料设计的可行性。重要的是,相比于体异质结体系Rh-OH:PC₇₁BM,Rh-PC₇₁BM器件表现出优异的热稳定性。在85℃下持续加热400 h,Rh-PC₇₁BM器件仍能保持初始效率的86%,而Rh-OH:PC₇₁BM器件在同样条件下只余初始值的16%,表明构建成单组分材料是提升富勒烯电池稳定性的一种有效途径。上一章中,单组分材料Rh-PC₇₁BM的吸收主要分布在400-700 nm,与太阳光谱的重合度低,导致器件的短路电流密度(J_SC)仅为7.50 m A cm^-2。第三章中,为进一步拓宽小分子单组分的吸收,我们用A-D-A型非稠环受体替代富勒烯受体,构建了两个给体单元不同的小分子单组分材料SW1和SW2。两个材料均表现出全谱吸收,在400-850 nm区间具有较强的光捕获能力。SW1单组分器件J_SC达到9.12 m A cm^-2,获得了3.78%的效率。但SW2的效率极低,仅为0.25%。为此我们详细分析了不同给体单元对单组分材料的光学吸收、能级、光-电转换物理机制和形貌的影响。此外,SW1和SW2器件具有优异的稳定性。无论是于氮气氛围中存储160 h,还是于一个光强下连续照射160 h,SW1和SW2器件均能保持初始值的90%以上。单组分材料SW1和SW2因其受体部分为非稠环骨架,导致电子迁移率较低,电荷复合严重,器件效率不高。第四章中,因Y系列受体可形成规整三维网状结构,我们将非稠环受体替换为Y系列受体,构建了两个给受体单元比例不同的小分子单组分材料SM-1Y和SM-2Y。相比于非稠环类单组分材料SW1,SM-1Y和SM-2Y的吸收进一步拓宽,在400-910 nm区间均具有良好的光捕获能力,而且电荷传输得到一定程度地改善。最终,SM-1Y的器件效率为2.51%,而SM-2Y的为6.22%,首次超过富勒烯类小分子单组分材料,为目前小分子单组分材料的最高效率。与此同时,SM-1Y和SM-2Y器件表现出优异的稳定性,在存储或光照300 h后仍能维持初始值的85%以上。第五章中,我们以Y5-C20为主骨架、噻吩为连接单元,通过D-A共聚构建了吸收范围广且消光系数高的聚合物受体材料PYT。与此同时,通过调节PYT分子量（PYT_L、PYT_M和PYT_H）对全聚合物活性层形貌进行精细调控以获得最佳形貌。研究发现中等分子量PYT_M与PM6共混时,取得的效率最高,为13.44%,PM6:PYT_L的次之,PM6:PYT_H的效率最差,仅为8.61%。值得指出的是PM6:PYT_M器件的J_SC和PCE均为当时全聚合物有机太阳电池的最高值,证明了从材料设计和形貌优化两方面着手提升全聚合物有机太阳电池效率思路的正确性。此外,我们从吸收、能级、激子解离、电荷传输、复合和收集、活性层形貌和能量损失等方面系统地探讨了PYT分子量影响器件效率的具体机理。上一章中,研究发现PM6对PYT分子量具有选择性,需精准控制PYT分子量才可获得最佳效率。但不同批次PYT的合成很难保证相同的分子量,存在批次性差异。在第六章中,我们搭建了一套在线光致发光光谱装置以实时监测PYT聚合过程中荧光光谱的变化,从而建立荧光光谱特征参数（峰位移、峰值和半峰宽中间值位移等）与PYT分子量之间的关系曲线。后续仅需监测聚合过程中荧光光谱的变化即可实现对PYT分子量的精准控制。此外,我们通过改变催化剂来源和单体批次对聚合过程施加一定的干扰,检验建立的荧光光谱与PYT分子量关系的可靠性。研究发现通过荧光光谱精准调控后所获得的PYT的效率在小范围内波动,基本可以满足工业化对产品品质的要求。本工作为聚合物光活性材料的分子量调控开辟了一种新颖和重要的技术手段。更多还原

【Abstract】 Solution-processed organic solar cells（OSCs）are appealing candidates in flexibility,semitransparency devices and portable electronic products,owing to their special merits of low-cost and light-weight.Thanks to the innovation of active materials and optimization of device process,the power conversion efficiency（PCE）of OSCs has made a steady breakthrough,and the PCE of a single-junction cell has reached 19.6%.However,the stability of OSCs has not been greatly improved,which is still the core problem limiting the commercialization process of OSCs.Compared with the mainstream small-molecular acceptors,single-component materials and polymer acceptors have inherent advantages in device morphological,photo and thermal stability.However,their efficiencies of devices are hampered by the lack of single-component materials and polymer acceptors,and difficulty of morphology optimization in the early stage.Learning from the considerable body of knowledge accumulated during the past two decades on the small molecular acceptors based OSCs,we utilize high-performance small molecular acceptors to construct new single-component materials and polymer acceptors,and finally obtain efficient and stable OSCs.According to this proposal,the main works were summarized as follows.In the second chapter,we first determined the optimal unit ratio of donor:acceptor in bulk heterojunction（BHJ）OSCs,and then designed and synthesized an oligothiophene-fullerene dyad Rh-PC₇₁BM with balanced D-A backbone.Benefitting from the high exciton dissociation efficiency and relatively balanced electron/hole mobility of Rh-PC₇₁BM single-molecular OSCs（SMOSCs）,the final efficiency of Rh-PC₇₁BM SCOSCs was 3.22%,which was the highest value reported at that time for SMOSCs.The success of Rh-PC₇₁BM proved the feasibility of drawing lessons from the optimization experience of BHJ device to guide the design of one-component materials.Importantly,compared to the corresponding Rh-OH:PC₇₁BM BHJ devices,Rh-PC₇₁BM devices demonstrated excellent thermal stability.After annealing at 85℃for400 h in nitrogen atmosphere,Rh-PC₇₁BM devices exhibited a PCE degradation down to 83%,while Rh-OH:PC₇₁BM devices displayed poorer thermal stability with a PCE loss down to around 16%at the same periods.In the previous chapter,the absorption of one-component material Rh-PC₇₁BM is mainly distributed at 400-700 nm,which coincide low with solar spectrum,resulting in the short circuit current density(J_SC)of the device is only 7.50 m A cm^-2.In the third chapter,to further broaden the absorption of molecular dyads,we introduced a non-fused ring non-fullerene acceptor as the acceptor segments to synthesize two molecular dyads,SW1 and SW2,with different donor units.Notably,the two dyads exhibited panchromatic absorption spectra within 400-850 nm.Impressively,the SW1 device demonstrateed an inspiring PCE of 3.78%with a high J_SC of 9.12 m A cm^-2.We believe this new strategy opens up the possibility for designing high-performance non-fullerene acceptor-based single-component photovoltaic materials.But SW2-based device was extremely inefficient,only 0.25%.Then,we systematically investigated the effect of different donor units on the optoelectronic properties,energy levels,photo-physical processes and morphology of two dyads,which may provide reference value for the selection of donor/acceptor units.In addition,SW1 and SW2-based devices had excellent stability.Both stored in nitrogen atmosphere and continuously light-soaking under one sun illumination,SW1 and SW2 devices can maintain more than 90%of the initial values.In the previous chapter,the acceptor segment is non-fused skeleton,which leads to low electron mobility,serious charge recombination,and low device efficiency.In the fourth chapter,considering that Y series acceptors tend to form a continuous and regular three-dimensional structure,we replaced the non-fused ring acceptor segment with Y series acceptor,and constructed two molecular dyads SM-1Y and SM-2Y with different donor/acceptor unit ratio.Compared to molecular dyad SW1,SM-1Y and SM-2Y have wider absorption with 400-910 nm and higher electron/hole mobility.The SM-1Y-based SMOSC exhibited a PCE of 2.51%.Impressively,the SM-2Y-based device demonstrated a much higher efficiency of 6.22%,which was the highest value reported for SMOSCs so far.It is the first time of the efficiency of non-fullerene acceptor based molecular dyads exceeds the fullerene-based counterparts.At the same time,SM-1Y and SM-2Y devices showed excellent stability.Both stored in nitrogen atmosphere and continuously light-soaking under one sun illumination for 300 h,SM-1Y and SM-2Y devices can maintain more than 85%of the initial values.In the fifth chapter,applying a fused-ring electron acceptor Y5-C20 as the key building block and thiophene as theπ-bridges,we designed and synthesized aπ-conjugated polymer acceptor PYT.PYT possessed broad absorption with a narrow band gap and high absorption coefficient.For fine-tuning the active layer morphology,we synthesized a series of PYT polymer acceptors with controlled M_n values（PYT_L、PYT_M and PYT_H）.When fabricated into all-polymer solar cells with PM6,it was observed a clear molecular weight dependence on device performance.Optimized devices based on PM6:PYT_L,PM6:PYT_M and PM6:PYT_H exhibits PCEs of 12.55%,13.44%and 8.61%,respectively.It is worth pointing out that the values of J_SC and PCE in PM6:PYT_M device are the highest values reported at that time for all-polymer solar cells（all-PSCs）.In addition,we systematically investigate the underlying impact of PYT’s molecular weight on the optoelectronic properties,energy levels,photo-physical processes,morphology and energy loss.In the previous chapter,when PM6 as the donor,the efficiency was sensitive to PYT molecular weight.However,different batches of PYT are difficult to ensure the same molecular weight during the reactions.In the sixth chapter,we set up an in-situ photoluminescence spectroscopy to real-time monitor the change of fluorescence spectrum during PYT polymerization,so as to establish the relationship curves between the characteristic parameters of fluorescence spectrum（peak wavelength、peak intensity and half peak wavelength,etc.）and PYT molecular weight.Then,the molecular weight of PYT can be accurately controlled just by monitoring the change of fluorescence spectrum during polymerization.In addition,the reliability of the established relationship was tested by changing the source of catalyst and monomer batch to interfere with the polymerization process.It was found that the efficiency of obtained PYT fluctuated in a small range,which can enough to meet the product quality requirements of industrialization,proving the feasibility of building a real-time monitoring device to control molecular weight of polymer materials.更多还原