轮烷结构优化聚合物太阳能电池光伏性能★

doi:10.6023/A23070353

摘要/Abstract

聚合度高低会影响聚合物太阳能电池(PSC)活性层的共混微观结构, 导致其器件性能存在较大差异, 一般在聚合度较低时, PSC的能量转化效率(PCE)通常因电荷传输受到影响而明显降低. 为解决这一问题, 本工作将环状化合物冠醚与聚合物以非共价键的方式组成轮烷结构, 合成了四种具有不同冠醚含量且聚合度较低的给体材料PM6-C1、PM6-C2、PM6-C3和PM6-C4. 在保留聚合物本身优异光电性质的同时, 适量轮烷结构带来的非共价相互作用使活性层形成合适的纤维状网络结构和良好的相分离尺度, 增强了器件的电荷提取效率, 减少了陷阱/双分子复合, 从而导致高的电荷传输与收集效率. 基于PM6-C2的器件最终实现了16.23%的PCE, 高于基于PM6-L的器件(15.33%), 表明轮烷结构有助于改善聚合物太阳能电池活性层形貌, 在PSC材料研究中具有极大的潜力.

关键词: 聚合物太阳能电池, 非共价键, 轮烷结构, 冠醚, 相分离尺度

The degree of polymerization often affects the blending microstructure of the active layer in polymer solar cells (PSC), resulting in a large difference in device performance. Generally, when the degree of polymerization is low, the power conversion efficiency (PCE) of PSC is usually significantly reduced due to the impact of charge transport. To address this issue, we synthesized a series of polymer donors with rotaxane structure by introducing crown ether into the polymers, and four molecules PM6-C1, PM6-C2, PM6-C3 and PM6-C4 with different contents of crown ether were obtained. The rotaxane structure is composed of cyclic compounds and polymers through non-covalent bonds, which can affect intermolecular stacking by non-covalent interaction while retaining the excellent photoelectric properties of the polymer. The crown ether was randomly inserted into the backbone of polymer in the process of Stille coupling. By limiting the reaction time, the number-average molecular weight was guaranteed to be lower than 50 kDa. The devices and blend films based on the resultant polymers were characterized by means of external quantum efficiency (EQE), light intensity dependence, mobility, atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing incidence wide-angle X-ray scattering (GIWAXS), etc. In order to study the differences in device performance caused by the different introduction methods, the crown ether was directly added as an additive, and the open-circuit voltage (V_oc) and PCE of the device were significantly reduced. However, the device performance was different when the crown ether and the polymer backbone formed a rotaxane structure. Compared with PM6-L, the active layer based on PM6-C2 and Y6 exhibited an optimal fiber-like network structure and better phase separation scale, which contributed to better charge extraction efficiency and reduced trap/bimolecular recombination. Ultimately, more excellent short-circuit current density (J_sc) and fill factor (FF) were obtained because of high charge transport and collection efficiency. Therefore, the PM6-C2-based device achieved a PCE of 16.23%, exceeding that of the PM6-L-based device (15.33%). This work indicates that rotaxane structure is beneficial to improve the active layer morphology and show great potential in developing PSC materials.

Key words: polymer solar cells, non-covalent bond, rotaxane structure, crown ether, phase separation scale

引用此文

李东旭, 徐翔, 宋佳鸽, 梁松挺, 付予昂, 路新慧, 邹应萍. 轮烷结构优化聚合物太阳能电池光伏性能^★[J]. 化学学报, 2023, 81(11): 1500-1507.

Dongxu Li, Xiang Xu, Jiage Song, Songting Liang, Yuang Fu, Xinhui Lu, Yingping Zou. Rotaxane Structure Optimizes the Photovoltaic Performance of Polymer Solar Cells^★[J]. Acta Chimica Sinica, 2023, 81(11): 1500-1507.

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图/表 7

图1. PM6-C系列聚合物的合成步骤

Figure 1. Synthetic route of the PM6-C series polymers

图2. (a)给受体薄膜吸收曲线图和(b)聚合物给体能级图

Figure 2. (a) The normalized absorption spectra of polymer donors and acceptor in thin film state; (b) energy level diagram of polymer donors in this work

Polymer	λ_max^sol/nm	λ_max^film/nm	λ_onset^film/nm	E_g^opt/eV	HOMO/eV	LUMO/eV	E_g^cv/eV
PM6-L	609	614	684	1.81	–5.55	–3.38	2.17
PM6-C1	611	619	690	1.80	–5.54	–3.37	2.17
PM6-C2	613	620	688	1.80	–5.54	–3.37	2.17
PM6-C3	612	622	686	1.81	–5.53	–3.39	2.14
PM6-C4	612	620	685	1.81	–5.52	–3.40	2.12

表1. 聚合物的光学和电化学性质

Table 1. Optical and electrochemical properties of the polymers

图3. (a, f) PM6-L:Y6, (b, g) PM6-C1:Y6, (c, h) PM6-C2:Y6, (d, i) PM6-C3:Y6和(e, j) PM6-C4:Y6混合薄膜的AFM高度图和相应的相图(2 μm×2 μm)

Figure 4. AFM height images and the corresponding phase images of (a, f) PM6-L:Y6, (b, g) PM6-C1:Y6, (c, h) PM6-C2:Y6, (d, i) PM6-C3:Y6, and (e, j) PM6-C4:Y6 blend films (2 μm×2 μm)

图4. PM6-L:Y6、PM6-C1:Y6、PM6-C2:Y6、PM6-C3:Y6和PM6-C4:Y6共混膜的(a) 2D-GIWAXS测试图及(b) 相应的面内(红线)和面外(黑线)方向的1D线切剖面图

Figure 4. (a) The 2D GIWAXS patterns, and (b) corresponding in-plane (red) and out-of-plane (black) 1D integral curves of PM6-L:Y6, PM6-C1:Y6, PM6-C2:Y6, PM6-C3:Y6, and PM6-C4:Y6 blend films

Active layers	V_oc/V	J_sc/(mA•cm^-2)	J_sc-EQE/(mA•cm^-2)	FF/%	PCE/%
PM6-L:Y6	0.86 (0.85±0.01)	24.84 (24.53±0.50)	24.79	72.10 (70.75±1.50)	15.33 (15.10±0.23)
PM6-C1:Y6	0.84 (0.84±0.01)	24.81 (24.63±0.30)	24.20	75.47 (74.66±1.61)	15.82 (15.55±0.27)
PM6-C2:Y6	0.85 (0.84±0.01)	25.80 (25.56±0.33)	25.58	73.46 (72.66±1.22)	16.23 (16.02±0.21)
PM6-C3:Y6	0.85 (0.84±0.01)	25.13 (24.88±0.40)	24.99	75.63 (73.56±2.00)	16.08 (15.88±0.20)
PM6-C4:Y6	0.85 (0.84±0.01)	25.58 (25.28±0.36)	25.28	69.94 (68.30±1.70)	15.21 (14.99±0.22)

表2. 基于PM6-L和PM6-C系列给体的聚合物太阳能电池器件的光伏参数

Table 2. Photovoltaic parameters of PSC devices based on PM6-L and PM6-C series donors

图5. 以PM6-L, PM6-C系列聚合物和Y6制备器件的(a) J-V曲线图, (b) 外量子效率响应曲线, (c) 光电流与有效电压的特征曲线, (d) Voc与入射光强的特征曲线, (e) Jsc与入射光强的特征曲线和(f)空穴迁移率图

Figure 5. (a) The J-V curve, (b) the external quantum efficiency (EQE) response curve, (c) the plot of photocurrent against effective voltage characteristic curve, (d) the plots of open circuit voltage against incidence light intensity characteristic curve, (e) the short circuit current density against incidence light intensity characteristic curve, (f) the hole transport mobility (μh) of the blend films based on the PM6-L and PM6-C series polymers:Y6 blends

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