Elucidating the impact of molecular weight on morphology, charge transport, photophysics and performance of all-polymer solar cells
Elucidating the impact of molecular weight on morphology, charge transport, photophysics and performance of all-polymer solar cells
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DOI：
10.1039/d0ta08195g
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发表时间：
2020-10
影响因子：
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通讯作者：
Duyen K. Tran;Amélie Robitaille;I. J. Hai;Xiao Ding;Daiki Kuzuhara;T. Koganezawa;Yu‐Cheng Chiu;
中科院分区：
文献类型：
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作者：
Duyen K. Tran;Amélie Robitaille;I. J. Hai;Xiao Ding;Daiki Kuzuhara;T. Koganezawa;Yu‐Cheng Chiu;
了解聚合物分子量对聚合物太阳能电池的形态、物理和光伏特性的影响，对于进一步推进大规模应用的材料和器件的设计、加工、性能和优化至关重要。我们通过直接杂芳基化聚合合成了六种数均分子量（Mn）值（21-127 kDa）的双硒吩-萘二酰亚胺共聚物（PNDIBS），并利用它们研究了受体聚合物分子量对基于PNDIBS和供体聚合物PBDB-T的全聚合物太阳能电池（all-PSC）的电荷传输、共混物物理、共混物形态和光伏性能的影响。发现PBDB-T：PNDIBS共混物装置的短路电流和功率转换效率（PCE）随着Mn的增加而增加，直到在55 kDa的最佳分子量处达到峰值，然后随着Mn的进一步增加而降低。在最佳Mn值为55 kDa时观察到的最大PCE为10.2%，与此临界分子量下的最佳共混物电荷传输特性、共混物物理学和共混物形态相一致。与在55 kDa处观察到的具有主要面向分子取向的约5.5-6.5 nm结晶域的双连续网络相比，在较高Mn下具有较大尺度相分离的相对无序的微结构是明显的，而在21 kDa处观察到更精细堆积的结晶域。发现器件效率对有源层厚度的敏感性也取决于PNDIBSMn值。这些结果突出了调节聚合物组分的分子量以优化全聚合物太阳能电池的形态、电荷传输、光物理和效率的重要性。这些结果也为一种有前途的n型半导体共聚物的结构-性能关系提供了新的见解。
Understanding the influence of polymer molecular weight on the morphology, photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, performance and optimization of the materials and devices for large scale applications. We have synthesized six number-average molecular weight (Mn) values (21–127 kDa) of biselenophene–naphthalenediimide copolymer (PNDIBS) via direct heteroarylation polymerization and used them to investigate the effects of the acceptor polymer molecular weight on the charge transport, blend photophysics, blend morphology, and photovoltaic properties of all-polymer solar cells (all-PSCs) based on PNDIBS and the donor polymer PBDB-T. The short-circuit current and power conversion efficiency (PCE) of the PBDB-T:PNDIBS blend devices were found to increase with increasing Mn until reaching peaks at an optimal molecular weight of 55 kDa and then decreased with further increases in Mn. The maximum PCE of 10.2% observed at the optimal Mn value of 55 kDa coincided with optimal blend charge transport properties, blend photophysics, and blend morphology at this critical molecular weight. Compared to the bi-continuous network of ∼5.5–6.5 nm crystalline domains with predominantly face-on molecular orientations observed at 55 kDa, a relatively disordered microstructure with larger scale phase separation was evident at higher Mn while more finely packed crystalline domains were seen at 21 kDa. The sensitivity of the device efficiency to the active layer thickness was found to also depend on the PNDIBSMn value. These results highlight the importance of tuning the molecular weight of the polymer components to optimize the morphology, charge transport, photophysics and efficiency of all-polymer solar cells. The results also provide new insights on structure–property relationships for a promising n-type semiconducting copolymer.