富勒烯聚集抑制双分子穿插构建聚合物/富勒烯互穿网络结构

In polymer solar cells (PSCs) based on bulk heterojunction (BHJ) materials comprising π-conjugated polymers with weak crystallinity and fullerene derivatives, the polymer has a poor self-organized ability, limiting the thickness of active layer. In addition, fullerene molecules could intercalate into the spaces of polymer side chains to form an intercalated structure, which would inhibit the phase separation and result in an impure domain. In this project, mixed-solvent vapor annealing was employed to construct the interpenetrating network structure. The aggregation of PC70BM was promoted, which inhibited the intercalation behavior, resulting in a continuous electron path and improved phase purity. The self-organized ability of polymer was enhanced as well due to the improved conformational transition of polymer chains and the inhibited ordered stacking of polymer side chains. As a result, a continuous electron path and improved phase purity. In addition, the effect of polymer structure and fullerene size on intercalated behavior in blend system would be also investigated through the molecular structure design. Moreover, the influence of polymer crystallinity and phase purity on the carrier mobility, the recombination of charge transfer state and the life time of mobile carriers would be also illustrated. Finally, we would establish the relationship among molecular structure, the morphology of blend films, microphysics mechanism and device performance.

弱结晶性共轭聚合物/富勒烯共混体系光伏电池中，聚合物与富勒烯之间存在双分子穿插现象，抑制相区纯度及相分离发生，不利于电荷转移态分离及载流子传输；同时，聚合物自组织能力差，限制空穴迁移，不利于提高光伏电池有源层厚度。本项目中，提出利用混合蒸汽处理方案，通过促进富勒烯分子聚集成核及扩散生长，利用富勒烯结晶抑制双分子穿插，促进相分离发生；通过提高聚合物分子构象转变能力、抑制聚合物侧链有序堆叠等促进聚合物有序排列，构建纳米级互穿网络结构。另外，通过改变PCDTBT分子侧链结构及富勒烯分子结构，研究聚合物分子结构、富勒烯分子尺寸对共混体系双分子穿插结构的影响；研究相区有序堆叠程度、相区纯度对电荷转移态分离效率及载流子寿命的影响，建立分子结构-薄膜形貌-微观物理机制-器件性能间的关系。

聚合物/富勒烯体系有机薄膜光伏电池有源层形貌与光伏电池性能密切相关。窄带隙材料侧链间自由体积通常较大，富勒烯便能够穿插进入聚合物侧链间，形成双分子穿插结构。双分子穿插行为是把双刃剑，存在双分子穿插可增加给受体界面面积，利于激子扩散；然而却形成了大量共混相，抑制形成双连续通路，不利于电荷转移态分离及载流子传输。针对以上问题，本项目通过调节双分子穿插程度，揭示了双分子穿插程度与互穿网络结构形成及共混相含量间相互关系，为进一步优化器件性能奠定基础。结论如下：（1）通过促进聚合物聚集或富勒烯聚集均可抑制形成双分子穿插结构；提出利用溶液记忆效应促进聚合物聚集、利用结晶诱导相分离原理促进富勒烯聚集，抑制双分子穿插，构筑互穿网络结构形成。（2）研究了聚合物结晶尺寸及双分子穿插程度对共混相含量的影响，建立共混相含量对激子扩散效率、电荷转移态分离效率的影响，建立薄膜形貌-器件性能间内在关联。