D-A共聚高分子使用簡易的策略調控溶解度與固態結構形貌

Abstract

近年來，共軛高分子作為主體的有機太陽能元件發展常受限於溶解度，以Benzodithiophene與Difluorobenzothiadiazole的共聚高分子 (BDT-FBT)體系為例 ，由於高分子主鏈結構平直因此有強烈分子間作用力致使本身溶解度極差，即便修飾碳鏈也無法解決溶解度的問題。因此本研究發展一個簡便的共聚策略調控並優化現有的D-A共聚高分子的分子特性與固態結構形貌，藉由共聚策略修飾轉折子在高分子主鏈上調控其溶解度。 本研究分析轉折子的種類與位置對BDT-FBT 共軛高分子的光電性質與溶解度及固態結構的影響，使用轉折子-T、-Bz、-TEH合成出PBF-TF、PBFB-T、PBFB-Bz、PBFB-TEH四個共軛高分子。PBF-TF有優良吸光性質與固態結構排列，但是溶解度仍然很差；PBFB-T有足夠的溶解度，在高分子太陽能元件的光電轉換效率為1.94%，開路電壓為0.84 V; PBFB-Bz有彎曲的高分子主鏈使溶解度大幅上升，卻也嚴重破壞固態結構排列，不利於製作成太陽能元件；PBFB-TEH有優良溶解度之外亦能保有良好的固態結構排列，因此在高分子太陽能元件的光電轉換效率為2.73%，開路電壓為0.86 V。

Recently, the developments of some well-performed copolymers have been limited. Because the straight backbone facilitates strong intermolecular interactions which leads to poor solubility. Such as alternating benzodithiophene and difluorobenzothiadiazole copolymer (BDT-FBT).In addition, the modification of the alkyl chain also can't improve the solubility. As a result, we develop a facile copolymerization strategy to optimize the molecular properties and solid-state morphologies of D-A copolymers. Besides, the copolymerization strategy can adjust solubility by modifying the bender of the copolymer’s backbone. In this research, we focus on the bender’s type, the site of copolymer BDT-FBT, the impact of solubility and the solid-state morphology. We synthesize PBF-TF, PBFB-T, PBFB-Bz and PBFB-TEH polymers by using -T, -Bz, and -TEH as bender. PBF-TF polymer has excellent light-absorbing properties and solid-state arrangements but the solubility is poor. PBFB-T polymer has sufficient solubility and the PCE of solar cell is 1.94%, Voc = 0.84 V; The large curvature of the polymer backbone in PBFB-Bz enhances solubility but severely reduces the solid-state arrangement. PBFB-TEH polymer has not only good solubility but also regular solid-state arrangement. As a result, the PCE of solar cell is 2.73%, Voc = 0.86 V.