Merck Chemicals Ltd., Chilworth Technical Centre, University Parkway, SO16 7QD, Southampton, UK.
Phys Chem Chem Phys. 2015 May 7;17(17):11884-97. doi: 10.1039/c5cp01158b.
The impact of side-chain variations on the photothermal stability of solar cells containing poly(benzodithiophene-diketopyrrolopyrrole) polymers are investigated in the absence of oxygen. Four different side-chains of benzodithiophene (BDT) are synthesized and copolymerized with diketopyrrolopyrrole (DPP) by Stille polymerization. The photothermal stability is measured as active layer blends with phenyl-C61-butyric acid methyl ester (PCBM) in encapsulated inverted photovoltaic cell architecture with zinc oxide and
PSS as transport layers (ITO/ZnO/active layer/
PSS/Ag). Device degradation is correlated to the morphological behavior of the polymer:blend upon AM1.5 illumination (UV-visible light, 50 °C) and have been investigated by AFM, XRD, and UV-Vis. Once exposed to the light and to the temperature the BHJ stability is governed by two processes (i) PCBM crystallization and (ii) PCBM dimerization. Dimerization results in a rapid initial performance decrease followed by a more gradual decrease caused by a slower thermally activated crystallization. Depending on the blend morphology, dictated by the polymer's alkyl chain, the two processes occur to different extents thereby modulating the BHJ stability. Thus, of the polymer side-chains explored, linear alkyl side-chains stabilized the bulk heterojunction most effectively followed by no side-chain, alkoxy and branched side-chains. Lowering the concentration of fullerene in the active layer also reduces the rate of degradation across the polymers tested. This is a result of both the rate of crystallization and dimerization of fullerene being dependent on its concentration and the nature of the polymer side-chains. This approach appears to be a general strategy to increase the polymer:PCBM stability.
未通氧条件下，研究了侧链变化对含聚（苯并二噻吩-二酮吡咯吡咯）聚合物太阳能电池的光热稳定性的影响。合成了四种不同的苯并二噻吩（BDT）侧链，并通过 Stille 聚合与二酮吡咯吡咯（DPP）共聚。将光热稳定性作为活性层与苯基-C61-丁酸甲酯（PCBM）的混合物进行测量，在具有氧化锌和PEDOT：PSS 的封装倒光伏电池结构中作为传输层（ITO/ZnO/活性层/PEDOT：PSS/Ag）。通过原子力显微镜（AFM）、X 射线衍射（XRD）和紫外-可见光谱（UV-Vis）研究了器件降解与聚合物：混合物的形态行为之间的相关性。在 AM1.5 光照（UV-可见光，50°C）下暴露于光和温度后，BHJ 稳定性受到两个过程的控制：（i）PCBM 结晶和（ii）PCBM 二聚化。二聚化导致初始性能迅速下降，随后由于较慢的热激活结晶而导致更缓慢的性能下降。根据聚合物烷基链决定的共混物形态，两种过程的发生程度不同，从而调节 BHJ 稳定性。因此，在所研究的聚合物侧链中，线性烷基侧链最有效地稳定了本体异质结，其次是无侧链、烷氧基和支链侧链。降低活性层中富勒烯的浓度也会降低测试聚合物的降解速率。这是由于富勒烯的结晶和二聚化速率取决于其浓度和聚合物侧链的性质。这种方法似乎是提高聚合物：PCBM 稳定性的一般策略。
