Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, USA.
J Am Chem Soc. 2012 Jun 20;134(24):10071-9. doi: 10.1021/ja301460s. Epub 2012 Jun 6.
The tandem solar cell architecture is an effective way to harvest a broader part of the solar spectrum and make better use of the photonic energy than the single junction cell. Here, we present the design, synthesis, and characterization of a series of new low bandgap polymers specifically for tandem polymer solar cells. These polymers have a backbone based on the benzodithiophene (BDT) and diketopyrrolopyrrole (DPP) units. Alkylthienyl and alkylphenyl moieties were incorporated onto the BDT unit to form BDTT and BDTP units, respectively; a furan moiety was incorporated onto the DPP unit in place of thiophene to form the FDPP unit. Low bandgap polymers (bandgap = 1.4-1.5 eV) were prepared using BDTT, BDTP, FDPP, and DPP units via Stille-coupling polymerization. These structural modifications lead to polymers with different optical, electrochemical, and electronic properties. Single junction solar cells were fabricated, and the polymer:PC(71)BM active layer morphology was optimized by adding 1,8-diiodooctane (DIO) as an additive. In the single-layer photovoltaic device, they showed power conversion efficiencies (PCEs) of 3-6%. When the polymers were applied in tandem solar cells, PCEs over 8% were reached, demonstrating their great potential for high efficiency tandem polymer solar cells.
串联太阳能电池结构是一种有效的方法，可以收集更广泛的太阳光谱部分，并比单结电池更好地利用光子能量。在这里，我们设计、合成并表征了一系列新的低带隙聚合物，专门用于串联聚合物太阳能电池。这些聚合物的骨架基于苯并二噻吩 (BDT) 和二酮吡咯并吡咯 (DPP) 单元。烷基噻吩基和烷基苯基部分分别被引入到 BDT 单元上，形成 BDTT 和 BDTP 单元；呋喃部分被引入到 DPP 单元上，取代噻吩，形成 FDPP 单元。使用 BDTT、BDTP、FDPP 和 DPP 单元通过 Stille 偶联聚合制备了低带隙聚合物（带隙=1.4-1.5 eV）。这些结构修饰导致聚合物具有不同的光学、电化学和电子特性。制备了单结太阳能电池，并通过添加 1,8-二碘辛烷 (DIO) 作为添加剂来优化聚合物：PC(71)BM 活性层形貌。在单层光伏器件中，它们的功率转换效率 (PCE) 为 3-6%。当将这些聚合物应用于串联太阳能电池时，可达到 8%以上的 PCE，这表明它们在高效率串联聚合物太阳能电池中有很大的应用潜力。
