Donor–spacer–acceptor monodisperse conjugated co-oligomers for efficient single-molecule photovoltaic cells based on non-fullerene acceptors
作者:Jianfei Qu、Bingrong Gao、Hongkun Tian、Xiaojie Zhang、Yan Wang、Zhiyuan Xie、Haiyu Wang、Yanhou Geng、Fosong Wang
DOI:10.1039/c3ta14701k
日期:——
The current challenges for efficient bulk heterojunction (BHJ) organic photovoltaics (OPVs) based on organic/polymeric (non-fullerene) acceptors involve difficult control of neat phase separation in the nanoscale, severe geminate charge recombination, etc. Herein, a new molecular design concept, that is to construct donorâspacerâacceptor (DâSâA) co-oligomers with self-assembly properties, is proposed in order to realize ideal film morphology and manipulate the exciton dissociation and geminate charge recombination processes simultaneously. Three DâSâA co-oligomers, i.e.F5T8P-C2, F5T8P-C4 and F5T8P-C6 with oligo(fluorene-alt-bithiophene), perylene diimide (PDI) and alkyl as D-, A- and S-segments, respectively, were synthesized. All three DâSâA co-oligomers can form DâA alternating lamellar nanostructures with periods of â¼15 nm, an ideal nanostructure for BHJ OPVs. Compared to DâA co-oligomer F5T8-epP in which the D- and A-segments are directly connected without the alkyl spacer, the DâSâA co-oligomers not only show higher electron mobilities due to closer packing of PDI moieties, but also exhibit longer lifetimes of the charge-transfer states that can potentially restrain the geminate charge recombination and improve the charge generation efficiency. Accordingly, the single-molecule photovoltaic cells based on the DâSâA co-oligomers exhibit an improved fill factor of 0.47 and a high open-circuit voltage of 1.04 V. In particular, an external quantum efficiency of â¼65%, which is the highest for BHJ OPVs based on non-fullerene acceptor materials, has been demonstrated. By further extending the absorption onset of DâSâA co-oligomers to â¼600 nm, a single-molecule photovoltaic device with a power conversion efficiency of 2.70% has been fabricated. These results prove that high-efficiency BHJ OPVs based on non-fullerene acceptors are achievable if both the film morphology of the DâA blend and DâA interfaces are suitably manipulated.
目前,基于有机/聚合物(非富勒烯)受体的高效体异质结(BHJ)有机光伏器件(OPV)所面临的挑战包括难以控制纳米尺度的整齐相分离、严重的宝石电荷重组等。在此,我们提出了一种新的分子设计理念,即构建具有自组装特性的给体-间隔体-受体(DâSâA)共聚物,以实现理想的薄膜形态,并同时操纵激子解离和宝石电荷重组过程。研究人员合成了三种 DâSâA 共配体,即 F5T8P-C2、F5T8P-C4 和 F5T8P-C6,它们的 D 段、A 段和 S 段分别是低聚(芴-盐基噻吩)、过二亚胺(PDI)和烷基。三种DâSâA共配体都能形成周期为§¼15 nm的DâA交替片状纳米结构,这是BHJ OPV的理想纳米结构。DâSâA共聚物的D段和A段直接相连,没有烷基间隔物,与DâA共聚物F5T8-epP相比,DâSâA共聚物不仅由于PDI分子的紧密堆积而显示出更高的电子迁移率,而且电荷转移态的寿命也更长,从而有可能抑制宝石电荷重组,提高电荷生成效率。因此,基于DâSâA共配体的单分子光伏电池的填充因子提高到了0.47,开路电压高达1.04 V。通过进一步将DâSâA共配体的吸收起始波长延长至§¼600 nm,制备出了功率转换效率为2.70%的单分子光伏器件。这些结果证明,如果对DâA共聚物的薄膜形态和DâA界面进行适当处理,基于非富勒烯受体的高效BHJ OPV是可以实现的。