POSTECH Organic Electronics Laboratory, Department of Chemical Engineering , Pohang University of Science and Technology , Pohang 790-784 , Republic of Korea.
Centre for Plastic Electronics, Department of Chemistry , Imperial College London , London SW7 2AZ , U.K.
ACS Appl Mater Interfaces. 2018 Oct 24;10(42):36037-36046. doi: 10.1021/acsami.8b14020. Epub 2018 Sep 20.
To investigate the influence of donor molecule crystallinity on photovoltaic performance in all-small-molecule solar cells, two dithieno[2,3- d:2',3'- d']-benzo[1,2- b:4,5- b']dithiophene (DTBDT)-based small molecules, denoted as DTBDT-Rho and DTBDT-S-Rho and incorporating different side chains, are synthesized and characterized. The photovoltaic properties of solar cells made of these DTBDT-based donor molecules are systemically studied with the [6,6]-phenyl-C-butyric acid methyl ester (PCBM) fullerene acceptor and the O-IDTBR nonfullerene acceptor to study the aggregation behavior and crystallinity of the donor molecules in both blends. Morphological analyses and a charge carrier dynamics study are carried out simultaneously to derive structure-property relationships and address the requirements of all-small-molecule solar cells. This study reveals exciton decay loss driven by large-scale phase separation of the DTBDT molecules to be a crucial factor limiting photocurrent generation in the all-small-molecule solar cells incorporating O-IDTBR. In the all-small-molecule blends, DTBDT domains with dimensions greater than 100 nm limit the exciton migration to the donor-acceptor interface, whereas blends with PCBM exhibit homogeneous phase separation with smaller domains than in the O-IDTBR blends. The significant energy losses in nonfullerene-based devices lead to decreased J and fill factor values and unusual decrease in V values. These results indicate the modulation of phase separation to be important for improving the photovoltaic performances of all-small-molecule blends. In addition, the enhanced molecular aggregation of DTBDT-S-Rho with the alkylthio side chain leads to higher degrees of phase separation and unfavorable charge transfer, which are mainly responsible for the relatively low photocurrent when using DTBDT-S-Rho compared with that when using DTBDT-Rho. On the other hand, this enhanced molecular aggregation improves the crystallinity of DTBDT-S-Rho and results in its increased hole mobility.
为了研究给体分子结晶度对全小分子太阳能电池光伏性能的影响，合成并表征了两种基于二噻吩并[2,3-d:2',3'-d']-苯并[1,2-b:4,5-b']二噻吩（DTBDT）的小分子，分别表示为 DTBDT-Rho 和 DTBDT-S-Rho，并引入了不同的侧链。用[6,6]-苯基-C-丁酸甲酯（PCBM）富勒烯受体和 O-IDTBR 非富勒烯受体系统地研究了基于这些 DTBDT 的给体分子制成的太阳能电池的光伏性能，以研究给体分子在这两种共混物中的聚集行为和结晶度。同时进行形貌分析和载流子动力学研究，以得出结构-性能关系，并满足全小分子太阳能电池的要求。这项研究表明，由 DTBDT 分子的大规模相分离引起的激子衰减损失是限制包含 O-IDTBR 的全小分子太阳能电池中光电流产生的关键因素。在全小分子共混物中，尺寸大于 100nm 的 DTBDT 域限制了激子向给体-受体界面的迁移，而与 PCBM 共混的共混物表现出较小的相分离，相分离域小于与 O-IDTBR 共混的共混物。基于非富勒烯的器件中的能量损失较大，导致 J 和填充因子值降低以及 V 值异常下降。这些结果表明，相分离的调制对于提高全小分子共混物的光伏性能很重要。此外，带有烷基硫侧链的 DTBDT-S-Rho 的分子聚集增强导致更高程度的相分离和不利的电荷转移，这主要导致使用 DTBDT-S-Rho 时的光电流相对较低，而使用 DTBDT-Rho 时的光电流较高。另一方面，这种增强的分子聚集提高了 DTBDT-S-Rho 的结晶度，并导致其空穴迁移率增加。
