Nagatomo Takaaki, Vats Ajendra K, Matsuo Kyohei, Oyama Shinya, Okamoto Naoya, Suzuki Mitsuharu, Koganezawa Tomoyuki, Fuki Masaaki, Masuo Sadahiro, Ohta Kaoru, Yamada Hiroko, Kobori Yasuhiro
Department of Chemistry, Graduate School of Science, Kobe University, 1-1, Rokkodai-cho, Nada, Kobe657-8501, Japan.
Division of Materials Science, Graduate School of Science and Technology, Nara Institute of Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara630-0192, Japan.
ACS Phys Chem Au. 2022 Dec 30;3(2):207-221. doi: 10.1021/acsphyschemau.2c00049. eCollection 2023 Mar 22.
Recent remarkable developments on nonfullerene solar cells have reached a photoelectric conversion efficiency (PCE) of 18% by tuning the band energy levels in small molecular acceptors. In this regard, understanding the impact of small donor molecules on nonpolymer solar cells is essential. Here, we systematically investigated mechanisms of solar cell performance using diketopyrrolopyrrole (DPP)-tetrabenzoporphyrin (BP) conjugates of C4-DPP-HBP and C4-DPP-ZnBP, where C4 represents the butyl group substituted at the DPP unit as small p-type molecules, while an acceptor of [6,6]-phenyl-C-buthylic acid methyl ester is employed. We clarified the microscopic origins of the photocarrier caused by phonon-assisted one-dimensional (1D) electron-hole dissociations at the donor-acceptor interface. Using a time-resolved electron paramagnetic resonance, we have characterized controlled charge-recombination by manipulating disorders in π-π donor stacking. This ensures carrier transport through stacking molecular conformations to suppress nonradiative voltage loss capturing specific interfacial radical pairs separated by 1.8 nm in bulk-heterojunction solar cells. We show that, while disordered lattice motions by the π-π stackings via zinc ligation are essential to enhance the entropy for charge dissociations at the interface, too much ordered crystallinity causes the backscattering phonon to reduce the open-circuit voltage by geminate charge-recombination.
近期，非富勒烯太阳能电池取得了显著进展，通过调节小分子受体中的能带能级，其光电转换效率（PCE）已达到18%。在这方面，了解小分子给体对非聚合物太阳能电池的影响至关重要。在此，我们系统地研究了使用C4-DPP-HBP和C4-DPP-ZnBP的二酮吡咯并吡咯（DPP）-四苯并卟啉（BP）共轭物作为小分子p型分子的太阳能电池性能机制，其中C4表示在DPP单元上取代的丁基，同时使用了[6,6]-苯基-C-丁酸甲酯作为受体。我们阐明了在供体-受体界面处由声子辅助的一维（1D）电子-空穴解离引起的光载流子的微观起源。使用时间分辨电子顺磁共振，我们通过控制π-π供体堆叠中的无序来表征电荷复合。这确保了载流子通过堆叠分子构象传输，以抑制体异质结太阳能电池中捕获由1.8 nm分隔的特定界面自由基对的非辐射电压损失。我们表明，虽然通过锌连接的π-π堆叠产生的无序晶格运动对于增强界面电荷解离的熵至关重要，但过多的有序结晶度会导致反向散射声子通过双电荷复合降低开路电压。
