Non fullerene small acceptor molecules in organic photovoltaics are proven beneficial than the traditional fullerene based acceptors for their fine contribution in organic solar cells. Researchers are constantly doing efforts for designing novel acceptor materials with promising photovoltaic properties. Designing of novel molecules by end-capped modifications is a convenient strategy to obtain high efficiency acceptor molecules for OSCs. Herein, we studied optoelectronic characteristics of five novel acceptor–donor–core–donor–acceptor configured small acceptor molecules (S1–S5) after end-capped modifications of recently synthesized DF-PCIC molecule. Designed molecules S1–S5 consist of 1,4-difluorobenzene (as central core), 4,4-bis(2-ethylhexyl)-2,6-dimethyl-4H-cyclopenta[1,2-b:5,4-b′]dithiophene as donor which directly attached with different end-capped acceptors. The electronic and optical properties of newly designed (S1–S5) molecules are examined and compared with reference molecule with the aid of DFT and TD-DFT. Certain key parameters like frontier molecular orbitals analysis, density of states, dipole moment, binding energy along with transition density matrix, excitation energy, charge mobility, absorption maxima and charge transfer analysis have been performed in order to explore the photo-physical, optoelectronic and photovoltaic properties of designed and reference molecule. Out of newly designed structures, S4 displayed lowest energy band-gap (2.25 eV) with red-shifting in absorption spectrum (λmax = 712.43 nm) in chloroform which disclosed the perfect relationship between end-capped acceptor with large electron withdrawing character through extended conjugation. Similarly, S1 exhibited highest value (1.53 V) of open circuit voltage (Voc) with respect to PTB7-Th donor material owing to lower values of λe. Designed molecules exhibit better electron and hole mobility as compared to reference molecule R. All molecules express better absorption maximum, open circuit voltage, low excitation energies, comparable binding energies, large dipole moment and efficient electron and hole transport as compared to reference molecules. So, results these parameters suggest that end-capped modification is a convenient strategy in order to enhance the efficiency of OSCs. Therefore, conceptualized molecules are recommended to experimentalist for out-looking future developments of highly efficient solar cells.

中文翻译：

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A-D-C-D-A 配置的小分子受体 (SMA) 的分子工程，具有用于高效无富勒烯有机太阳能电池的光伏特性

有机光伏中的非富勒烯小受体分子被证明比传统的基于富勒烯的受体更有益，因为它们在有机太阳能电池中的贡献很好。研究人员一直在努力设计具有良好光伏特性的新型受体材料。通过封端修饰设计新分子是获得 OSC 高效受体分子的便捷策略。在此，我们研究了最近合成的 DF-PCIC 分子的封端修饰后五种新型受体-供体-核心-供体-受体配置的小受体分子（S1-S5）的光电特性。设计的分子 S1-S5 由 1,4-二氟苯（作为中心核）、4,4-双（2-乙基己基）-2,6-二甲基-4H-环戊二烯[1,2-b:5，4-b']二噻吩作为供体直接与不同的封端受体相连。在 DFT 和 TD-DFT 的帮助下，检查了新设计的 (S1-S5) 分子的电子和光学性质，并与参考分子进行了比较。某些关键参数如前沿分子轨道分析、状态密度、偶极矩、结合能以及跃迁密度矩阵、激发能、电荷迁移率、吸收最大值和电荷转移分析已经进行，以探索光物理、光电和设计和参考分子的光伏特性。在新设计的结构中，S4 显示出最低能带隙 (2.25 eV)，吸收光谱发生红移 (λmax = 712. 43 nm) 在氯仿中揭示了通过扩展共轭具有大吸电子特性的封端受体之间的完美关系。类似地，由于较低的λe值，S1相对于PTB7-Th供体材料表现出最高的开路电压（Voc）值（1.53 V）。与参考分子 R 相比，设计的分子表现出更好的电子和空穴迁移率。与参考分子相比，所有分子都表现出更好的吸收最大值、开路电压、低激发能、可比的结合能、大偶极矩以及有效的电子和空穴传输。因此，这些参数的结果表明封端修饰是提高 OSC 效率的便捷策略。所以，