School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China.
Phys Chem Chem Phys. 2014 Jan 7;16(1):311-23. doi: 10.1039/c3cp53268b.
An effective way to improve the efficiency of organic solar cells is to adjust the electron-withdrawing strength in donor-acceptor (D-A) copolymers. To achieve this goal, starting from previously reported polymers (PCPDT-BT and PDTPr-FBT) which are based on benzothiadiazole (BT) electron-deficient unit connected to each of two electron-rich units (cyclopentadithiophene (CPDT) and dithienopyrrole (DTPr)), we introduced two strong electron-withdrawing fluorine atoms or a cyano group on the BT unit to replace BT with fluorinated BT (FBT) and cyano BT (CNBT) in PCPDT-BT and PDTPr-FBT, respectively, and designed two types of D-A copolymers with different electron-withdrawing strengths. From the calculated results, the introduction of strong electron-withdrawing groups onto the copolymer can not only obviously reduce the HOMO and LUMO level of molecules, which results in increasing the open circuit voltage (Voc) in solar cells, but can also enhance light-absorbing efficiency and charge transport ability of polymers. In the meantime, the cyano copolymers of PCPDT-1CNBT and PDTPr-1CNBT show the best performances with the smallest band gaps, lowest HOMO energy levels, the highest Voc, and the largest hole mobility (3.67 × 10(-3) cm(2) V(-1) s(-1) and 8.05 × 10(-4) cm(2) V(-1) s(-1), respectively) among all the considered systems. The power conversion efficiencies (PCEs) of ~7.2% and ~6.8% for organic solar cell made of designed polymers (PCPDT-1CNBT and PDTPr-1CNBT) are predicted by Scharber models. We presented several polymer donors for comparison of how the strong electron-withdrawing group influences the electronic properties and optical absorption of the polymers and the performances of organic solar cells made of the polymers, thereby obtaining promising organic solar cells with high power conversion efficiencies.
提高有机太阳能电池效率的有效方法是调整给体-受体（D-A）共聚物中的电子受主强度。为了实现这一目标，我们从先前报道的聚合物（PCPDT-BT 和 PDTPr-FBT）出发，这些聚合物基于苯并噻二唑（BT）缺电子单元，分别与两个富电子单元（环戊二噻吩（CPDT）和二噻吩并吡咯（DTPr）相连），我们在 BT 单元上引入了两个强吸电子氟原子或氰基取代 BT，分别得到 PCPDT-BT 和 PDTPr-FBT 中的氟化 BT（FBT）和氰基 BT（CNBT），并设计了两种具有不同电子受主强度的 D-A 共聚物。从计算结果来看，将强吸电子基团引入共聚物不仅可以明显降低分子的 HOMO 和 LUMO 能级，从而增加太阳能电池中的开路电压（Voc），还可以提高聚合物的光吸收效率和电荷传输能力。同时，PCPDT-1CNBT 和 PDTPr-1CNBT 的氰基共聚物具有最小的带隙、最低的 HOMO 能级、最高的 Voc 和最大的空穴迁移率（3.67×10(-3)cm(2)V(-1)s(-1)和 8.05×10(-4)cm(2)V(-1)s(-1)），在所有考虑的体系中表现出最佳性能。通过 Scharber 模型预测，由设计的聚合物（PCPDT-1CNBT 和 PDTPr-1CNBT）制成的有机太阳能电池的功率转换效率（PCE）约为 7.2%和 6.8%。我们提出了几种聚合物供体进行比较，以了解强吸电子基团如何影响聚合物的电子性质和光吸收以及聚合物制成的有机太阳能电池的性能，从而获得具有高功率转换效率的有前途的有机太阳能电池。
