基于苯并[2,1-b:3,4-b']二噻吩的低 HOMO 能级共轭聚合物用于有机光伏。
Conjugated polymers based on benzo[2,1-b:3,4-b']dithiophene with low-lying highest occupied molecular orbital energy levels for organic photovoltaics.
机构信息
Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290, USA.
出版信息
ACS Appl Mater Interfaces. 2009 Jul;1(7):1613-21. doi: 10.1021/am900327n.
Fusing bithiophene units with a benzo moiety, benzo[2,1-b:3,4-b']dithiophene (BDT), was projected by theoretical calculations to lower the highest occupied molecular orbital (HOMO) energy level of the resulting polymers compared with that of the bithiophene unit, which would enhance the open circuit voltage of bulk heterojunction photovoltaic cells fabricated from BDT-based polymers blended with PCBM. The homopolymer of BDT (HMPBDT) and alternating copolymer of BDT with 2,1,3-benzothiadiazole (PBDT-BT) were therefore synthesized and fully characterized. Both the homopolymer (HMPBDT) and the copolymer (PBDT-BT) were experimentally confirmed to have low HOMO energy levels (-5.70 eV for HMPBDT and -5.34 eV for PBDT-BT). Introducing the acceptor moiety (2,1,3-benzothiadiazole) successfully lowered the optical band gap of the copolymer from 2.31 eV (HMPBDT) to 1.78 eV (PBDT-BT). Bulk heterojunction photovoltaic devices were fabricated from blends of these structurally related polymers with PBCM to investigate the photovoltaic performances. The optimized device of HMPBDT:PCBM (1:3, 180 nm) exhibited an improved open circuit voltage (V(oc)) of 0.76 V, a short circuit current (J(sc)) of 0.34 mA/cm(2), and a fill factor (FF) of 0.40, offering an overall efficiency of 0.10%. The observed large phase separation of the thin film by AFM and the large band gap were accountable for the small current. The optimized device of PBDT-BT:PCBM (1:3, 55 nm) demonstrated a better efficiency of 0.6%, with V(oc) = 0.72 V, J(sc) = 2.06 mA/cm(2), and FF = 0.42. The much improved current was attributed to the lower bandgap and better film morphology. However, the low hole mobility limited the thickness of the PBDT-BT:PCBM film, making inaccessible the thicker film which would utilize more light and enhance the current. Further improvements are expected if the mobility and film morphology can be improved by the new materials design, together with low band gap and low HOMO energy level.
将噻吩单元与苯并部分融合，得到苯并[2,1-b:3,4-b']二噻吩（BDT），理论计算预测，与噻吩单元相比，所得聚合物的最高占据分子轨道（HOMO）能级将会降低，这将提高基于 BDT 的聚合物与 PCBM 共混制成的体异质结光伏电池的开路电压。因此，合成并完全表征了 BDT 的均聚物（HMPBDT）和 BDT 与 2,1,3-苯并噻二唑的交替共聚物（PBDT-BT）。实验证实，均聚物（HMPBDT）和共聚物（PBDT-BT）的 HOMO 能级均较低（HMPBDT 为-5.70 eV，PBDT-BT 为-5.34 eV）。引入受体部分（2,1,3-苯并噻二唑）成功地将共聚物的光学带隙从 2.31 eV（HMPBDT）降低到 1.78 eV（PBDT-BT）。通过将这些结构相关的聚合物与 PCBM 共混来制备体异质结光伏器件，以研究其光电性能。优化后的 HMPBDT:PCBM（1:3，180nm）器件的开路电压（Voc）提高到 0.76V，短路电流密度（Jsc）为 0.34mA/cm2，填充因子（FF）为 0.40，光电转换效率（PCE）为 0.10%。原子力显微镜（AFM）观察到薄膜的大相分离和大带隙是电流小的原因。优化后的 PBDT-BT:PCBM（1:3，55nm）器件的光电转换效率提高到 0.6%，Voc 为 0.72V，Jsc 为 2.06mA/cm2，FF 为 0.42。电流的显著提高归因于较低的带隙和更好的薄膜形貌。然而，低空穴迁移率限制了 PBDT-BT:PCBM 薄膜的厚度，无法使用更厚的薄膜，这将利用更多的光并提高电流。如果通过新材料设计，结合低带隙和低 HOMO 能级，进一步改善空穴迁移率和薄膜形貌，则有望进一步提高性能。
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