Low band gap conjugated small molecules containing benzobisthiadiazole and thienothiadiazole central units: synthesis and application for bulk heterojunction solar cells
作者:J. A. Mikroyannidis、D. V. Tsagkournos、S. S. Sharma、Y. K. Vijay、G. D. Sharma
DOI:10.1039/c0jm03436c
日期:——
Two novel conjugated low band gap small molecules (SMs), M1 and M2, containing benzobisthiadiazole and thienothiadiazole central units, respectively, were synthesized. Both SMs carried terminal cyanovinylene 4-nitrophenyl at both sides which were connected to the central unit with a thiophene ring. The long-wavelength absorption band was located at 591–643 nm and the optical band gap was 1.62–1.63 eV, which is lower than that of P3HT. These two SMs were investigated as electron donor materials along with PCBM or F as electron acceptors for fabrication of bulk heterojunction (BHJ) organic photovoltaic devices. F is a modified PCBM which has been previously synthesized and used as an electron acceptor for poly(3-hexylthiophene) (P3HT). The power conversion efficiency (PCE) for M1:PCBM, M1:F, M2:PCBM and M2:F was 1.05%, 2.02%, 1.23% and 2.72%, respectively. The higher PCE for the devices with M2 as the electron donor has been related to the improved hole mobility for M2. However, the improved PCE for the devices with F as the electron acceptor has been attributed to the more intense absorption of F in the visible region than that of PCBM and also to the higher open circuit voltage resulting from the higher LUMO level of F. We have also fabricated devices with M2:F cast film from mixed solvents. The PCE for the BHJ devices with the as cast and thermally annealed M2:F (mixed solvents) is 3.34% and 3.65%, respectively.
合成了两种新型低带隙共轭小分子(SMs),M1和M2,分别含有苯并双噻二唑和噻吩并噻二唑中心单元。两者均在两侧携带有氰基乙烯基的4-硝基苯,通过噻吩环与中心单元相连。长波长吸收带位于591-643 nm处,光学带隙为1.62-1.63 eV,低于P3HT的带隙。这两种小分子与PCBM或F作为电子受体一起被研究,用于制备体异质结(BHJ)有机光伏器件。F是一种改良的PCBM,之前已被合成并作为电子受体用于聚(3-己基噻吩)(P3HT)。M1:PCBM、M1:F、M2:PCBM和M2:F的功率转换效率(PCE)分别为1.05%、2.02%、1.23%和2.72%。M2作为电子给体的器件具有较高的PCE,归因于M2的空穴迁移率提高。然而,以F作为电子受体的器件PCE提高归因于F在可见区域的吸收比PCBM更强,以及由于F的LUMO能级较高导致的开路电压更高。我们还制备了从混合溶剂中浇铸的M2:F薄膜器件。BHJ器件中未经热退火和经过热退火的M2:F(混合溶剂)的PCE分别为3.34%和3.65%。