D-π-A型共轭聚合物的合成及其光伏性能

Synthesis and Photovoltaic Properties of D-π-A Type Conjugated Polymers

设计合成了3种主链相同、侧基不同的Donor(D)-π-Acceptor(A)型共轭聚合物:聚[(4,8-二辛氧基苯[1,2-b;3,4-b]二噻吩)-(9-(4-氰基苯基)-9H-咔唑)](PBDTCz-CN)、聚[(4,8-二辛氧基苯[1,2-b;3,4-b′]二噻吩)-(9-(4-醛基苯基)-9H-咔唑)](PBDTCz-CHO)和聚[(4,8-二辛氧基苯[1,2-b;3,4-b]二噻吩)-(9-(4-硝基苯基)-9H-咔唑)](PBDTCz-NO_2)。通过调变侧基上的受体基团,比较了氰基、醛基、硝基对聚合物光学和电学性能的影响,讨论了影响聚合物光电转换效率的主要因素。3种聚合物的光学带隙和线性吸收系数依次分别为2.32 eV,152.0 L/(g·cm);2.43 eV,58.5 L/(g·cm)和2.25 eV,85.5 L/(g·cm)。在这些聚合物中,彼此间的最高占据分子轨道(HOMO)能级差距很小,PBDTCz-NO_2的最低未占据分子轨道(LUMO)能级最低(-3.38eV)。在100 W/m^2模拟太阳光的照射下,基于这些聚合物的光伏器件(器件结构:ITO/PEDOT:PSS/Polymer:[70]PCBM(1:2)/Ca/A1)的光电转换效率分别为0.44%(PBDTCz-CN)、0.001 8%(PBDTCz-CHO)和0.23%(PBDTCz-NO_2)。低的光电转换效率主要归因于低的短路电流,而影响短路电流的主要原因有自身吸光性能的限制和弱的π-π堆砌作用。

A series of D-π-A type conjugated polymers with the same polymer backbone and different side chains, including poly[（4,8-bis（octyloxy）benzo[1,2-b;3,4-b′]dithiophene）-（4-（9H-carbazol-9-yl）benzonitrile）] （PBDTCz-CN）, poly[（4,8-bis（octyloxy）benzo[1,2-b;3,4-b′]dithiophene）-（4-（9H-carbazol-9-yl）benzaldehyde）] （PBDTCz-CHO）, and poly[（4,8-bis（octyloxy）benzo[1,2-b;3,4-b′]dithiophene）-（9-（4-nitrophenyl）-9H-carbazole）] （PBDTCz-NO2）, were designed and synthesized. By replacing the electron-deficient group in the side chain, it resulted in significant changes to the optical and electrochemical properties of the polymers, as well as the subsequent performances of devices made from these materials. The optical bandgap and absorption coefficient of these polymers are 2.32 eV and 152.0 L/（g·cm） for PBDTCz-CN; 2.43 eV and 58.5 L/（g·cm） for PBDTCz-CHO; 2.25 eV and 85.5 L/（g·cm） for PBDTCz-NO2. Among these polymers, the energy differences between the HOMO level of each polymer are very small. PBDTCz-NO2 shows the lowest LUMO energy level of -3.38 eV. Photovoltaic properties of these polymers were investigated initially with a bulk heterojunction （BHJ） device configuration of ITO/PEDOT∶PSS/Polymer∶[70]PCBM （1∶2）/Ca/Al under the illumination of AM 1.5G at 100 W/cm. The obtained power conversion efficiencies are 0.44% for PBDTCz-CN, 0.001 8% for PBDTCz-CHO and 0.23% for PBDTCz-NO2, respectively. The low short-circuit current density is assigned to the limited absorption and poor π-π stacking interactions between polymer chains.