基于三元非富勒烯体系的高效有机太阳能电池

Dual non-fullerene acceptors based high efficiency ternary organic solar cells

有机材料的“窄吸收”特性制约了有机太阳能电池(OPVs)性能的进一步突破,二元体异质结薄膜难以实现对太阳能的有效宽光谱利用.三元OPVs在二元体系中引入吸收互补的第三组分,能够增强器件光吸收,实现光电转化效率的大幅提升.近年来,非富勒烯受体材料的飞速进展,多次刷新有机太阳能电池最高效率记录,丰富并扩展了三元受体材料的选择范围.本文以非富勒烯受体材料Y6作为第三组分材料,高效率非富勒烯太阳能电池PBDB-T-2F:IT-4F作为基础二元器件,研究并分析了以双非富勒烯材料为受体的三元有机太阳能电池工作机理.通过光电特性分析,发现Y6的引入不仅能够增强器件近红外区域的光吸收能力,而且能够有效抑制双分子复合,提高电荷取出率,从而提高器件能量转换效率.通过调节Y6在三元体系中的质量百分比,在Y6占比为20 wt%时,器件实现最高的能量转换效率12.48%,相比于基础二元器件(10.59%)实现了17.85%的性能提升.

Organic photovoltaics(OPVs)have been considered as one of the preliminary candidates for the thirdgeneration solar cells due to their particularly advantages,such as light-weight,low cost,solution processability and mechanical flexibility.In recent years,the power conversion efficiency(PCE)of OPVs has achieved remarkable progress with the development of non-fullerene acceptors(NFAs),which exhibit stronger capability of light absorption and stability than the fullerene acceptors.However,the narrow absorption properties of organic materials still restrict the further breakthrough of the performance of OPVs.It is difficult for the binary heterojunction films to realize the effective wide spectrum utilization of solar energy.Ternary strategy,which consists of one donor and two acceptors or two donors and one acceptor in a bulk-heterojunction,has proven to be an effective and facile way to enhance performances of OPVs.The emergence of new NFAs such as ITIC,IT-4F,Y6 etc.greatly increases the selectivity of acceptors in a ternary system.It is necessary to investigate the compatibility of latest NFA materials and corresponding ternary device performance.In this article,we report a new ternary OPV system with dual NFAs and a polymer donor.The excellent NFA material(Y6),which was first reported in 2019,is used as the third component.Different concentrations of Y6 are introduced into the binary system based on PBDB-T-2F:IT-4F.The compatibility between materials and device performances are investigated through absorption capability of blend films,AFM,water contact angle,GISAXS,and corresponding electrical properties of devices.The 12.48%PCE is achieved from ternary OPVs with PBDB-T:IT-4F as the active layers containing 20wt%Y6 in acceptors,resulting from the enhanced Jsc of 22.09 mA/cm2,Voc of 0.83 V and FF of 68.45%.The origin of the improvement of the ternary OPVs is summarized below.Firstly,an apparently complementary absorption spectrum is obtained through the introduction of Y6,which has a stronger photo harvesting capability in the spectral range from 750 to 950 nm than IT-4F,and higher short current density(Jsc)is observed in the ternary devices than in the binary device.Secondly,a rougher surface of the active layer is observed by increasing the Y6 concentration,which may result in an inferior exciton dissociation and charge transport process,the existence of larger-scaled crystal is proved by the GISAXS technology.Thirdly,the introduced Y6 can help to suppress the bimolecular recombination,which is in favor of the incremental device performance.Approximately 17.85%PCE improvement is obtained in comparison with PBDB-T-2F:IT-4F based binary OPVs.