给-受型噻吩衍生物有机半导体新材料的合成及光伏性能研究

A principal approach to improve the performance of organic photovoltaic materials is to introduce an electron-accepting unit into the framework of organic semiconductor materials as a donor and construct a donor-acceptor structure. It can effectively lower the band gap of donor materials and their highest occupied molecular orbital (HOMO), giving rise to a broad absorption spectrum along with larger open circuit voltage of the solar cell devices. In this project, a novel series of thiophene derivatives as new materials are designed and synthesized using a cyclopentadithiophene (or silylene-bithiophene, dithienopyrrole, benzodithiophene) electron-donating unit as a molecular core, hexylthiophen-2-thienyl as an electron-donating end-capping unit, and dibenzothiophene-S,S-dioxide-3,3΄-diyl as a new kind of electron-accepting embed unit or dibenzothiophene as an electron-donating embed unit. The physical and chemical properties of the thiophene derivatives, such as chemical structure, photo-physical, electrochemical, conductivity, are characterized, and the regulation mechanism for the introduction of the electron-accepting unit of dibenzothiophene-S,S-dioxide-3,3΄-diyl and the formation of donor-acceptor structure on their band gaps, energy levels and carrier mobility is discussed. Bulk heterojunction (BHJ) solar cells are fabricated utilizing the newly synthesized thiophene derivatives as donor materials, and the photovoltaic performances are studied so as to explore highly efficient donor-acceptor thiophene derivatives as potential photovoltaic materials, and disclose the intrinsic relationship between the molecular structure and the photovoltaic performance. The investigation can provide a reference for the molecular design of organic photovoltaic materials.

在有机半导体给体材料的分子骨架中嵌入受电子单元并构筑给-受结构是制备高性能光伏材料的主要途径。该结构可有效降低给体材料的带隙以拓宽其吸收光谱，降低其最高占据分子轨道（HOMO）能级以提高其有机太阳能电池的开路电压。本项目拟合成一系列以环戊二烯并双噻吩（或硅桥联二噻吩、二噻吩并吡咯、苯并二噻吩）给电子单元为分子中心，以己基联二噻吩基为端基给电子单元，中间被嵌入二苯并噻吩-S,S-二氧化物新型受电子单元或二苯并噻吩给电子单元的噻吩衍生物新材料；表征噻吩衍生物的化学结构、光物理、电化学和导电性等理化性能，揭示二苯并噻吩-S,S-二氧化物受电子单元的嵌入及给-受结构的构筑对其带隙、能级和载流子迁移率的调控机制；以新合成噻吩衍生物为给体材料制备本体异质结太阳能电池并研究其光伏性能，探索高效的给-受型噻吩衍生物光伏材料体系，并最终揭示出分子结构与光伏性能间的内在联系，为有机光伏材料的分子设计提供参考。

二苯并噻吩是一个平面型给电子单元，如果将其噻吩单元上的硫原子氧化，可使其转变为二苯并噻吩-S,S-二氧化物受电子单元，二苯并噻吩-S,S-二氧化物受电子单元是一个可用于构筑给-受型噻吩衍生物新材料的潜在官能团。本研究以二苯并噻吩-S,S-二氧化物为受电子单元、以苯并二噻吩（二噻吩并吡咯或硅桥联二噻吩）为给电子单元分子中心、以己基联二噻吩/己基苯基噻吩为端基给电子单元，设计合成了五种具有给-受结构的噻吩衍生物新材料；运用核磁共振谱（NMR）、质谱（MS）和红外光谱（FT-IR）等分析方法确认了噻吩衍生物新材料的化学结构。采用紫外吸收光谱（UV-vis）和荧光发射（PL）光谱表征了噻吩衍生物的光物理性能，并根据UV-vis的吸收波边测算了噻吩衍生物的光学带隙。噻吩衍生物在薄膜中的UV-vis和PL光谱相对与其在溶液中的光谱具有明显的偏移和宽化，表明噻吩衍生物分子在固态薄膜中可紧密堆积并存在一定程度的分子间π-π相互作用。采用循环伏安法（CV）测算了噻吩衍生物新材料的HOMO（最高占据分子轨道）能级，结果表明噻吩衍生物均具有较低的HOMO能级。分析了二苯并噻吩-S,S-二氧化物受电子单元、共轭链长度和其它给电子单元对噻吩衍生物材料带隙及能级的影响规律。采用溶液旋涂法制备了以噻吩衍生物为活性层的“顶接触型”薄膜场效应三极管，器件的输出特性表明所合成的噻吩衍生物为P-型有机半导体材料。以噻吩衍生物为给体材料，以商品化的富勒烯衍生物（PC61BM）为受体材料，采用溶液旋涂法制备了本体异质结有机太阳能电池器件。结果表明：噻吩衍生物较低的HOMO能级可赋予电池器件较高的开路电压（0.68-0.84 V），但电池器件的能量转换效率较低、尚有很大的提升空间。