Chang Chun-Yu, Huang Yu-Ching, Tsao Cheng-Si, Chen Chien-An, Su Chun-Jen, Su Wei-Fang
Department of Materials Science and Engineering, National Taiwan University, Taipei 10617, Taiwan.
Institute of Nuclear Energy Research, Taoyuan 32546, Taiwan.
Phys Chem Chem Phys. 2017 Aug 30;19(34):23515-23523. doi: 10.1039/c7cp04238h.
The high power conversion efficiency of bulk heterojunction (BHJ) polymer solar cells can be achieved from either low crystallinity (P3TI) or high crystallinity (P6TI) of isoindigo-based donor-acceptor alternating copolymers blended with PCBM by controlling nanophase separation using additives. P3TI shows similar device performance regardless of the type of additives, while P6TI is significantly affected by whether the additive is aliphatic or aromatic. To understand the interplays of crystallinity of polymers and the type of additive on the formation of nanomorphology of BHJ, we employed the simultaneous grazing-incidence small- and wide-angle X-ray scattering (GISAXS and GIWAXS) technique to perform the quantitative investigation. By incorporating additives, the PCBM molecules can be easily intercalated into the P3TI polymer-rich domain and the size of the PCBM clusters is reduced from about 24 nm to about 5 nm by either aliphatic 1,8-diiodooctane (DIO) or aromatic 1-chloronaphthalene (CN). On comparison, it is found to be more difficult for PCBM molecules to be intercalated into the highly crystalline P6TI dense domain, and the PCBM molecules have a higher tendency to be self-aggregated, which results in a larger size of PCBM clusters of about 58 nm. The clusters can be reduced to about 7 nm by DIO and 13 nm by CN. The presence of crystallites in the P6TI domain can interact with the additive to tailor the crystallization of PCBM clusters to a size similar to that of P6TI crystallites (∼12 nm) and form a connected network for efficient charge transportation. Thus, the power conversion efficiency of P6TI:PCBM reaches its maximum of 7.04% using aromatic CN additives. This is a new finding of the effect of crystallinity, which is not observed in the common low crystalline donor-acceptor alternating copolymers such as PTB7. Our results provide a useful guideline to manipulate the desired morphology of BHJ films constructed from alternating copolymer with different crystallinity, which is critical for achieving high power conversion efficiency of solar cells.
通过使用添加剂控制纳米相分离，基于异吲哚的供体-受体交替共聚物与PCBM混合时，无论是低结晶度（P3TI）还是高结晶度（P6TI），均可实现体异质结（BHJ）聚合物太阳能电池的高功率转换效率。无论添加剂类型如何，P3TI均表现出相似的器件性能，而P6TI则受添加剂是脂肪族还是芳香族的显著影响。为了理解聚合物结晶度与添加剂类型对BHJ纳米形态形成的相互作用，我们采用同步掠入射小角和广角X射线散射（GISAXS和GIWAXS）技术进行定量研究。通过加入添加剂，PCBM分子可轻松插入富含P3TI聚合物的区域，脂肪族的1,8-二碘辛烷（DIO）或芳香族的1-氯萘（CN）均可将PCBM团簇的尺寸从约24 nm减小至约5 nm。相比之下，发现PCBM分子更难插入高结晶度的P6TI致密区域，且PCBM分子具有更高的自聚集倾向，这导致PCBM团簇尺寸更大，约为58 nm。DIO可将团簇尺寸减小至约7 nm，CN可将其减小至13 nm。P6TI区域中微晶的存在可与添加剂相互作用，将PCBM团簇的结晶调整至与P6TI微晶（~12 nm）相似的尺寸，并形成用于高效电荷传输的连通网络。因此，使用芳香族CN添加剂时，P6TI:PCBM的功率转换效率最高可达7.04%。这是结晶度影响方面的一项新发现，在常见的低结晶度供体-受体交替共聚物（如PTB7）中未观察到。我们的结果为操控由不同结晶度的交替共聚物构建的BHJ薄膜的理想形态提供了有用的指导方针，这对于实现太阳能电池的高功率转换效率至关重要。
