Garcia Romero David, Di Mario Lorenzo, Portale Giuseppe, Loi Maria Antonietta
Zernike Institute for Advanced Materials, University of Groningen Nijenborgh 4 Groningen 9747 AG The Netherlands
J Mater Chem A Mater. 2021 Oct 11;9(42):23783-23792. doi: 10.1039/d1ta08232a. eCollection 2021 Nov 2.
The control of morphology and microstructure during and after the active layer processing of bulk-heterojunction solar cells is critical to obtain elevated fill factors and overall good device performance. With the recent development of non-fullerene acceptors, wide attention has been paid to improve miscibility, solubility and nanoscale separation by laborious molecular design processes and by the use of additives. Nonetheless, several post-processing strategies can equally contribute to obtain an optimum phase separation and even to an enhanced crystallinity, but their effect on performance and device lifetime of polymer/non-fullerene acceptor solar cells is still unclear. Herein, we report a systematic comparison between different post-processing treatments including thermal annealing (TA), vacuum drying (VD) and solvent vapor annealing (SVA) on the TPD-3F polymer and IT-4F non-fullerene acceptor, comparing their effects on device performance as well as on the morphology and optical and electrical properties. The optimized SVA treated devices exhibited power conversion efficiencies close to 14% with a remarkable 76% fill factor and superior short-circuit currents compared to the one of untreated devices. Moreover, SVA demonstrated improvements in device stability both under illumination and under ambient conditions. The induced phase separation and the increased crystallinity of the acceptor molecules, as revealed by GIWAXS measurements, led to increased photogenerated currents, with a more effective exciton dissociation and charge collection. The open-circuit voltage losses in the SVA and TA devices were explained by a bandgap reduction and a higher trap-assisted recombination, respectively. Overall, our study points to the role of post-processing in organic solar cell fabrication, and contributes towards a new generation of efficient and stable additive-free organic solar cells.
在体异质结太阳能电池活性层处理期间及之后对其形态和微观结构进行控制，对于获得较高的填充因子和整体良好的器件性能至关重要。随着非富勒烯受体的最新发展，人们通过繁琐的分子设计过程以及使用添加剂，在改善混溶性、溶解性和纳米级分离方面给予了广泛关注。尽管如此，几种后处理策略同样有助于实现最佳的相分离，甚至提高结晶度，但其对聚合物/非富勒烯受体太阳能电池性能和器件寿命的影响仍不明确。在此，我们报告了对TPD - 3F聚合物和IT - 4F非富勒烯受体进行不同后处理（包括热退火（TA）、真空干燥（VD）和溶剂气相退火（SVA））之间的系统比较，比较它们对器件性能以及形态、光学和电学性质的影响。与未处理的器件相比，经过优化的SVA处理的器件表现出接近14%的功率转换效率、显著的76%的填充因子以及优异的短路电流。此外，SVA在光照和环境条件下均显示出器件稳定性的提高。GIWAXS测量结果表明，受体分子诱导的相分离和结晶度增加导致光生电流增加，激子解离和电荷收集更有效。SVA和TA器件中的开路电压损失分别由带隙减小和更高的陷阱辅助复合来解释。总体而言，我们的研究指出了后处理在有机太阳能电池制造中的作用，并有助于新一代高效且无添加剂的稳定有机太阳能电池的发展。
