Uncovering the out-of-plane nanomorphology of organic photovoltaic bulk heterojunction by GTSAXS

Xinxin Xia,Pok Fung Chan,Na Li,Gang Li,Tao Zhu,Xuyun Guo,Guilong Cai,Haiming Zhu,Zeng Chen,Heng Liu,Ye Zhu,Yuhao Li,Xiaowei Zhan,Xun-Li Wang,Xu Lian ,Minchao Qin,Xiaozhi Zhan,Yiqun Xiao,Kuan Liu,Tsz‐Ki Lau ,Xinhui Lu

doi:10.1038/s41467-021-26510-6

Abstract

The bulk morphology of the active layer of organic solar cells (OSCs) is known to be crucial to the device performance. The thin film device structure breaks the symmetry into the in-plane direction and out-of-plane direction with respect to the substrate, leading to an intrinsic anisotropy in the bulk morphology. However, the characterization of out-of-plane nanomorphology within the active layer remains a grand challenge. Here, we utilized an X-ray scattering technique, Grazing-incident Transmission Small-angle X-ray Scattering (GTSAXS), to uncover this new morphology dimension. This technique was implemented on the model systems based on fullerene derivative (P3HT:PC71BM) and non-fullerene systems (PBDBT:ITIC, PM6:Y6), which demonstrated the successful extraction of the quantitative out-of-plane acceptor domain size of OSC systems. The detected in-plane and out-of-plane domain sizes show strong correlations with the device performance, particularly in terms of exciton dissociation and charge transfer. With the help of GTSAXS, one could obtain a more fundamental perception about the three-dimensional nanomorphology and new angles for morphology control strategies towards highly efficient photovoltaic devices.

Highlights

The bulk morphology of the active layer of organic solar cells (OSCs) is known to be crucial to the device performance
RSoXS collects the signal transmitted through the backside of the thin film sample, but Grazing-incident Transmission Small-angle X-ray Scattering (GTSAXS) collects the signal exited from the front edge by aligning the cleaved front edge of the thin film sample at the center of the goniometer stage (Supplementary Fig. 1, details in method section)
Having demonstrated the capability of GTSAXS in the prototypical fullerene-based system, we extend this method to NF systems and investigate the influence of OOP nanomorphology on the device performance

Summary

Introduction

The bulk morphology of the active layer of organic solar cells (OSCs) is known to be crucial to the device performance. We utilized an X-ray scattering technique, Grazing-incident Transmission Small-angle X-ray Scattering (GTSAXS), to uncover this new morphology dimension This technique was implemented on the model systems based on fullerene derivative (P3HT:PC71BM) and non-fullerene systems (PBDBT:ITIC, PM6:Y6), which demonstrated the successful extraction of the quantitative out-of-plane acceptor domain size of OSC systems. To reveal the OOP nanomorphology of organic BHJ active layers, an X-ray scattering technique called grazingincident transmission small-angle X-ray scattering (GTSAXS) was employed[21]. This technique allows the detection of scattering under the surface horizon of the film which, unlike GISAXS, could be modeled readily using modified simple Born approximation[10]. The proposed analysis scheme can be readily migrated to study the inner 3D nanostructure of other functional thin film systems beyond OPV, such as polymer materials, nanofiltration membranes, quantum dot, and perovskite thin films

Methods

Results

Conclusion