Control of aggregated structure of photovoltaic polymers for high‐efficiency solar cells

Abstract

π-Conjugated organic/polymer materials-based solar cells have attracted tremendous research interest in the fields of chemistry, physics, materials science, and energy science. To date, the best-performance polymer solar cells (PSCs) have achieved power conversion efficiencies exceeding 18%, mostly driven by the molecular design and device structure optimization of the photovoltaic materials. This review article provides a comprehensive overview of the key advances and current status in aggregated structure research of PSCs. Here, we start by providing a brief tutorial on the aggregated structure of photovoltaic polymers. The characteristic parameters at different length scales and the associated characterization techniques are overviewed. Subsequently, a variety of effective strategies to control the aggregated structure of photovoltaic polymers are discussed for polymer:fullerene solar cells and polymer:nonfullerene small molecule solar cells. Particularly, the control strategies for achieving record efficiencies in each type of PSCs are highlighted. More importantly, the in-depth structure-performance relationships are demonstrated with selected examples. Finally, future challenges and research prospects on understanding and optimizing the aggregated structure of photovoltaic polymers and their blends are provided.

Morphology control in high‐efficiency all‐polymer solar cells

“…• Understanding the synergistic effects of key morphology control methods At present, solvent engineering, additive engineering, thermal annealing, and solvent vapor annealing can effectively optimize the morphology of the blend films. 151 The method that works for one system is not necessarily effective for another system. Thus, these optimization methods often need to be carefully and even fully explored.…”

“…At present, solvent engineering, additive engineering, thermal annealing, and solvent vapor annealing can effectively optimize the morphology of the blend films 151 . The method that works for one system is not necessarily effective for another system.…”

Eco‐friendly solution processing of all‐polymer solar cells: Recent advances and future perspective

“…More requirements should be taken into consideration, including solution processability and toxicity, film thickness tolerance, morphological evolution, and post-treatment for printing deposition. 91,92 As the morphology of blend films highly depends on the processing conditions, a better understanding of the blend film evolution mechanism by printing methods is essential for the large-scale fabrication of high-efficiency eco-friendly all-PSCs. Some all-PSC cases have attempted to optimize morphology and performance by printing deposition methods, such as blade coating, slot-die coating, screening printing, and inkjet printing.…”

“…The much slower solidification provides a long time to aggregate and crystallize, which can lead to the formation of oversized domain or excessive phase separation in the films, especially for the currently reported high‐performance non‐fullerene acceptors with high crystallinity and aggregation features. More requirements should be taken into consideration, including solution processability and toxicity, film thickness tolerance, morphological evolution, and post‐treatment for printing deposition 91,92 . As the morphology of blend films highly depends on the processing conditions, a better understanding of the blend film evolution mechanism by printing methods is essential for the large‐scale fabrication of high‐efficiency eco‐friendly all‐PSCs.…”

Phenalene—A New Ring-Locked Vinyl Bridge for Nonfullerene Acceptors With Enhanced Chemical and Photochemical Stabilities

“…As one of the third-generation photovoltaic techniques, organic solar cells (OSCs) have demonstrated outstanding potentials in the fields of flexible devices, semi-transparent devices, indoor photovoltaics, and so on (Liu et al, 2021c;Dauzon et al, 2021;Kini et al, 2021;Xie et al, 2021). Excitingly, the record power conversion efficiency (PCE) of OSCs has been continuously rising in recent years, and a value exceeding 19% has been achieved already Wang et al, 2021), attributed to the innovative design and exploitation of photovoltaic materials and device architecture (Li et al, 2019;Cui and Li, 2021;Liu W. et al, 2021;Gao et al, 2021;Ren et al, 2021;Yin et al, 2021;Zheng et al, 2021). In particular, A-D-A-type nonfullerene acceptors (NFAs) play the most critical role in achieving high-performance OSCs since the emergence of the representative NFA molecule, namely ITIC, reported by Zhan et al, in 2015(Lin et al, 2015, where "D" and "A" represent the electron-donating and electron-accepting units, respectively.…”