Highly Efficient and Reproducible Nonfullerene Solar Cells from Hydrocarbon Solvents

Abstract

With chlorinated solvents unlikely to be permitted for use in solution-processed organic solar cells in industry, there must be a focus on developing non-chlorinated solvent systems. Here we report high efficiency devices utilising a low-bandgap donor polymer (PffBT4T-2DT) and a nonfullerene acceptor (EH-IDTBR), from hydrocarbon solvents and without using additives. When mesitylene was used as the solvent, rather than chlorobenzene, an improved power conversion efficiency (11.1%) was achieved without the need for pre-or post-treatments. Despite altering the processing conditions to environmentally friendly solvents and room temperature coating, grazing incident X-ray measurements confirmed that active layers processed from hydrocarbon solvents retained the robust nano-morphology obtained with hot-processed chlorinated solvents. The main advantages of hydrocarbon solvent processed devices, besides the improved efficiencies, were the reproducibility and storage lifetime of devices. Mesitylene devices showed better reproducibility and shelf-life up to 4000h with PCE dropping by only 8% of its initial value.

A 3‐Fluoro‐4‐hexylthiophene‐Based Wide Bandgap Donor Polymer for 10.9% Efficiency Eco‐Friendly Nonfullerene Organic Solar Cells

“…However, the device processed by CB/DIO, its PCE dropped by 45% after 2 h of testing. It can be estimated that nonhalogenated solvents cause less damage to donor and acceptor materials in air with the light illumination because of the stable molecular structures of these solvents consisting of stable carbon and hydrogen atoms …”

Twist and Degrade—Impact of Molecular Structure on the Photostability of Nonfullerene Acceptors and Their Photovoltaic Blends

“…An inability to tune the chemical structure inhibits morphological or energetic optimization, to the effect that progress in the field has mostly been driven by the design Nonfullerene acceptors (NFAs) dominate organic photovoltaic (OPV) research due to their promising efficiencies and stabilities. [14,15] Accompanied by reports of good compatibility with nonchlorinated solvents [16] and low thickness-dependent performance, [17] NFAs provide encouraging potential for commercial scale-up. Here, the important role of molecular structure and conformation in NFA photostability in air is investigated by comparing structurally similar but conformationally different promising NFAs: planar O-IDTBR and nonplanar O-IDFBR.…”

Influence of Polymer Aggregation and Liquid Immiscibility on Morphology Tuning by Varying Composition in PffBT4T‐2DT/Nonfullerene Organic Solar Cells

“…It is thought that the temperature‐dependent aggregation (TDA) behavior of PffBT4T polymers is a key factor behind the favorable morphology in as‐cast devices, leading to the formation of highly pure polymer crystallites around 40 nm in size for a variety of processing parameters (e.g., spin speed, temperature, and concentration) and fullerenes . Blends of PffBT4T polymers (namely, PffBT4T‐2OD or its longer side‐chain derivative, PffBT4T‐2DT) with rhodanine‐flanked nonfullerene acceptors show comparable crystalline polymer domains, but offer several advantages over their fullerene counterparts, namely higher voltages, reduced voltage losses, improved stability toward thermal and burn‐in degradation, and also show enhancement in efficiency and shelf life when processed from hydrocarbon solvents . D/A ratio tuning and its impact on morphology in blends of the PffBT4T polymers with either fullerenes or NFAs is however not explored in detail …”