Suppressing Co‐Crystallization of Halogenated Non‐Fullerene Acceptors for Thermally Stable Ternary Solar Cells

Abstract

While photovoltaic blends based on non-fullerene acceptors are touted for their thermal stability, this type of acceptor tends to crystallize, which can result in a gradual decrease in photovoltaic performance and affects the reproducibility of the devices. Two halogenated indacenodithienothiophene-based acceptors that readily co-crystallize upon mixing are studied, which indicates that the use of an acceptor mixture alone does not guarantee the formation of a disordered mixture. The addition of the donor polymer to the acceptor mixture readily suppresses the crystallization, which results in a fine-grained ternary blend with nanometer-sized domains that do not coarsen due to a high T g ≈ 200 °C. As a result, annealing at temperatures of up to 170 °C does not markedly affect the photovoltaic performance of ternary devices, in contrast to binary devices that suffer from acceptor crystallization in the active layer. The results indicate that the ternary approach enables the use of high-temperature processing protocols, which are needed for upscaling and high-throughput fabrication of organic solar cells. Further, ternary devices display a stable photovoltaic performance at 130 °C for at least 205 h, which indicates that the use of acceptor mixtures allows to fabricate devices with excellent thermal stability.

Accelerating organic solar cell material's discovery: high-throughput screening and big data

“…57 Ternary OPV blends, which offer a series of long-term stability and performance advantages over the classical binary bulk heterojunctions, 71 have also been effectively screened by means of compositional libraries realized by blade coating. 27,72 In this case, a layer-by-layer strategy was employed to subsequently deposit, one on top of the other, the different layers of the constituent active layer materials. Depending on the layer ordering and velocity profile employed (either constant speed or acceleration), complementary areas of the ternary diagram are covered, so that less than 5 combinatorial samples are required to explore a significant fraction of the ternary phase diagram.…”

Unraveling the Mystery of Ternary Organic Solar Cells: A Review on the Influence of Third Component on Structure–Morphology–Performance Relationships

“…Here, we cite other reports where the optimized ternary blend showed reduced crystallinity compared with the binary configuration. [ 96,108,109 ]…”

“…Many studies have shown that the addition of a third component can circumvent this issue, leading to more optimal sized domains and improved morphological stability. [ 97,108,119–121 ]…”

“…Reproduced under the terms of the CC BY 4.0 license. [ 108 ] Copyright 2020, The Authors. Published by Wiley‐VCH.…”

“…Numerous reports have shown the ability of the third component to suppress this aggregation, producing a better lifetime and in some cases even better PCE. Hultmark et al [ 108 ] studied a PTB7‐Th:ITIC‐4F:ITIC‐4Cl ternary system. Thermal annealing has a lesser effect on coarsening of the ITIC‐4F:ITIC‐4Cl phase in the ternary system than in both binary systems.…”