(Invited) High Performance Ternary Organic Solar Cells Based on Non-Fullerene Acceptors
Authors: Torimtubun Alfonsina Abat Amelenan , Sanchez Jose Guadalupe , Ferre-Borrull Josep , Marsal Lluis F. 
Published: July 2021

Organic solar cells (OSCs) comprising of a photoactive layer of electron-donor and electron-acceptor have attracted great attention for decades due to their low-cost, large-area, solution-processed in flexible substrates, and indoor light energy harvester [1,2]. Their power conversion efficiencies (PCEs) have been boosted to over 18% via material design, device engineering, and theoretical studies [3]. One of the most promising methods to improve device performance is adding a third component into a binary system, resulting in a ternary blend. Ternary blends can form an even larger variety of morphologies, depending on the ratio and the interactions between the components. In a ternary blend, the third components not only provide a broadened light harvesting and optimizing the film morphology, but also facilitating exciton dissociation and charge transport. As a consequence, it is improving the device performance of OSCs, i.e., the fill factor (FF), short-circuit current density (Jsc), open-circuit voltage (Voc) and power conversion efficiency (PCE). On the other hand, the rapid progress of highly efficient NFAs materials has offered a new opportunity for studying ternary OSCs due to the great tunability of chemical structures, optical properties and electronic properties of NFAs, and their ability to phase separate into nanoscopic domains in blended thin films [4].
In this study, we have been focusing first on the optimization of binary systems using fullerene and non-fullerene acceptors. We performed several strategies to improve the device performance and stability of these binary systems: engineering the electron transport layers, annealing treatment, using inkjet printing and spray pyrolysis deposition methods, and photoactive materials engineering. As a result, we achieved PCEs from ~3% using P3HT as donor polymer, ~10% PCE using PTB7-Th donor polymer up to more than 17% efficiency using PM6 donor polymer [5–10]. To the next level, we shift the direction of our work using ternary system through careful selection of the third component in donor-acceptor materials. However, blending three light-absorbing semiconductor materials is not a trivial work. A huge materials combination, their compatibility, relative-energies of their frontier orbitals and solubility need to be considered to achieve a successful high performance ternary bulk heterojunction OSCs.
To date, we have been able to improve device performance by using new phthalocyanines derivatives as third components in binary PTB7-Th:PC70BM due to their high extinction coefficients, stability, and energy band gaps well-matched to the incident solar spectrum [11]. The proper choice of the central atom in pthalocyanine compound were studied to know their effect to the electrical parameters and absorption spectra of OSCs. Moreover, we also compare the effect of fullerene PC70BM and non-fullerene ITIC-M as third components in the bulk heterojunctions of PM6:Y7-based devices.

Acknowledgements: This work was supported by the Ministerio de Ciencia, Innovación y Universidades (MICINN/FEDER) RTI2018-094040-B-I00, by the Agency for Management of University and Research Grants ref. 2017-SGR-1527 and by the Catalan Institution for Research and Advanced Studies (ICREA) under the ICREA Academia Award

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