Dr. Zewdneh Genene Profile

Dr. Zewdneh Genene

at Chalmers Univ of Technology

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Publications (2)

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Proceedings Article | 1 October 2023 Presentation + Paper

Photostability of Y-type electron acceptor molecules and related copolymer

Suraj Prasad, Cleber Marchiori, Zewdneh Genene, Leif K. Ericsson, Moyses Araujo, Ergang Wang, Ellen Moons

Proceedings Volume 12660, 1266002 (2023) https://doi.org/10.1117/12.2679517

KEYWORDS: Copolymers, Molecules, X-ray photoelectron spectroscopy, FT-IR spectroscopy, Photobleaching, Absorption spectrum, Spectroscopy, Organic photovoltaics

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The lifetime of organic solar cells critically depends on the photochemical stability of the materials. To shed light on the photostability of novel Y-series electron acceptors, we investigate the evolution of optical properties and composition during one-sun illumination in ambient atmosphere of thin films of the small-molecule acceptor Y5 and its copolymers PF5-Y5 and PYT. We employ UV-vis, Fourier-transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS), to assess changes in these properties as a function of illumination time. UV-Vis spectra show that PF5-Y5 undergoes rapid photobleaching, while the Y5 spectrum remains essentially unaffected even after 30 hours of exposure. The absorption spectrum of PYT, which contains a different co-mer than PF5-Y5, is only weakly affected. XPS C1s spectra of the PF5- Y5 film show a decreasing main peak and the development of a new component after 30 hours exposure, while the Y5 film surface composition remained intact. The photodegradation products of PF5-Y5 are characterized by the presence of new carbonyl groups, emerging as absorption bands in the FTIR spectra, while such spectral changes are absent for the Y5 film, indicating that Y5 is resistant to photooxidation, while PF5-Y5 undergoes photochemical reactions. The faster photodegradation of PF5-Y5 compared to Y5 and PYT raises the question about the role of the copolymer’s BDT moiety in the photooxidation. These new insights on the dependence of the photostability of acceptor molecules on their molecular structure are expected to contribute to the design of stable acceptor copolymers for organic solar cells with long operational lifetimes.

Proceedings Article | 30 May 2022 Presentation

Polymer acceptors with flexible spacers afford efficient and mechanically robust all-polymer solar cells

Ergang Wang, Zewdneh Genene

Proceedings Volume PC12149, PC121490I (2022) https://doi.org/10.1117/12.2622558

KEYWORDS: Polymers, Solar cells, Protactinium, Mechanical efficiency, Stretchable circuits, Photovoltaics, Molecules, Molecular electronics, Modulation, Electronics

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All polymer solar cells (all-PSCs), consisting of a binary blend of a polymer donor (PD) and a polymer acceptor (PA), possess important advantages including enhanced morphological stability, improved mechanical flexibility, and better compatibility with large-area roll-to-roll production over small molecule acceptor (SMA)-based PSCs. High efficiency and mechanical robustness are both crucial for the practical applications of all-PSCs in stretchable and wearable electronics. In this regard, we report a series of new polymer acceptors (PAs) by incorporating a flexible conjugation-break spacer (FCBS) to achieve highly efficient and mechanically robust all-PSCs. Incorporation of FCBS affords the effective modulation of the crystallinity and pre-aggregation of the PAs, and achieves the optimal blend morphology with polymer donor (PD), increasing both the photovoltaic and mechanical properties of all-PSCs. In particular, the all-PSC based on PYTS-0.3 as a PA incorporated with 30% FCBS and a PD (PBDB-T) demonstrates a high power conversion efficiency (PCE) of 14.68% and excellent mechanical stretchability with a crack onset strain (COS) of 21.64% and toughness of 3.86 MJ m–3, which is significantly superior to those of devices with the PA without the FCBS (PYTS-0.0, PCE = 13.01% and toughness = 2.70 MJ m–3). To date, this COS is the highest value reported for PSCs with PCEs of over 8% without any insulating additives. These results reveal that the introduction of FCBS into the conjugated backbone is a highly feasible strategy to simultaneously improve the PCE and stretchability of PSCs resulting in their reliable applications in stretchable electronics.

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