Comparing and Quantifying Indoor Performance of Organic Solar Cells

Dana Lübke^a, Paula Hartnagel^a, Johanna Angona^a, Thomas Kirchartz^a^,^b

^aIEK-5 Photovoltaik, Forschungszentrum Jülich GmbH, Germany, 52425 Jülich, Germany

^bUniversity of Duisburg-Essen and CENIDE, Faculty of Engineering, Duisburg, Germany

International Conference on Hybrid and Organic Photovoltaics
Proceedings of 13th Conference on Hybrid and Organic Photovoltaics (HOPV21)

Online, Spain, 2021 May 24th - 28th

Organizers: Marina Freitag, Feng Gao and Sam Stranks

Oral, Dana Lübke, presentation 048
Publication date: 11th May 2021

With the development of a broad range of strongly absorbing non-fullerene absorbers in the last five years, the power conversion efficiencies of organic solar cells have increased rapidly and are now approaching 20% [1],[2]. The market of the internet of things is emerging remarkably and demands to drive high amounts of off-grid low power consumption devices [3],[4]. The possibility to produce solution-based, low-cost and flexible solar foils makes OPV (organic photovoltaics) a good candidate to fulfil this demand.

Although efficiencies for iOPV (indoor OPV) have improved substantially [5]–[9], it is hard to determine champion solar cells due to a lack of standardized comparison methods [4],[10],[11]. Different authors use different conditions to evaluate the performance of devices. The set-ups differ in the source of light with varying color temperatures and intensities. The overlap of the materials’ absorption spectra and the spectral emission power of the light-source defines the short circuit current density [12]. Consequently, the performance depends on the intensity and color temperature of the light-source, which makes the comparability between publications difficult. Furthermore, the intensity of the emission power determines the input power and therefore the efficiency as well.

To address the problem of unavoidable arbitrariness of light-sources one needs to find figures of merit, which are easy to use by the OPV community. In this meta-analysis, we present an evaluation method based on the measurement of the external quantum efficiency combined with relative measurements of the spectral irradiance and current-voltage characteristics at different light intensities with one light-source. This set of experimental data, enables us to calculate the efficiency of organic solar cells under the illumination of several different light-sources and intensities which now allows cross-publication between published or in house data.

We investigate the dependence of the efficiency of the solar cells on the spectra of the light-sources and found the efficiency to deviate ~20 % as a function of the color temperature of the LED. As our approach ensures equal evaluation conditions, we present a meta-analysis of organic solar cells for indoor applications and compare the state of the art with thermodynamic efficiency limits under indoor illumination. We find that the optimal bandgap of the absorber material depends on the used light-source and ranges between 1.75 eV and 2 eV. The presented calculation is unique in literature and a powerful tool to detect possible candidates for high indoor performance solar cells.

References:

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[5] Lee, H.K.H., Wu, J., Barbé, J., Jain, S.M., Wood, S., Speller, E.M., Li, Z., Castro, F.A., Durrant, J.R., and Tsoi, W.C., Organic photovoltaic cells – promising indoor light harvesters for self-sustainable electronics. J. Mater. Chem. A 2018, 6 (14), 5618–5626.

[6] Xu, Y., Yao, H., Ma, L., Wu, Z., Cui, Y., Hong, L., Zu, Y., Wang, J., Woo, H.Y., and Hou, J., Organic photovoltaic cells with high efficiencies for both indoor and outdoor applications. Mater. Chem. Front. 2021, 5 (2), 893–900.

[7] Cui, Y., Wang, Y., Bergqvist, J., Yao, H., Xu, Y., Gao, B., Yang, C., Zhang, S., Inganäs, O., Gao, F., and Hou, J., Wide-gap non-fullerene acceptor enabling high-performance organic photovoltaic cells for indoor applications. Nat. Energy 2019, 4 (9), 768–775.

[8] Cui, Y., Yao, H., Zhang, T., Hong, L., Gao, B., Xian, K., Qin, J., and Hou, J.,1 cm-2 Organic Photovoltaic Cells for Indoor Application with over 20% Efficiency. Adv. Mater. 2019, 31 (42), 1904512.

[9] Ma, L.K., Chen, Y., Chow, P.C.Y.Y., Zhang, G., Huang, J., Ma, C., Zhang, J., Yin, H., Hong Cheung, A.M., Wong, K.S., So, S.K., Yan, H., Man, A., Cheung, H., Wong, K.S., Kong, S., Ma, C., Zhang, J., Yin, H., Hong Cheung, A.M., Wong, K.S., So, S.K., and Yan, H., High-Efficiency Indoor Organic Photovoltaics with a Band-Aligned Interlayer. Joule 2020, 4 (7), 1486–1500.

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[11] Virtuani, A., Lotter, E., and Powalla, M., Influence of the light source on the low-irradiance performance of Cu(In,Ga)Se2 solar cells. Sol. Energy Mater. Sol. Cells 2006, 90 (14), 2141–2149.

[12] Cui, Y., Hong, L., and Hou, J., Organic Photovoltaic Cells for Indoor Applications: Opportunities and Challenges. ACS Appl. Mater. Interfaces 2020, 12 (35), 38815–38828.

Acknowledgements:

We acknowledge funding from the state of Nordrhein-Westfalen via the project Enerscale and funding from the Helmholtz Association. The authors declare no competing interest.

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