Publication Title: Intrinsic Photoconductivity Spectral Dependence as a Tool for Prediction of Open-Circuit Voltage in Organic Solar Cells
Real-world applications of Moorfield products in science
Prediction of Open-Circuit Voltage in Solar Cells
Paper Abstract
Organic materials are known for their variety of molecules. Methods to predict the parameters of organic photovoltaic (OPV) cells are required to avoid the time- and resource-consuming processes of manufacturing and testing OPVs. Usually, the open-circuit voltage (Uoc) is estimated as the difference between the ionization energy level of the electron donor molecule (Id) and the electron affinity level of the electron acceptor molecule (EAa). Various measurement methods are used to determine the energy level values of pure materials, which, when combined with energy level shifts due to the donor:acceptor interactions, make these estimations less precise. In this work, photoconductivity measurements were applied to the donor:acceptor films. Near threshold energy, the electron can be directly transferred from the donor to the acceptor molecule. The obtained charge transfer energy (ECT) shows the difference between Id and EAa in the film. This difference was compared to the Uoc value of an OPV made of the same donor:acceptor combination. We show that this approach provides less scattered results and a higher correlation coefficient compared to the Uoc estimation using energy level values.
How Moorfield products helped:
The solar cells were made on ITO-covered glass substrates (Präzisions Glas and Optik GmbH, https://www.pgo-online.com/intl/ito.html (Accessed on 26 September 2023) 5 Ω/sq.). PEDOT:PSS (AL4083) was spin-coated with a speed of 2000 rpm, acceleration of 2000 rpm/s, and spinning time of 60. The substrates were dried on a hotplate for 15 min at 120 °C temperature. The studied materials were dissolved in chlorobenzene with a concentration of 8–10 mg/mL. Various electron donor:acceptor material combinations were prepared by mixing two solutions with a mass ratio of 1:1 to ensure that the film morphology was the same as in the photoconductivity measurement samples. The solutions were spin-coated in an argon atmosphere with a spinning speed of 1200 rpm, acceleration of 1200 rpm/s, and spinning time of 60 s. The obtained samples were dried on a hotplate for 15 min at 140 °C. A 1 nm thick LiF electron transport layer and 100 nm thick Al electrodes were deposited using a Moorfield Nanotechnology MiniLab LT090A-MX thermal evaporator in a Jacomex glovebox. The Al deposition rate was ~0.2 nm/s. The final structure of the OPV cells was ITO/PEDOT:PSS/donor:acceptor/LiF/Al.
Open Access publication details:
Grzibovskis, R., Polaks, A. and Vembris, A. (2023) ‘Intrinsic Photoconductivity Spectral Dependence as a Tool for Prediction of Open-Circuit Voltage in Organic Solar Cells’, Energies, 16(18), p. 6728. Available at: https://doi.org/10.3390/en16186728.