Light intensity dependence of External Quantum Efficiency of fresh and degraded organic photovoltaics

• Published in: Solar energy materials and solar cells Vol. 144; pp. 273 - 280
• Main Authors: Katz, E.A., Mescheloff, A., Visoly-Fisher, I., Galagan, Y.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-01-2016
• Subjects: Current collection; Degradation; Devices; External Quantum Efficiency; Incident light; Luminous intensity; Organic photovoltaics; Photovoltaic cells; Quantum efficiency; Solar cells; Traps; Degradation; Traps; Organic photovoltaics; Current collection; External Quantum Efficiency
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2015.09.020

The effect of light intensity on the External Quantum Efficiency (EQE) of encapsulated bulk heterojunction organic photovoltaics (OPV) is presented. The measurements were applied to devices based on poly(3-hexylthiophene) (P3HT) blended with the fullerene derivative phenylC61-butyric acid methyl ester (PCBM) in as-produced and various degradation states. The degradation of current collection in the OPV devices is shown to enhance the sub-linear dependence of the short-circuit current on light intensity, and the corresponding EQE decrease with increasing incident light intensity. On the other hand, fresh cells and cells exposed to a low photon dose demonstrated an increase in the fullerene-related part of the EQE with increasing light intensity, i.e. a super-linear dependence of the photocurrent in this spectral range. Generation of traps in PCBM was proposed as the underlying mechanism for this effect. Perusal of our results suggests that (1) EQE dependence on the incident light intensity should be always taken into account in measuring spectral response of fresh OPV and especially of degraded devices; (2) intensity-dependent characterization provides an insight to the degradation mechanisms of OPV and can help to separate degradation in absorption/generation from degradation of the charge collection in the cell.
•Analysis of light intensity dependence of the OPV EQE is presented.•It is a powerful tool for tracing mechanisms of the OPV degradation.•Charge collection deterioration dominates in the observed OPV degradation.•It is manifested in the decrease of EQE with light intensity.•Opposite effect is observed in the fullerene-related parts of some EQE spectra.