Improved light utilization efficiency for an ITO‐free semi‐transparent organic solar cell using a multilayer silver back electrode as infrared mirror
Leonie Pap, Bertolt Schirmacher, Esther Bloch, Shankar Bogati, Philipp Viehmann, Arnulf Scheel, David Müller, Mathias List, Birger Zimmermann, Uli Würfel- Electrical and Electronic Engineering
- Energy Engineering and Power Technology
- Atomic and Molecular Physics, and Optics
- Electronic, Optical and Magnetic Materials
Semi‐transparent organic solar cells (STOSC) exhibit promising application as power‐generating windows in buildings and agricultural greenhouses. Due to the unique optical properties of organic semiconductors they can efficiently absorb near infrared light while maintaining a high degree semitransparency in the visible range. Since power conversion efficiency (PCE) and average visible transmission (AVT) frequently stand in a trade‐off relationship, a major challenge in improving the overall performance of STOSCs is maximizing the product of both, called the light utilization efficiency (AVT × PCE = LUE). Herein we propose using multiple layers of Al‐doped ZnO (AZO) and silver (Ag) as an infrared reflecting back electrode, in order to increase current generation while maintaining a high visible transparency. By using optical modelling, the optimal layer thickness of the AZO layer sandwiched between two Ag layers is determined leading to an increase in photocurrent generation of up to 10%. Simultaneously, experimental findings show that the fill factor decreases with an increase of the AZO layer thickness. By further adjusting the thickness of the photoactive layer, the blend concentration as well as improving the top electrode material we are able to attain the thus far highest reported LUE for ITO‐free STOSC, reaching 4.0% with a PCE of 8.7% and an AVT of 46.3%.
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