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Feasibility of inkjet printing as a viable solar cell fabrication method
Thesis   Open access

Feasibility of inkjet printing as a viable solar cell fabrication method

Brandon Scott Lee
Master of Science (M.S.), Drexel University
Jun 2012
DOI:
https://doi.org/10.17918/etd-4119
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Abstract

Organic electronics Biosensors Mechanical Engineering
In this study, the flexible polymer substrate polyethylene naphthalate (PEN) was modified under two different plasma chemistries, namely helium-oxygen (He-O2) and helium-water vapor (He-H₂O) plasmas at atmospheric pressure and room temperature. Surface changes related to wettability, chemical functionalization, surface energy, and morphology after plasma treatment were investigated using water contact angle (WCA) goniometry, x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Each plasma resulted in a more hydrophilic PEN surface, with WCA decreasing by 68% and 85% for He-O2 and He-H₂O plasma treated PEN, respectively, after only 1.0 second of exposure. An aging study of plasma treated PEN shows an increase in WCA that is still 30° lower than that of the as-received PEN after one month. XPS and AFM results show that improved wettability of the plasma modified PEN is due to the oxidation of the surface and not due to the increased surface roughness. To promote a roll-to-roll process of tmospheric plasma treatment and inkjet deposition, printing was performed using the conductive polymer poly(3,4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT:PSS) on the as-received and plasma treated PEN surfaces where the shape and morphology of the lines were studied. Each plasma treated PEN surface exhibited well-defined, uniform inkjet-printed lines due to the improved wettability and increased surface energy. After scanning electron microscopy (SEM) analysis of the PEDOT:PSS dispersion of a single drop on each substrate, the He-H₂O plasma treated surface led to less agglomeration of PEDOT:PSS and a more homogeneous drop deposit. This study also focused on the feasibility of inkjet printing organic solar cells consisting of an active layer of poly(3-hexylthiophene):phenyl-c61-butyric acid methyl ester (P3HT:PCBM) on zinc oxide (ZnO) coated indium tin oxide (ITO) glass slides. The inkjet printing frequency, drop spacing, and effect of multiple layers were investigated by analyzing optical images of the inkjet printed P3HT:PCBM active layers. From these images the optimal parameters were determined and consisted of 1.5 kHz inkjet printing frequency, 65 [mu]m drop spacing, and two layers printed in a crossed pattern. After determining the optimal parameters, solar cell testing was conducted on the inkjet printed organic solar cells. The solar cell testing consisted of using a solar simulator in order to measure the absorption spectrum for the inkjet printed P3HT:PCBM films and the I-V curves for the inkjet printed organic solar cells. From the I-V curves generated it can be seen that the two layers crossed organic solar cell provided the best results.

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