Lessard Research Group - Next Generation Materials for Next Generation Applications

New publication in J. Mater. Chem. C!

Silicon phthalocyanines as dopant red emitters for efficient solution processed OLEDs.


The optical characterisation and device functionality for a series of axially modified silicon phthalocyanines (SiPcs) as dopant red emitters in solution-processed and vapour-deposited organic light-emitting diodes (OLEDs) is presented. Control over the axial group composition enables bandgap maintenance around 1.8 eV and photoluminescence quantum yield values of up to 66% in solution. We confirm efficient energy transfer between a polyfluorene host matrix and a SiPc dopant under photoexcitation, and demonstrate solution-processed OLED devices with narrow electroluminescence spectra (20 nm full-width at half-maximum) close to 700 nm. Vapour-deposited OLEDs based on TCTA as host exhibit characteristic SiPc emission around 715nm, but with greater spectral contamination from the host. An initial OLED optimisation exercise demonstrates external quantum efficiencies of up to 2.5% in solution-processed devices, indicating that such phthalocyanines may prove promising red dopant emitters for OLEDs with high colour purity.

Find it in Publication section

To read the full article visit J. Mater. Chem C.

New Publication in J. Mater. Chem. A! Congrats Trevor!

Bis(tri-n-alkylsilyl oxide) silicon phthalocyanines: A Start to Establishing a Structure Property Relationship as both Ternary Additives and Non-Fullerene Electron Acceptors in Bulk Heterojunction Organic Photovoltaic Devices

Previous studies have shown that the use of bis(tri-n-hexylsilyl oxide) silicon phthalocyanine ((3HS)2-SiPc) as a solid ternary electroactive additive in poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester P3HT:PC61BM bulk heterojunction organic photovoltaic (BHJ OPV) devices resulted in an increased performance. It has been hypothesized that the increase in efficiency is partially due to the unique and odd combination of high solubility and strong driving force of crystallize previously observed for (3HS)2-SiPc. In this follow up study, two chemical variants of (3HS)2-SiPc, bis(tri-n-butylsilyl oxide) ((3BS)2-SiPc) and bis(tri-n-isopropylsilyl oxide) ((3TS)2-SiPc) were synthesized to determine how small changes in chemical structure would affect the properties of the material and its performance within BHJ OPV devices. We observed that the use of either (3XS)2-SiPc compound results in a further ~10% increase in Jsc compared to the use of (3HS)2-SiPc. We also did a preliminary assessment of the use of the three (3XS)2-SiPcs as replacements for PC61BM in straight binary P3HT-based BHJ OPV devices. Despite achieving only ~1% PCE efficiencies, observations including a ≈ 50% increase in VOC over a P3HT:PC61BM baseline and a decent fill factor indicate to us that (3XS)2-SiPcs do have potential as non-fullerene acceptors and advantageous alternatives due to their low embedded energy and therefore their inherent sustainability. X-ray diffraction of ternary and binary BHJ devices demonstrate that both (3BS)2-SiPc and (3TS)2-SiPc experienced similar increase in crystallite density (d-spacing) relative to (3HS)2-SiPc which we surmise plays a role in the improved device efficiency. Like (3HS)2-SiPc, for these two new additives, we also observed a high tendency to crystallize. The results from this study suggest that solubility and driving force to crystalize are important factors in determining the extent to which an additive will migrate to the donor/acceptor interface and thus affect its performance as a ternary additive in BHJ OPV device. Based on the three (3XS)2-SiPcs used in this study, the smaller tri-n-alkylsilyl oxide molecular fragments seem to work better. Therefore, moving forward, we will continue to consider smaller molecular fragments that still enable solubility and processability of (3XS)2-SiPcs.

Find it in Publication section

To read the full article visit J. Mater. Chem A.


Cleaning up at the uOttawa Engineering Poster competition!

The Faculty of Engineering Hosts the Annual 2017 Engineering and Computer Science Graduate Poster Competition.

This annual research competition among the graduate students of the Faculty of Engineering, not only demonstrates the cutting-edge research that the Faculty’s graduate students are conducting, it also gives Ottawa’s industry and community a sneak preview of the next generation of designers, innovators, and entrepreneurs. (Link to website)

This year Owen Melville and Trevor Grant, two PhD students from the Lessard Research group discussed their recent results resulting in 2nd and 3rd place, respectively. This is a repeat performance for Mr. Melville who received 2nd place for his poster at the 2016 competition.


Congrats Trevor! New Publication in J. Mater. Chem A!

New Publication in J. Mater. Chem A!


Great improvements in the development of organic photovoltaic devices have been reported over the years; however, the overall efficiency and operational lifetimes of the devices must be improved. Maintaining an optimal morphology of the device active layer over time and with exposure to heat is vital to achieving a stable power conversion efficiency (PCE), currently achieved by utilizing cross-linkable ternary additives to lock in the film morphology. However, these additives currently do not contribute to improving the PCE of the device therefore limiting their overall effectiveness. In this study we present a dual functional bis(6-azohexylacrylate) silicon phthalocyanine ((HxN3)2-SiPc) with cross-linking groups and near IR absorption as a ternary additive in poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PC61BM) devices. As an additive, (HxN3)2-SiPc increased the short circuit current density (Jsc) by ≈ 9% due to increased photocurrent generation in the near IR region. In addition, devices utilizing (HxN3)2-SiPc exhibited a 97% PCE retention after thermal ageing at 150 °C for 23h (compared to 47% retention for baseline devices) showing the compound is an effective cross-linker. These findings represent the first example of a multifunctional dye additive in an OPV device that simultaneously broadens the spectral coverage, resulting in added photogeneration, and stabilizes the active layer morphology, resulting in increased PCE retention.


Find it in Publication section

To read the full article visit J. Mater. Chem A.