Further anthropogenic climate change can be prevented as renewable power becomes more cost effective. Organic photovoltaic (OPV) solar cells provide opportunities for low cost renewable energy technology. Since improved materials are critical to commercial viability, the goal of our work is to develop and characterize more effective, low cost, sustainable and synthetically scalable molecules (e.g. Squaraines), to facilitate effective mass production of solar cells. Our work leverages new theoretical models that will successfully simulate experimental measurements made on representative compounds such that future chemical formulas can be chemically tuned to an optimal prescriptive design. Our work leads to a universally applicable understanding in chemistry, materials science, theoretical modeling and device engineering, for all participants.
Current Research Directions
The promise of organic photovoltaic (OPV) solar cells currently suffers through low efficiencies and high manufacturing costs, both rooted in difficulties associated with attaining tight polymer morphology control. Squaraines address the resulting need for new easily-purified, consistently processable, low-band-gap small molecules that can be chemically tuned to a prescriptive design, based upon comprehensive theory co-developed in our group. In recent years, higher efficiencies have been measured with "push-pull" or Donor-Acceptor (D-A) type compounds designed to address bandgap and energy level requirements. Yet, the field fundamentally lacks a strong prescription to optimize materials for all critical properties that combine to provide optimal performance. Hence, our group leverages new theoretical models that will successfully simulate the morphology-based spectroscopy for a series of squaraines, compounds representative of the total set of D-A type OPV-targets. The theory will describe how morphological and molecular structure influences the absorption spectrum, the excited states and the intermolecular charge transfer integral. Thus, when the models are validated through measured spectroscopy, the complete understanding will lead to a prescriptive design for idealized materials optimized for all critical properties in OPV (solar spectrum absorption overlap, exciton diffusion, exciton dissociation and charge transport).
In parallel, with the evolving theory of the structure-function relationship, squaraines can be modified for processing in non-toxic solvents. The long term goal is to develop and characterize low cost, sustainable and scalable-synthesized materials with improved properties to facilitate effective mass production of solar cells. A summary of the goals for our group are:
- To deliver a comprehensive understanding of the excited state properties of representative OPV materials (e.g. Squaraines).
- To verify the comprehensive understanding with materials characterization and optical spectroscopy in a range of different environments.
- To confirm that all critical properties (absorption, mobilities, exciton diffusion length etc.) for device operation have been improved through device manufacture and testing
- Combining these approaches, the target OPV materials will be used as robust and predictable mechanistic probes for a better, consistent and fruitful understanding of the universal OPV device.
- Finally, synthesis will allow for vastly improved materials; in particular, materials can be prescriptively functionalized for processing in non-toxic solvents, ready for mass production.
The rapidly increasing circle of collaborative and iterative progress (theory, simulation, characterization, synthesis, repeat) will lead to the design and prediction of superior materials and techniques for mass production of optimized bulk heterojunction OPVs. Our work therefore addresses the interrelated challenges of sustainable engineering, production, and use of chemicals and materials.
- National Science Foundation
About Dr. Christopher Collison
Dr. Chris Collison is a Professor in the School of Chemistry and Materials Science in the College of Science, a core faculty member in the Microsystems PhD Program in KGCOE and an Extended Faculty in Materials Science and Engineering. He holds a BSc and PhD in Chemistry from Imperial College, London and a Diploma of Imperial College in Photophysics. In his doctoral research under Dr. Garry Rumbles he discovered the first direct evidence for luminescent interchain states in a conjugated polymer. In 1996, As a post-doctoral research fellow mentored by Dr. Lewis Rothberg, Chris worked with transient absorption, aggregation phenomena, and conjugated polymers for organic LEDs. Chris Joined RIT in 2004 after an appointment as Photophysics Research Scientist at the University of Rochester and an industrial position as Applications Scientist at Newport Corporation (Richardson Gratings).
Chris' research thrust is the design and development of organic solar cells using computational theory, spectroscopy and device manufacture, engineering and testing. Chris is the director of the RIT-OPV Research Experience for Undergraduates program. He is approaching $1M in external funding. He has been the advisor to 32 undergraduate research students (16 are co-authors on peer-reviewed publications), 10 MS students and 2 PhD students. Chris has published more than 20 journal articles collectively cited over 1300 times, he teaches courses in physical chemistry and molecular photophysics, and received the Provost’s Award for Excellence in Faculty Mentoring, RIT 2013.
Dr. Collison greatly values his experience of working both in industry and in academia, and recognizes the importance of life-long, principles-based personal development and growth. He applies these universal principles as a guide in all that he does. He seeks first to understand the views of all parties before taking personal action. He strongly encourages an egalitarian and inclusive approach. He strives to be honest, direct, transparent and objective. He encourages others to follow suit for mutual benefit.
- Chenyu Zheng, Michael F. Mark, Tyler Wiegand, Steven A. Diaz, Jeremy Cody, Frank C. Spano, David W. McCamant, Christopher J. Collison, "Measurement and Theoretical Interpretation of Exciton Diffusion as a Function of Intermolecular Separation for Squaraines Targeted for Bulk Heterojunction Solar Cells" J. Phys. Chem. C, 124 (7), 44032-4043, (2020)
- C Zheng, A Raju Penmetcha, B. Cona, S. Spencer, B. Zhu, P. Heaphy, J. Cody C Collison "The contribution of aggregate states and energetic disorder to a squaraine system targeted for organic photovoltaic devices", Langmuir, 31 (28), 7717–7726 (2015)
- S Spencer, J Cody, S Misture, B Cona, P Heaphy, G Rumbles, J Andersen, C Collison "Critical Electron Transfer Rates for Exciton Dissociation Governed by Extent of Crystallinity in Small Molecule Organic Photovoltaics" Journal of Physical Chemistry C, 118, 14840–14847 (2014).
- SD Spencer, C Bougher, PJ Heaphy, VM Murcia, CP Gallivan, A Monfette, JD Andersen, JA Cody, BR Conrad, CJ Collison “The effect of controllable thin film crystal growth on the aggregation of a novel high panchromaticity squaraine viable for organic solar cells.” Solar Energy Materials and Solar Cells 112, 202–208, (2013).
- S Spencer, H. Hu, Q. Li, H-Y Ahn, M. Qaddoura, S Yao, A. Ioannidis, K. Belfield, CJ Collison, "J-aggregate formation for increased short-circuit current and power conversion efficiency with a squaraine donor." Progress in Photovoltaics, DOI: 10.1002/pip.2289, (2012).