(7gr) Solution Processed Optoelectronics. Materials to Devices

Research Experience. Solution processing has the potential to become a transformative technique for producing photovoltaics at both the low cost and large scale needed to meet energy demand, yet many challenges remain for both materials and devices. During my Ph.D. research, under the direction of Prof. Prashant Kamat and the University of Notre Dame, I applied ultrafast transient spectroscopy to probe charge recombination and charge transfer across semiconductor heterojunctions with specific relevance to solution-processed photovoltaics. In addition to these spectroscopic studies, I led our group’s efforts investigating lead halide perovskite photovoltaics, developing novel device architectures and elucidating the mechanism of moisture-induced degradation. This work led to the publication of my thesis entitled, “Mesostructured Thin Film Solar Cells: Examining Hole Transfer Mechanisms and Device Stability” which earned me the Eli J. and Helen Shaheen Graduate School Award in Engineering.

During my postdoctoral work as an EERE Postdoctoral Fellow at the National Renewable Energy Laboratory (NREL), I have worked to address the challenges associated with solution processed halide perovskite solar cells. While these materials have already reached 22% efficiency, their stability remains a hurdle on the path toward commercialization. At NREL, I have utilized a suite of characterization techniques and formed numerous fruitful collaborations to investigate degradation processes in halide perovskite materials while simultaneously working to fundamentally improve their stability and performance. This has led to a greater understanding of degradation process and material properties, and led to the development of perovskite solar cells which remain largely unchanged despite 1000 hours of continual, unencapsulated operation.

Future Direction. I am excited by the potential of solution-processed optoelectronic devices, including photovoltaics, light emitting diodes, and dynamic windows, and the potential these devices have for transforming the energy sector. However, bringing solution-processed optoelectronic devices from the lab to the market requires a better understanding of the materials themselves, including the development of new materials, and solution-based formation/deposition processes that enable material formation and scalable device fabrication. As a faculty member I intend to develop a research program that addresses both of these materials challenges, materials and their formation, and applies this understanding to the fabrication of devices. Specifically, I intend to work with materials, particularly halide perovskites because of their GaAs-like optoelectronic properties, across length scales, from nanoparticles to large-area thin films and single crystals, to better understand the effects of surface chemistry, grain boundaries, and defect chemistry on material properties. This will enable the rational design of materials for optoelectronic devices. In tandem with this work, I aim to enable the scalable manufacturing of these materials and devices my moving beyond traditional material synthesis and deposition techniques. I will work to develop inherently scalable material formation techniques, including blade coating and spray coating, by understanding and controlling the kinetics and mechanisms of film formation. These two thrusts are highly complementary and will allow for iterative feedback within the research group as well as exposing new areas for investigation.

Teaching Interests:

During the 2014-2015 academic year, I served as the instructor for Introduction to Engineering Systems I & II at the University of Notre Dame, an introductory level engineering course of 40+ students. As one of seven instructors across all of the sections of this course, I collaborated with senior Notre Dame faculty members to develop lecture and exam materials, gaining valuable insight into both teaching and course design. In addition to this teaching experience, during my doctoral education I received guidance through teaching workshops hosted by the University of Notre Dame Kaneb Center for Teaching and Learning and was awarded the Advanced Teaching Scholar Certificate.

I enjoy devising unique examples and problems to help students learn difficult concepts. I frequently use in-class examples and activities to help students learn from their peers and help me better gauge student learning, allowing me to better address specific weaknesses in future lectures and avoid wasting time on material where they already show proficiency. In addition, I find this keeps lectures interactive, engaging, and unique from the textbook.

Beyond the classroom, I have participated in mentoring five undergraduate students and two high school teachers in their research. This has helped me develop my skills as a research mentor and has led to two second author research papers for undergraduates I mentored.

Selected Publications:

Christians, J. A.; Schulz, P.; Tinkham, J. S.; Schloemer, T. H.; Harvey, S. P.; Tremolet de Villers, B. J.; Sellinger, A.; Berry, J. J.; Luther, J. M. Tailored Interfaces of Unencapsulated Perovskite Solar Cells for >1000 Hours of Ambient Operational Stability. 2017, under review.

Swarnkar, A.; Marshall, A. R.; Sanehira, E. M.; Chernomordik, B. D.; Moore, D. T.; Christians, J. A.; Chakrabarti, T.; Luther, J. M. Quantum Dot-Induced Phase Stabilization of α-CsPbI₃ Perovskite for High-Efficiency Photovoltaics. Science, 2016, 354, 6308, 92-95.

Manser, J. S.; Christians, J. A.; Kamat, P. V. Intriguing Optoelectronic Properties of Metal Halide Perovskites. Chem. Rev. 2016, 116, 12956-13008.

Nenon, D. P.^†; Christians, J. A.^†; Wheeler, L. M.; Blackburn, J. L.; Sanehira, E. M.; Dou, B.; Olsen, M. L.; Zhu, K.; Berry, J. J.; Luther, J. M. Structural and Chemical Evolution of Methylammonium Lead Halide Perovskites During Thermal Processing from Solution. Energy & Environmental Science, 2016, 9, 2072-2082.

^†These authors contributed equally

Christians, J. A.; Miranda Herrera, P. A.; Kamat, P. V. Transformation of the Excited State and Photovoltaic Efficiency of CH₃NH₃PbI₃ Perovskite upon Controlled Exposure to Humidified Air. J. Am. Chem. Soc. 2015, 137, 1530-1538.

Christians, J. A.; Leighton Jr., D. T.; Kamat, P. V. Rate Limiting Interfacial Hole Transfer in Solid-State Solar Cells. Energy Environ. Sci. 2014, 7, 1148-1158.

Christians, J. A.; Fung, R. C. M.; Kamat, P. V. An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide. J. Am. Chem. Soc. 2014, 136, 758–764.