The RTNN hosts a collaborative REU site that leverages the strength of collaborative research on hybrid materials, specifically hybrid perovskites, together with the integrated nanotechnology tools of the RTNN to provide a state-of-the-art research experience on a timely research topic that has direct and tangible technological applications (e.g. solar cells, lighting, lasers). Each year, twelve students conduct research in faculty labs across the three RTNN institutions: the University of North Carolina at Chapel Hill, North Carolina State University, and Duke University. The project is led by Professors Jim Cahoon (UNC), David Mitzi (Duke), and Aram Amassian (NC State).
Hybrid perovskites are exciting materials that enable state-of-the-art technology for solar cells, lighting, lasers and more. We are seeking undergraduate applicants to experience novel research on this topic during Summer 2022 under the guidance of renowned faculty at UNC-Chapel Hill, NC State University, and Duke University. Participating faculty span the departments of Chemistry, Physics, Materials Science, and Applied Science.
- ~12 students will be supported for 10 weeks – starting late May through July
- Students will experience hands-on contemporary research topics on hybrid organic-inorganic materials including synthesis and processing, modeling and characterization, and device fabrication and testing
- Applicants must be enrolled in an undergraduate degree program and be a US Citizen or permanent resident
To strengthen inter-institutional relationships, each student partners with a peer working on a complementary project at a different RTNN university. Team-building, professional development, and social activities are interwoven into the program schedule.
There are three objectives for this REU program: (1) To provide a hands-on research experience in hybrid perovskite materials that reinforces student knowledge of cutting-edge characterization techniques and analytical tools that can be used to evaluate the nanoscopic structure of hybrid perovskite systems; (2) to foster student interest in pursuing a career in STEM fields, especially those from underrepresented groups; and (3) to develop communication and networking skills in each of the participants.
- Application Deadline: February 18, 2022
- Letters of Recommendation due: TBD
- Chosen applicants will be notified by March 15, 2022
Faculty Mentors and Example Projects
The following are examples of the types of projects you could expect to participate in this summer. The application will ask you to choose a top 5, so please refer to these as you apply:
“Layered Perovskite Organic/Inorganic Hybrid Photovoltaics” (Prof. Harald Ade, NC State)
Perovskite based organic/inorganic hybrid photovoltaics have attracted a tremendous focus in the past few years. With the recent record power conversion efficiency of more than 23%, this technology is already at the edge of mass scale industry production. However, to make this technology an everyday reality, two major concerns still demand deep exploration: (1) understanding the fundamental structure-property relationship in this organic/inorganic hybrid system, and (2) environmental stability of these devices as far as the fabrication/manufacturability and operation are concerned. Understandably, both these issues are connected to the solid-state film microstructure and their charge transport dynamics. The Ade group focuses on studying the film microstructure to understand the basic structure-property relationship of these layered hybrid systems. The RT-REU student’s project would focus on tandem solar cells. This is a device strategy that seeks to improve performance by implementing improved interface properties and controlling blend morphology. The student will combine knowledge gained from morphological studies to understand the role of microstructures on device performance and long-term stability. The REU student will first reproduce known solar cell results as a reference while they focus on developing a novel processing method, which will allow desired material organization and interface structure. This requires extensive initial effort with structural and spectroscopic characterization.
“On-Chip Hybrid Perovskite Single Crystals Semiconductors” (Prof. Aram Amassian, NC State)
Hybrid perovskite semiconductors have been shown to be easily processed into macroscopic single crystals (SCs) of high quality despite being grown from solution at low temperature, opening new opportunities for manufacturing high-performance, bespoke single-crystal semiconductors. While standalone SCs are easily synthesized, directly growing SCs on foreign substrates is considerably more important technologically but also particularly challenging due to the preponderance of heterogeneous nucleation. RT-REU students joining the Amassian lab will be exposed to all aspects of SC synthesis and formulation engineering and will benefit from the expert help of a graduate student and the PI’s encouragement to find creative ways of synthesizing SCs directly on surfaces. The Amassian lab has found that integrating REU students as full members of the research team in high value projects allows them to experience the life and pace of a researcher and provides a vested interest by the mentor and other lab members in the success of the REU student’s project. The student will be given the opportunity to choose between a project focusing on the synthesis side of SCs, such as by developing approaches for obtaining large SCs of new material formulations, or to focus instead on integration of SCs onto crystal-line substrates via direct printing techniques, followed by qualitative and quantitative characterization of crystals and their physical properties; alternatively, a student more inclined toward device fabrication will be given the opportunity to design new ways of patterning SC arrays on substrates toward their integration into optoelectronic or electronic devices. Students will be mentored daily and will participate in weekly group meetings to present their progress and receive feedback.
“Computational Discovery and Understanding of Tailored Hybrid Perovskites” (Prof. Volker Blum, Duke)
The Blum group focuses on quantum-mechanical, electronic structure based computational predictions of structure and properties of new materials, with a strong focus on developing new computational methods based on electronic structure theory. Through long-term, joint developments led by Blum, the group is connected to a large, international community of researchers, including the FHI-aims all-electron electronic structure code and the open-source “ELSI” infrastructure, which bridges several leading electronic structure software packages. Blum’s group is also involved in a separate NSF-funded project “HybriD3”, focused on broadening the materials space of new hybrid perovskites, as well as in a DoE Energy Frontier Research Center, “Center for Hybrid Organic-Inorganic Semiconductors for Energy” (CHOISE), focused on elucidating the physics of emergent phenomena such as spin, charge and light-matter interactions in new organic-inorganic hybrids. The undergraduate researcher in this project will use electronic structure methods to elucidate questions related to tailored structure (e.g. by incorporating chiral molecules to manipulate spin and chiroptical properties) and energy band structures of complex hybrid perovskites, using state-of the-art computational approaches that can nevertheless be learned by a sufficiently motivated undergraduate student. Mentoring will be provided by Blum as well as by a senior Ph.D. student or postdoctoral researcher in the group. The student will also be trained in using advanced computational research equipment effectively, e.g.supercomputers such as those accessible through NSF’s XSEDE infrastructure. A current undergraduate research advisee of Blum, Tommy Lin (Duke Chemistry), is using TACC’s Stampede2 computer for electronic structure based simulations.
“CVD Growth, Conversion, and Passivation of Hybrid Perovskites” (Prof. James Cahoon, UNC)
Chemical vapor deposition (CVD) methods are widely used to synthesize thin film and nanostructured semiconductors, yet a robust method to synthesize hybrid perovskites by CVD has not been developed. The Cahoon group recently reported the vapor-liquid-solid (VLS) synthesis of lead halide nanowires and their conversion to hybrid perovskites using a CVD process. Hybrid perovskites such as MAPbI3 are often formed by the intercalation of an organic halide with a lead halide, such as the introduction of methylammonium iodide (MAI) into a lead iodide (PbI2) crystal lattice. For hybrid perovskites, these reactions are typically performed in the solution phase rather than vapor phase through a CVD type process, yet vapor-phase processes can potentially produce higher quality, pure materials and retain the morphology of the initial materials. RT-REU students will study the vapor-phase growth and conversion of lead halide and perovskite materials using a custom-built CVD in the Cahoon group. This one-of-a-kind CVD systems features vapor-phase precursors including tetraethyl lead, monomethylamine, HCl, HBr, and
HI gases. These gases are safely introduced into a thermal reactor with pressure, temperature, and flow rates all under computer control. Using this system, researchers can study both the direct growth of hybrid perovskites and the conversion of lead halides to perovskite, as well as the vapor-phase passivation of perovskites using individual component gases. Studies will be performed on materials grown in-house as well as on single-crystals obtained from RT-REU collaborating groups (e.g. Huang, You). RT-REU students will learn the principles of CVD processes and characterization techniques available in RTNN facilities, including scanning and transmission electron microscopy, energy-dispersive x-ray spectroscopy, atomic force microscopy, and photoluminescence spectroscopy. They will develop skills in LabView and MatLab data collection and analysis and receive training on literature review, oral presentations, and manuscript preparation. In addition to RT-REU activities, students will participate in and present at sub-group and group meetings.
“Charge Carrier Dynamics in 2D Hybrid Perovskites” (Prof. Gundogdu, NC State)
The REU student on this project will study optically excited carrier dynamics in various hybrid perovskite thin films using time resolved spectroscopy techniques existing in the Gundogdu lab. The goal of the research will be revealing exciton charge separation, relaxation, and recombination kinetics in designed hybrid perovskites structures. The student will work on 2D layered perovskites in which both the organic cation layer and the inorganic components are optically active. In other words, depending on the photon energy, optical excitations create carriers in organic, inorganic or in both of the component. The relative alignment of the electronic energy levels and the electronic coupling between the component materials leads to tunable electronic properties. As a result, this material system can be basis of many optoelectronic applications such as solid-state lighting and photovoltaics. The REU student will contribute to these studies by performing linear optical absorption and ultrafast differential transmission experiments. In the time resolved experiments a tunable laser source with 100 fs pulse out is used to excite the material, and a broadband probe pulse measures the population in different electronic states at various time delays. By tuning the excitation pulse across the absorption bands of the material, the student will selectively excite the organic or inorganic component of the material and investigate resulting dynamics. The outcome of these studies will be used to design perovskite based electronic materials.
“Flexible Perovskite Solar Cells as Battery Replacements” (Prof. Jinsong Huang, UNC)
In this project, a REU student will be trained to use the blading method to make high efficiency perovskite solar panels on flexible indium tin oxide (ITO) substrates. More importantly, the REU student will demonstrate the possible applications of flexible solar panels by integrating the them into existing systems that currently require batteries. Specifically, the undergraduate student will identify at least one application, such as a solar panel on a toy car or an unmanned remote-controlled aircraft. The area of the solar panels will be determined by the power requirements of the application. Voltage converters will be applied to match the voltage requirement. The shape and weight of the solar panel and converter will also be taken into consideration. The student will learn how thin-film solar cells work and the processes to make a thin film solar cell and a large-area solar module. The students will learn the advantages of photovoltaic cells based on hybrid perovskites, including simplicity to fabricate, low cost, high efficiency, and lightweight, by considering these properties in real applications. This project will also demonstrate the broader impact of hybrid perovskite materials by providing a clean renewable energy source.
“First-Principles DFT of Chemically-Substituted Perovskites” (Prof. Yosuke Kanai, UNC)
The Kanai group works on development and application of computational methods based on first-principles electronic structure theory for obtaining the understanding at the atomistic level. By applying large-scale density functional theory simulation methods, the REU student will work closely with graduate students and post-doctoral researchers to investigate how chemical substitution in an organic-inorganic hybrid perovskite change its optical and electronic properties. The REU student will learn a wide range of scientific concepts in chemistry and solid states physics and also develop computational skills, including the use of Unix-operating environment and performing computer simulations of molecules and materials on modern massively-parallel computers.
“Perovskite Photovoltaics (PVs) with Simplified Device Structure” (Prof. Jie Liu, Duke)
While perovskite PVs have generated tremendous interest for ultra-low-cost solar energy, device design is complex. Carrier-transport-layer-free (CTL-free) architectures (i.e. architectures without distinct electron- and hole-transport layers) are promising designs, offering simpler configuration and lower-cost processing for next-generation perovskite PV. However, without distinct CTLs, the photoexcited carrier (e.g. electron/hole) collection generally becomes less effective. Lattice mismatch between perovskite films and electrodes can also generate a significant concentration of surface defects, leading to severe surface recombination. In this project, the student will focus on understanding the mechanisms governing CTL-free interfaces and seek to tailor the perovskite film compositions to suppress interfacial carrier loss to recombination. As chemical compositions determine energy band structures, this project will engineer perovskite materials through component substitution and/or doping to tailor the energy band and/or Fermi-level positions, aiming for better band alignments to eliminate interfacial energy barrier(s). The RT-REU student will learn to synthesize perovskite films, fabricate solar cells, and perform PL measurements. The student will vary the substrate and monitor the PL and PV performance of the resulting materials.
“Experimentally Exploring Additive Engineering and Structural Versatility in Perovskites”(Prof. David Mitzi, Duke)
Halide perovskites represent a diverse collection of structures ranging from strictly inorganic to organic-containing and from zero- to three-dimensional connectivity within the underlying framework. These semiconductors offer an unprecedented opportunity for tailoring outstanding electronic structure characteristics for optoelectronic devices, including a direct and tunable band gap, small electron/hole effective masses leading to balanced carrier transport, and defect tolerance (or resistance to non-radiative recombination). Furthermore, this materials family can be processed cheaply and effectively using a number of simple solution- and vacuum-based approaches. One project relates to understanding the impact of targeted additives during film deposition on physical properties and device performance. State-of-the-art characterization approaches will be employed to pursue additive-property relationships. For example, additives such as excess lead iodide have been found to tune carrier density and recombination characteristics, while addition of methylammonium thiocyanate during solution processing substantially increases grain size. A second project relates to developing new hybrid perovskites that contain complex organic cations, with the innovative cations targeted toward certain functional characteristics (i.e. suited to charge transfer, doping or light emission). Careful design can lead to validation of the idea that such structures are self-assembling analogs to multilayer quantum well structures. The extent to which the organic-inorganic versions can also introduce synergistic functionality (i.e. the properties of the hybrid perovskite are more than the sum of organic and inorganic characteristics) will be explored by connecting to crystal structure-property relationship.Tools and approaches employed for both projects may include crystal growth, film deposition by spin coating, X-ray diffraction, UV-visible-near-IR spectroscopy, photoluminescence and Hall effect.
“Compositional Engineering in Perovskite Light Emitting Diodes” (Prof. Franky So, NC State)
The proposed research will be a study of quasi-2D perovskites to uncover their structural-property relationship in this class of materials for lasing operation. The objective is to gain an in-depth understanding of the effects of the perovskite composition, crystallinity, crystal dimensionality, nanoscale morphology on polaron formation, energy relaxation kinetics, and amplified spontaneous emission thresholds, and the outcome is to establish a set of perovskite material design rules leading to a big step forward toward the realization of room temperature CW operation lasers emitting in all colors in the visible spectrum. The REU student is expected to be involved in synthesis of quasi-2D perovskite thin films and their characterization. The characterization techniques include x-ray diffraction, atomic force microscopy, UV-VIS spectrophotometry, and photoluminescence measurements.
“Matrix-Assisted Pulsed Laser Evaporation of Perovskite” (Prof. Adrienne Stiff-Roberts, Duke)
Energy efficient, white-light, light-emitting diodes (LEDs) are an important technology for solid state lighting applications; yet, state-of-the-art III-N LEDs have modest color purity such that they cannot provide optimum color rendering. Recently, perovskite-based devices have demonstrated color purity comparable to colloidal quantum dots, making them an exciting technology option to exceed industry standards for chromaticity. In addition, perovskite-based materials possess several properties that motivate their use in LEDs. Despite these advantages, the best external quantum efficiency (EQE) values that have been achieved for perovskite LEDs are 3.5% in the near-infrared and 8.5% at green wavelengths, which is much less than the EQEs attained in other high-performance solution-processed materials (> 20%).Stiff-Roberts used resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) to deposit MAPbI3 perovskites for solar cells.These films tend to be thinner, and they have inherently smaller grain sizes compared to solution-processed films. Due to the low exciton binding energies in hybrid perovskites, LEDs could benefit from exciton spatial confinement (nanoscale grains plus ultra-thin films) for efficient radiative recombination. The hypothesis to be investigated in the REU project is that RIR-MAPLE enables ultra-thin-film (< 30 nm) hybrid perovskites that are pinhole-free with compact, nanoscale grain sizes to reduce leakage currents and improve EQE. The REU research project tasks are to perform standard materials characterization and to demonstrate increased EQE due to ultra-thin films/nanoscale grains in emitter layers grown by RIR-MAPLE.
“Perovskite-Based Spin-optoelectronic and Terahertz devices” (Prof. Dali Sun, NC State)
Sun’s research group focuses on studying the spin-dependent optoelectronic and Terahertz (THz) device physics at GHz to THz timescale using 3D, 2D, and reduced dimensional hybrid perovskites materials. The REU students will be trained to operate a glove box integrated deposition system in Sun’s lab and will assist in fabricating hybrid perovskite-based spin-optoelectronic devices including light-emitting diodes and spin-transfer torque devices. The REU students will be trained to fabricate hybrid perovskite-based spintronic THz sources in a project that was recently funded by NSF EPMD program in close collaboration with Prof. Wei You’s group at UNC and Prof. Kenan Gundogdu’s group at NC State. Working with the senior graduate students in Sun’s group, the REU students will learn to develop LabVIEW programs and variable-temperature high-field photoluminescence set up for characterizing the magneto-optical properties in various hybrid perovskite thin films and single crystals.
“Novel Hybrid Perovskites with Tailored Organic Cations” (Prof. Wei You, UNC)
The Youlab is interested in advancing research and education in the area of novel organic/inorganic hybrid perovskites for fundamental understanding and a variety of applications. RT-REU student participants in the You lab will work with a graduate student and the PI to learn all aspects of hybrid perovskites, including synthesis, characterization of fundamental properties, and device fabrication and testing. Depending upon the REU student’s own research interest and research experience/background, the REU student will be supervised by the graduate student mentor on a specific project, either synthesis (organic and/or inorganic synthesis) oriented or device focused. The graduate student mentor will provide day-to-day mentoring with support from all members of the You lab, including the PI. The You lab has found this is the best strategy to support the REU student’s growth as an independent researcher while broadening his/her research experience through group meetings and interactions with all lab members. Moreover, due to the multidisciplinary nature of these projects, the REU student will have the opportunity to participate in project-focused group meetings to interact with researchers at other institutions (Duke and NC State).
This material is based upon work which is supported by the National Science Foundation (award numbers 2050900, 2050841, & 2050764). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.