Kenneth Graham

krgr233's picture
  • Associate Professor
  • Analytical
  • Chemistry
  • Materials
353 Chemistry-Physics Building
Research Interests:

University of North Carolina at Chapel Hill, B.S. Chemistry 2006
University of Florida, Ph.D. Chemistry 2011


Our research interests are centered around a common theme of interfacial interactions and energetics, with an application oriented approach targeting the development and understanding of interfaces in organic electronics, perovskite based solar cells, organic-inorganic composites, and thermoelectrics.  In all of these application areas the various heterointerfaces play a major role in shaping the material properties or device performance.

In organic electronic devices, such as organic photovoltaics (OPVs), organic light emitting diodes (OLEDs), and organic field effect transistors (OFETs), the various interfaces present have a major influence on device performance.  These interfaces include the organic-organic interface, which for example plays a critical role in charge separation in OPVs, as well as the organic-inorganic interface, where charge injection or extraction occurs.  The energetic landscape at these interfaces, which is determined both by intermolecular interactions and interfacial molecular conformations, can drastically influence charge transport or charge separation dynamics.   To ultimately improve device level properties through obtaining a fundamental scientific understanding we aim to controllably tune interfacial properties, use various analytical techniques to probe the interface, and test the impact on device performance.

In any solar cell technology, such as the recently developed methyl ammonium lead iodide (CH3NH3)PbI3 perovskite system, the interface between the active layer and electrodes must be optimized to minimize performance losses.  For example, low energy defect states at the surface can serve as recombination centers while improper energy level alignment can result in barriers to charge collection or energetic losses during charge collection, all of which reduce the power conversion efficiency of the solar cell.  We seek to generate a better understanding of these interfaces and how they impact device performance through utilizing various optical and photoelectron spectroscopies to probe these interfaces.  Through tuning interfacial properties and comparing with solar cell performance we will be able to draw relationships between surface chemistry, interfacial energetics, and solar cell performance.

Organic-inorganic composites provide promising opportunities for a large suite of applications, including materials with novel combinations of electronic, optical, and mechanical properties.  To control these properties the surface chemistry of the inorganic-organic interface can be tuned.  For example, in a polymer-nanoparticle blend the surface chemistry of the nanoparticle may be altered such that it interacts more strongly with the polymer and thus nanoparticle aggregation will be reduced.  Furthermore, the interfacial energetics at the polymer-nanoparticle blend may be adjusted such that charges move more freely between polymer and nanoparticle.  Here we aim to understand these interfacial interactions and how they effect material properties, followed by using these interfaces to create composite materials with improved properties (such as transparent electrodes or thermoelectrics).

A major tool and analytical focus of the group is the application of various photoelectron spectroscopies to thoroughly probe the nature of the various interfaces highlighted above.  These include ultraviolet photoelectron spectroscopy to probe the valence band or ionization potentials, X-ray photoelectron spectroscopy to probe the chemical nature of the interface, and inverse photoelectron spectroscopy to probe the conduction band or electron affinities.

Graduate Training

Analytical and Materials Chemistry

Selected Publications: 

Liang, Z.; Graham, K. R.; ACS Appl. Mater. Interfaces 2015, 7, 21652. “Surface Modification of Silver Nanowires for Morphology and Processing Control in Composite Transparent Electrodes”

Graham, K. R.; Cabanetos, C.; Jahnke, J. P.; Idso, M. N.; Laban, A. E.; Ngongang Ndjawa, G. O.; Vandewal, K.; Heumueller, T.; Salleo, A.; Chmelka, B. F.; Amassian, A.; Beaujuge, P. M.; McGehee, M. D.  J. Am. Chem. Soc. 2014, 136, 9608-9618.  “Importance of the Donor:Fullerene Intermolecular Arrangement for High-Efficiency Organic Photovoltaics”

Vandewal, K.; Albrecht, S.;  Hoke, E. T.;  Graham, K. R.; Widmer, J.;  Douglas, J. D.;  Schubert, M.; Mateker, W. R.; Bloking, J. T.; Burkhard, G. F.; Sellinger, A.; Fréchet, J. M. J.; Amassian, A.; Riede, M. K.;  McGehee, M. D.; Neher, D.; Salleo, A. Nature Mater. 2014, 13, 63-68. “Efficient charge generation by relaxed charge-transfer states at organic interfaces”

Graham, K. R.; Erwin, P.; Nordlund, D.; Vandewal, K.; Li, R.; Ngongang Ndjawa, G. O.; Hoke, E. T.; Salleo, A.; Thompson, M. E.; McGehee, M. D.; Amassian. A. Adv. Mater.  2014, 25, 6076-6082. “Reevaluating the Role of Sterics and Electronic Coupling in Determining the Open Circuit Voltage of Organic Solar Cells”

Bartelt, J. A.; Beiley, Z. M.; Hoke, E. T.; Mateker, W. R.; Douglas, J. D.; Collins, B. A.; Tumbleston, J. R.; Graham, K. R.; Amassian, A.; Ade, H.; Fréchet, J. M. J.; Toney, M. F.; and McGehee, M. D. Adv. Energy Mater. 2013, 3 (3), 364-374. “The Importance of Fullerene Percolation in the Mixed Regions of Polymer-Fullerene Bulk Heterojunction Solar Cells”

Graham, K. R.; Stalder, R.; Patel, D.; Salazar, D. H.; Reynolds, J. R. ACS Appl. Mater. Interfaces. 2013, 5 (1), 63. “Morphology Control in Molecular Bulk-Heterojunction Photovoltaic Cells Through Tailor-Made Additives”

Graham, K. R.; Stalder, R.; Mei, J.; Wieruszewski, P.; Hartel, M. J.; Mei, J.; So, F.; Reynolds, J. R. Adv. Funct. Mater. 2012, 22, 4801. “Improved Performance of Molecular Bulk-Heterojunction Photovoltaic Cells through Predictable Selection of Solvent Additives.”

Patel, D. G.; Graham, K. R.; Reynolds, J. R.  J. Mater. Chem. 2012, 22(7), 3004. “Diels-Alder Crosslinking for Dye Segregation and Multi-Layer Structures in Conjugated Polymer Devices: Towards Improvement of Device Efficiency”

Graham, K. R.; Yang, Y.; Sommer, J. R.; Shelton, A.; Schanze, K. S.; Xue, J.; Reynolds, J. R.; Chem. Mater. 2011, 23 (24), 5305. “Extended π-Conjugated Pt-Porphyrins for use in Near-Infrared Emitting Organic Light Emitting Diodes.”

Ellinger, S. E.; Graham, K. R.; Shi, P.; Farley, R. T.; Steckler, T. T.; Brookins, R. N.; Taranekar, P.; Mei, J.; Padilha, L. A.; Ensley, T. R.; Hu, H.; Webster, S.; Hagan, D. J.; Van Stryland, E. W.; Schanze, K. S.; Reynolds, J. R.  Chem. Mater. 2011, 23 (17), 3805 “Donor-acceptor-donor based p-conjugated oligomers for near-IR emission”

Koldemir, U.; Graham, K. R.; Salazar, D. H.; McCarley, T.; Reynolds, J. R.  J. Mater. Chem. 2011, 21, 6480. “Electron Rich APFO Polymer with Dual Electrochromism and Electroluminescence” 

Mei, J.; Graham, K. R.; Stalder, R.; Reynolds, J. R.  Org. Lett.  2010, 12 (4), 660.  “Synthesis of isoindigo-based oligothiophenes for molecular bulk heterojunction solar cells”

Mortimer, R. J.; Graham, K. R.; Grenier, C. R. G.; Reynolds, J. R.  ACS Appl. Mater. Interfaces  2009, 1, 2269.  “Influence of the Film Thickness and Morphology on the Colorimetric Properties of Spray-Coated Electrochromic Disubstituted 3,4-Propylenedioxythiophene Polymers

PubMed Publications*: 
  • Lin, R ;Xu, J.;Wei, M ;Wang, Y.;Qin, Z.;Liu, Z.;Wu, J.;Xiao, K ;Chen, B ;Park, SM ;Chen, G ;Atapattu, HR ;Graham, KR ;Xu, J.;Zhu, J.;Li, L.;Zhang, C ;Sargent, EH ;Tan, H "All-perovskite tandem solar cells with improved grain surface passivation." Nature 603, 7899 (2022): 73-78. Details. Full text
  • Liang, Z.;Choi, HH ;Luo, X ;Liu, T.;Abtahi, A ;Ramasamy, US ;Hitron, JA ;Baustert, KN ;Hempel, JL ;Boehm, AM ;Ansary, A ;Strachan, DR ;Mei, J ;Risko, C ;Podzorov, V ;Graham, KR "n-type charge transport in heavily p-doped polymers." Nature materials 20, 4 (2021): 518-524. Details. Full text
  • Ma, K.;Atapattu, HR ;Zhao, Q.;Gao, Y.;Finkenauer, BP ;Wang, K.;Chen, K ;Park, SM ;Coffey, AH ;Zhu, C.;Huang, L.;Graham, KR ;Mei, J ;Dou, L "Multifunctional Conjugated Ligand Engineering for Stable and Efficient Perovskite Solar Cells." Advanced materials (Deerfield Beach, Fla.) 33, 32 (2021): e2100791. Details. Full text
  • Boehm, AM ;Liu, T.;Park, SM ;Abtahi, A ;Graham, KR "Influence of Surface Ligands on Energetics at FASnI<sub>3</sub>/C<sub>60</sub> Interfaces and Their Impact on Photovoltaic Performance." ACS applied materials & interfaces 12, 5 (2020): 5209-5218. Details. Full text
  • Xia, P.;Davies, DW ;Patel, BB ;Qin, M ;Liang, Z.;Graham, KR ;Diao, Y ;Tang, ML "Spin-coated fluorinated PbS QD superlattice thin film with high hole mobility." Nanoscale 12, 20 (2020): 11174-11181. Details. Full text
  • Yurash, B ;Cao, DX ;Brus, VV ;Leifert, D ;Wang, M.;Dixon, A ;Seifrid, M ;Mansour, AE ;Lungwitz, D ;Liu, T.;Santiago, PJ ;Graham, KR ;Koch, N ;Bazan, GC ;Nguyen, TQ "Towards understanding the doping mechanism of organic semiconductors by Lewis acids." Nature materials 18, 12 (2019): 1327-1334. Details. Full text
  • Huang, Z.;Xu, Z.;Mahboub, M ;Liang, Z.;Jaimes, P ;Xia, P.;Graham, KR ;Tang, ML ;Lian, T "Enhanced Near-Infrared-to-Visible Upconversion by Synthetic Control of PbS Nanocrystal Triplet Photosensitizers." Journal of the American Chemical Society 141, 25 (2019): 9769-9772. Details. Full text
  • Fursule, IA ;Abtahi, A ;CB, Watkins ;Graham, KR ;Berron, BJ "In situ crosslinking of surface-initiated ring opening metathesis polymerization of polynorbornene for improved stability." Journal of colloid and interface science 510, (2018): 86-94. Details. Full text
  • Uddin, Md Aslam;Calabro, Rosemary L.;Kim, Doo-Young ;Graham, Kenneth R. "Halide exchange and surface modification of metal halide perovskite nanocrystals with alkyltrichlorosilanes" Nanoscale (2018): Details. Full text
  • Uddin, MA ;Calabro, RL ;Kim, DY ;Graham, KR "Halide exchange and surface modification of metal halide perovskite nanocrystals with alkyltrichlorosilanes." Nanoscale 10, 35 (2018): 16919-16927. Details. Full text
  • Liang, Z.;Graham, KR "Surface Modification of Silver Nanowires for Morphology and Processing Control in Composite Transparent Electrodes." ACS applied materials & interfaces 7, 39 (2015): 21652-6. Details. Full text
* Publications are automatically pulled from based on a user-specific query. Results may include incorrect citations. See: Tutorial on improving PubMed results.