Research

The Luping Yu research group carries out interdisciplinary research with special focus on the area between chemistry and materials science.  We are developing new synthetic approaches for the synthesis of functional polymers and molecular electronic components, and exploring new surface reactivity and supramolecular chemistry for self-assembly of nanostructured materials. Our overarching philosophy is the exploration of the relationships between chemical structure and resulting properties so as to facilitate discovery of new materials for organic solar cells, organic electronics, water splitting, and other practical applications. 

Light harvesting materials

The sun is the largest energy source available to human society, as well as being renewable and clean. Organic photovoltaic (OPV) solar cells are attractive both because of fundamental scientific challenges in understanding how to manipulate charge transport and exciton dynamics in devices, along with their enormous technological promise in offering solar energy harvesting devices that are light weight, flexible, easily deployable, and low-cost. In our group we are developing state of art materials for both fundamental studies and device optimization. Both new electron donor and acceptor materials are designed and synthesized for use in bulk heterojunction OPV devices. Extensive effort is devoted to the characterization of these new materials with regard to their structural and photophysical properties. [1-3] In addition to designing functional materials, approaches to optimizing light conversion are pursued through device engineering and the optimization of processing conditions, including plasmonic enhancement of light absorption [4], nanotubes for increased charge transport [5], and ternary blend solar cells [6-8]. 

Currently, most successful bulk heterojunction organic solar cells are fabricated with polymer or small molecule donor and fullerene-derived acceptor. However, fullerene-based materials have known disadvantages, such as high cost and difficulty of modification. We are developing new acceptor materials in order to replace fullerene. Considering the dominance of fullerenes in OPV devices, this work also requires us to pursue completely new design principles for electron acceptors. [9-10] 

In addition to photovoltaics, one approach to convert sunlight into usable forms of energy, is to utilize solar energy to photo-catalytically convert inert chemicals, such as water and carbon dioxide, into energy-rich, storable chemical fuels. Light-induced splitting of water into oxygen and hydrogen is the most attractive approach not only because it can provide one potential solution to the world’s ever-increasing energy demands, but also because the resulting fuel is environmentally benign. Our method toward this goal is the development of photocatalysts based on semiconducting polymers chelated with transition metal complexes. Preliminary results have validated this strategy by demonstrating hydrogen evolution from water.  We are systematically investigating the nature of the catalytically active sites in order to further improve the quantum efficiency in these organic systems for water splitting. 

Materials for applications in molecular electronics

Charge transport through single molecules is an active research topic worldwide. Different molecular components, including molecular wires and diode molecules, are being synthesized and investigated.  In this field, both measurements and theoretical computations of charge transport phenomena have led to a deep understanding of this topic.  Despite this progress, the ability to control charge transport through single molecules is still a challenging, unanswered problem. Understanding how current passes through molecules is important for enabling advanced molecular circuitry. 

We are interested in methods for control of charge transport through single molecules and actively developing molecular p-n junctions and molecular transistors. Our experience in this field goes back a decade since 2002 when we synthesized the first molecular p-n junctions [11] .  

More recently we demonstrated edge-on chemical gating effect in molecular wires utilizing the pyridinoparacyclophane moiety as the gate. The results show behavior similar to  field-effect transistors. [12] 

Molecular wire

In addition, we reported an on/off switch based on the same molecular wire system containing the same edge-on pyridinoparacyclophane moiety, triggered by the protonation of the pyridine ring. The results reveal that the protonation/ deprotonation processes on the nitrogen atom of the edge-on pyridine ring can reversibly alter the electrical properties of the molecular wire, leading to a binary system. Detailed studies on structure-property relationship are in progress.  

Previous research projects


Selected publications:

[1]      Y. Liang and L. Yu, “A New Class of Semiconducting Polymers for Bulk Heterojunction Solar Cells with Exceptionally High Performance,” Acc. Chem. Res., vol. 43, no. 9, pp. 1227–1236, 2010.

[2]      B. Carsten, J. M. Szarko, H. J. Son, W. Wang, L. Lu, F. He, B. S. Rolczynski, S. J. Lou, L. X. Chen, and L. Yu, “Examining the effect of the dipole moment on charge separation in donor-acceptor polymers for organic photovoltaic applications.,” J. Am. Chem. Soc., vol. 133, no. 50, pp. 20468–75, 2011.

[3]      B. S. Rolczynski, J. M. Szarko, H. J. Son, L. Yu, and L. X. Chen, “Effects of Exciton Polarity in Charge-Transfer Polymer/PCBM Bulk Heterojunction Films,” J. Phys. Chem. Lett., vol. 5, no. 11, pp. 1856–1863, 2014.

[4]      L. Lu, Z. Luo, T. Xu, and L. Yu, “Cooperative Plasmonic Effect of Ag and Au Nanoparticles on Enhancing Performance of Polymer Solar Cells,” Nano Lett., vol. 13, no. 1, pp. 59–64, 2013.

[5]      L. Lu, T. Xu, W. Chen, J. M. Lee, Z. Luo, I. H. Jung, H. Il Park, S. O. Kim, and L. Yu, “The role of N-doped multiwall carbon nanotubes in achieving highly efficient polymer bulk heterojunction solar cells,” Nano Lett., vol. 13, no. 6, pp. 2365–2369, 2013.

[6]      L. Lu, T. Xu, W. Chen, E. S. Landry, and L. Yu, “Ternary blend polymer solar cells with enhanced power conversion efficiency,” Nat. Photonics, vol. 8, no. 9, pp. 716–722, 2014.

[7]      L. Lu, W. Chen, T. Xu, and L. Yu, “High-performance ternary blend polymer solar cells involving both energy transfer and hole relay processes.,” Nat. Commun., vol. 6, p. 7327, 2015.

[8]      L. Lu, M. A. Kelly, W. You, and L. Yu, “Status and prospects for ternary organic photovoltaics,” Nat. Photonics, vol. 9, no. 8, pp. 491–500, 2015.

[9]      I. H. Jung, W.-Y. Lo, J. Jang, W. Chen, D. Zhao, E. S. Landry, L. Lu, D. V Talapin, and L. Yu, “Synthesis and Search for Design Principles of New Electron Accepting Polymers for All-Polymer Solar Cells,” Chem. Mater., vol. 26, no. 11, pp. 3450–3459, 2014.

[10]    I. H. Jung, D. Zhao, J. Jang, W. Chen, E. S. Landry, L. Lu, D. V. Talapin, and L. Yu, “Development and Structure/Property Relationship of New Electron Accepting Polymers Based on Thieno[2′,3′:4,5]pyrido[2,3- g ]thieno[3,2- c ]quinoline-4,10-dione for All-Polymer Solar Cells,” Chem. Mater., vol. 27, no. 17, pp. 5941–5948, 2015.

[11]     Ng, M. K.; Yu, L. Synthesis of Amphiphilic Conjugated Diblock Oligomers as Molecular Diodes. Angew. Chemie, vol. 114, no.19, pp 3750–3753, 2002.

[12]    W.-Y. Lo, W. Bi, L. Li, I. H. Jung, and L. Yu, “Edge-on gating effect in molecular wires.,” Nano Lett., vol. 15, no. 2, pp. 958–62, 2015.