About

Tianquan “Tim” Lian is the John H. and Margaret B. Fassitt Professor of Chemistry at the University of Pennsylvania. He serves as the Editor-in-Chief of The Journal of Chemical Physics. Professor Lian's research focuses on several key areas within chemistry, including Chemical Physics and Physical Chemistry, Energy Research, Laser Chemistry and Spectroscopy, Materials Chemistry, and Nanoscale Science and Engineering. His work spans fundamental and applied aspects of these fields, contributing to the understanding and advancement of chemical processes at the molecular and nanoscale levels. Professor Lian is based in VLEST 528 and can be contacted via email at tlian@sas.upenn.edu or by phone at 215-746-2354.

Research topics

• Optoelectronics
• Physics
• Chemistry
• Materials science
• Chemical engineering
• Chemical physics
• Physical chemistry
• Nanotechnology
• Photochemistry
• Thermodynamics
• Quantum mechanics
• Organic chemistry
• Atomic physics
• Computational chemistry

Selected publications

• Impact of Cation Insertion on Semiconducting Polymer Thin Films toward Electrochemical Energy Conversion

  Chemistry of Materials · 2026-01-08

  article

  Semiconducting polymers are being explored for electrochemical and photoelectrochemical energy transformation and storage applications. For these applications, it is critical to understand how ion insertion from the electrolyte into polymer electrodes modulates the polymer electronic structure and electron doping levels. This study explores electrochemical cation insertion in the n-type conjugated redox polymer P90, composed of alternating naphthalene diimide (NDI) acceptor and bithiophene (T2) donor units, where the NDI units are functionalized with heptaethylene glycol (HEG, 90%) and 2-octyl dodecyl (OD, 10%) side chains. By combining in situ techniques (UV–vis absorption and Raman spectroscopies with electrochemistry), structural analysis using ex situ grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) calculations, we reveal that dications enable negative polaron and bipolaron formation in the P90 at less reducing potentials while supporting more bipolaron formation than the monocations; moreover, larger dications with smaller hydrated radii increase the maximum P90 electron doping level. We also determine that the monocations lead to more thermodynamically stabilized polarons compared with the dications. These findings highlight the critical role of cation identity in tuning electrochemical charging, charge stabilization, and electronic structure of n-type conjugated redox polymers, providing guidance on the rational design of polymer-based (photo)electrochemical applications.

  PublisherDOI

• Eliminated Interfacial Side Reactions in Perovskite Solar Cells by Sterically Protected Ammonium Passivation

  ACS Applied Materials & Interfaces · 2026-04-22

  article

  Surface passivation utilization of ammonium salts has emerged as an effective strategy to reduce interfacial defects at the surface and improve device performance. However, ammonium salts are prone to deprotonation under high temperature, which can induce side reactions with organic cations (FA+ and MA+) at the perovskite surface and further influence the device stability. Herein, we systematically investigate the passivation effects of cyclohexylammonium iodide (CHAI), methylcyclohexylammonium iodide (MCHAI), and N,N-dimethylcyclohexylammonium iodide (DMCHAI) on PSCs. DMCHAI exhibits a significantly suppressed deprotonation tendency due to the sterically hindered ammonium group, effectively inhibiting the reaction with FA+ at the interface. As a result, the champion device with DMCHAI modification achieves a PCE of 26.06% with Voc of 1.20 V and retains over 98% of the initial PCE after 7200 h under N2. Moreover, the device with DMCHAI modification remains over 86% of its initial efficiency after 550 h of thermal stress at 85 °C. This work highlights the importance of deprotonation-resistant ammonium salts in constructing thermally stable perovskite interfaces and provides a rational design guideline for passivation materials in PSCs.

  PublisherDOI

• Excited State Dynamics of CO ₂ Reduction Catalyst under Vibrational Strong Coupling

  Journal of the American Chemical Society · 2025-10-10 · 2 citations

  articleOpen accessSenior authorCorresponding

  Molecular polaritons, formed by coupling molecular electronic or vibrational transitions to photonic modes in microcavities, have gained interest for their potential to influence chemical dynamics. Here, we investigate the effects of vibrational strong coupling (VSC) on solvation-induced time-dependent Stokes shifts using transient infrared (IR) transmission spectroscopy. The electronic excited-state dynamics of the Re(bpy-COOH)(CO)3Cl complex (ReC0A) is monitored via angle-resolved time-dependent transmission spectra of vibrational polaritons following 400 nm excitation inside a Fabry–Perot cavity. Our results reveal distinct infrared polaritonic signatures of the CO dynamical Stokes shift, which we interpret using simulations based on a time-dependent excited-state absorption model. We observed negligible change of the solvation-induced vibrational dynamic Stokes shift of the CO modes under VSC. We also investigate the perturbed free induction decay in the cavity and its connection to polariton dynamics. This setup allows us to probe and test potential fundamental VSC effects on molecular processes relevant to the reactivity and charge transfer.

  PublisherDOI

• Fano Resonance in CO₂ Reduction Catalyst Functionalized Quantum Dots

  Journal of the American Chemical Society · 2025-03-21 · 12 citations

  articleOpen accessSenior authorCorresponding

  Molecular catalyst functionalized semiconductor quantum dots (QDs) are a promising modular platform for developing novel hybrid photocatalysts. The interaction between adsorbed catalyst vibrations and the QD electron intraband absorption can influence the photophysical properties of both the QD and the catalysts and potentially their photocatalysis. In CdSe QDs functionalized by the CO2 reduction catalyst, Re(CO)3(4,4’-bipyridine-COOH)Cl, we observe that the transient Fano resonance signal resulting from coupling of the catalyst CO stretching mode and the QD conduction band electron mid-IR intraband absorption appears on an ultrafast time scale and decays with the electron population, irrespective of the occurrence of photoreduced catalysts. The Fano asymmetry factor increases with an increase in the adsorbed catalyst number and a decrease in QD sizes. The latter can be attributed to an enhanced charge transfer interaction between the more strongly quantum-confined QD conduction band and catalyst LUMO levels. These results provide a more in-depth understanding of interactions in excited QD-catalyst hybrid photocatalysts.

  PublisherOA PDFDOI

• Photodriven water oxidation initiated by a surface bound chromophore-donor-catalyst assembly

  UNC Libraries · 2025-10-30

  articleOpen accessSenior author

  In photosynthesis, solar energy is used to produce solar fuels in the form of new chemical bonds. A critical step to mimic photosystem II (PS II), a key protein in nature's photosynthesis, for artificial photosynthesis is designing devices for efficient light-driven water oxidation. Here, we describe a single molecular assembly electrode that duplicates the key components of PSII. It consists of a polypyridyl light absorber, chemically linked to an intermediate electron donor, with a molecular-based water oxidation catalyst on a SnO₂/TiO₂ core/shell electrode. The synthetic device mimics PSII in achieving sustained, light-driven water oxidation catalysis. It highlights the value of the tyrosine-histidine pair in PSII in achieving efficient water oxidation catalysis in artificial photosynthetic devices.

  PublisherDOI

• Effective Selection and Targeted Passivation for Different Defect Types by Ammonium Salts in Perovskite Solar Cells

  Advanced Energy Materials · 2025-09-03 · 6 citations

  article

  Abstract The optimal selection of alkyl chains and halogen ions in ammonium salts for addressing specific defect types in perovskite films remains unclear, although ammonium salts emerged as a promising strategy to enhance the performance of perovskite solar cells (PSCs). Herein, four ammonium salts are introduced with different alkyl chain types and halogen ions to passivate perovskite films. Branched‐alkyl chain ammonium salts exhibited superior passivation effects compared to linear‐alkyl chain salts, with the alkyl chain structure having a more significant impact on device performance than the halogen ion component. In addition, DFT calculations are performed to investigate which defect types in perovskite films are most effectively passivated by different alkyl chain types and halogen ions in ammonium salts. Branched‐alkyl chain ammonium salts demonstrated superior passivation effects on V Pb and V FA defects in perovskite films compared to linear‐alkyl chain salts, while exhibiting similar passivation effects for V I defects. PSCs passivated with tert‐OAI achieved an impressive efficiency of 25.49%, with a V oc of 1.19 V, a J sc of 25.40 mA cm − 2 , and an FF of 84.34%. This work highlights a targeted ammonium salt passivation strategy tailored to address different defect types in perovskite films, accounting for variations in perovskite composition and fabrication environments.

  PublisherDOI

• <i>Operando</i> Contactless EFISH Study of the Rate-Determining Step of Light-Driven Water Oxidation on TiO₂ Photoanodes

  Journal of the American Chemical Society · 2025-05-21 · 3 citations

  articleOpen accessSenior authorCorresponding

  For many slow solar-fuel-forming reactions, the accumulation of photogenerated minority carriers on the photoelectrode surface leads to light-induced band edge unpinning, affecting the junction properties by decreasing band bending in the semiconductor space charge layer and increasing the driving force of surface reactions in the electric double layer. In this study, we demonstrate a contactless operando electric field-induced second harmonic generation (EFISH) method for measuring the band bending change (δΔΦSCRL) on photoelectrodes upon photoexcitation. For n-doped rutile TiO2 water oxidation photoanodes at pH 7, δΔΦSCRL increases at more positive potentials or higher illumination power density until it reaches saturation values. We show that under fast mass transport conditions, δΔΦSCRL is exclusively attributed to the accumulated charged rate-determining species that can be regarded as temporary surface states, and the relationship between the photocurrent and δΔΦSCRL can be well modeled by assuming that hole trap states function as the reaction center. Kinetic isotope experiments identify proton-coupled electron transfer as the rate-determining step and suggest a possible chemical nature of the key intermediate. We demonstrate that light-induced band edge unpinning is a beneficial feature under high illumination conditions for oxygen evolution reaction on TiO2 because it maintains the photon-to-current conversion efficiency by enhancing the surface reaction driving force, shedding light on the actual device application.

  PublisherDOI

• Illuminating the mechanistic impacts of an Fe-quaterpyridine functionalized crystalline poly(triazine imide) semiconductor for photocatalytic CO ₂ reduction

  Inorganic Chemistry Frontiers · 2025-01-01 · 2 citations

  articleOpen access

  Attachment of a Fe-quaterpyridine catalyst to carbon nitride produces a photocatalyst that selectively reduces CO 2 to CO in water.

  PublisherOA PDFDOI

• Electron Transfer Energetics in Photoelectrochemical CO₂ Reduction at Viologen Redox Polymer-Modified p-Si Electrodes

  Journal of the American Chemical Society · 2025-03-06 · 7 citations

  articleCorresponding

  While redox polymer-mediated catalysis at silicon photoelectrodes has been studied since the 1980s, there have been few detailed studies of these materials in photoelectrochemical CO2 reduction. Here, we develop silicon photoelectrodes functionalized with a viologen-based polymer that mediates the formation of catalytic gold nanoparticles. The presence of gold was confirmed by X-ray photoelectron spectroscopy (XPS), and the nanoparticles were imaged with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). We probed the CO2 reduction process during bulk photoelectrolysis to find modest, yet consistent CO faradaic efficiencies across a range of applied potentials. Operando surface-enhanced Raman spectroscopy (SERS) was used to measure the Fermi levels of both the viologen polymer and the Au catalyst sites. The operando measurement of the Fermi levels of all three components of the photocathode provides a unified picture of the electron transfer process in the semiconductor-redox polymer–catalyst system. The redox polymer serves as the electron transfer mediator between the Si substrate and Au sites. In addition, the Au Fermi level equilibrates with the Fermi level of the viologen polymer, which in turn fixes the quasi-Fermi level of Au catalysts at the p-Si/redox polymer interface. This suggests a potential future direction of using redox polymers with tunable potentials to modulate the potential of metal cocatalysts and thus control the reaction selectivity.

  PublisherDOI

• Control of Reversible Oxidative Addition/Reductive Elimination of Surface-Attached Catalysts by External Electric Fields

  The Journal of Physical Chemistry Letters · 2025-03-11 · 3 citations

  article

  We demonstrate that applied electric fields at interfaces can control the oxidative addition/reductive elimination equilibria of surface-attached molecular catalysts without any synthetic modification. Density functional theory (DFT) calculations show that the oxidative addition of HCl to a Co complex is “field switchable”, being favorable under negative fields but unfavorable under sufficiently positive fields. Extending the analysis to different substrates (O2, H2) and metal centers (Rh, Ir) reveals consistent trends in the magnitude of the electric field effect: Co > Rh ≈ Ir and HCl > O2 > H2. Our analysis indicates that these field-dependent effects are driven by changes in the permanent dipole moment, offering key insights for the design of field-controllable catalytic systems. This framework presents a novel strategy to overcome the “Goldilocks problem” of balancing competing catalytic steps by leveraging applied electric fields to dynamically tune catalytic reactivity in situ.

  PublisherDOI

Recent grants

• Polariton and CISS Effects on Photoinduced Electron Transfer from Quantum Confined Semiconductor Nanocrystals

  NSF · $520k · 2023–2026

• Imaging charge transfer dynamics in nanomaterials using electron donor/acceptor modified AFM tips

  NSF · $195k · 2012–2014

• Multi-Exciton Dissociation in Quantum Dots by Ultrafast Charge Transfer to Adsorbates

  NSF · $408k · 2009–2012

• Mechanisms of Triple Energy Transfer and Polaron Formation in Nanocrystals

  NSF · $618k · 2020–2023

• Probing Charge Transfer Dynamics in Single QD-Molecule Complexes Using QD or Molecule Modified AFM Tips

  NSF · $420k · 2013–2016

Frequent coauthors

• Djamaladdin G. Musaev

  Atlanta University Center

  229 shared

• Craig L. Hill

  Emory University

  194 shared

• Alexey L. Kaledin

  Atlanta University Center

  135 shared

• Yurii V. Geletii

  Emory University

  89 shared

• Zhuangqun Huang

  Bruker (United States)

  82 shared

• Kaifeng Wu

  Chinese Academy of Sciences

  58 shared

• Zihao Xu

  Grinm Advanced Materials (China)

  58 shared

• Jianchang Guo

  Argonne National Laboratory

  51 shared