Carlos Silva

• PhD
• Professor (Associate) at Université de Montréal

Two-dimensional metal halide phases, commonly known as 2D perovskites, have emerged as promising materials for exciton polaritons, particularly for polariton condensation. This process entails the spontaneous accumulation of population in the polariton ground state and relies on efficient energy relaxation. In this class of materials, this relaxati...

The lineshapes of spectroscopic transitions offer windows into the local environment of a system. Here, we present a novel approach for connecting the lineshape of a molecular exciton to finite-temperature lattice vibrations. Our results are based upon an exact, self-consistent treatment of a continuous model in which thermal effects are introduced...

It is generally assumed that environmental noise arising from thermal fluctuations is detrimental to preserving coherence and entanglement in a quantum system. In the simplest sense, dephasing and decoherence are tied to energy fluctuations driven by coupling between the system and the normal modes of the bath. Here, we explore the role of noise co...

A versatile technique to measure two-dimensional (2D) coherent electronic spectra involves coherent excitation of a nonlinear optical response and time- and phase-resolved measurement of a resulting population observable, such as photoluminescence intensity, photocurrent, or photoinduced absorption. This coherent spectroscopy is a unique probe in m...

Nonlinear Optical Spectroscopy is a well-developed field with theoretical and experimental advances that have aided multiple fields including chemistry, biology and physics. However, accurate quantum dynamical simulations based on model Hamiltonians are need to interpret the corresponding multi-dimensional spectral signals properly. In this article...

A series of PFDPP copolymers based on fluorene (F) and diketopyrrolopyrrole (DPP) monomers were synthesized via direct arylation polycondensation using Fagnou conditions which involved palladium acetate as catalyst (a gradual catalyst addition of three different percentages were used), potassium carbonate as the base, and neodecanoic acid in N, N-d...

A versatile technique to measure two-dimensional (2D) coherent electronic spectra involves coherent excitation of a nonlinear optical response and time- and phase-resolved measurement of a resulting population observable, such as photoluminescence intensity, photocurrent, or photoinduced absorption. This coherent spectroscopy is a unique probe in m...

Spectral line-shapes provide a window into the local environment coupled to a quantum transition in the condensed phase. In this paper, we build upon a stochastic model to account for non-stationary background processes produced by broad-band pulsed laser stimulation. In particular, we consider the contribution of pair-fluctuations arising from the...

We review our recent quantum stochastic model for spectroscopic lineshapes in the presence of a co-evolving and non-stationary background population of excitations. Starting from a field theory description for interacting bosonic excitons, we derive a reduced model whereby optical excitons are coupled to an incoherent background via scattering as m...

Frenkel excitons are the primary photoexcitations in organic semiconductors and are ultimately responsible for the optical properties of such materials. They are also predicted to form \emph{bound} exciton pairs, termed biexcitons,which are consequential intermediates in a wide range of photophysical processes.Generally, we think of bound states as...

Spectral line-shapes provide a window into the local environment coupled to a quantum transition in the condensed phase. In this paper, we build upon a stochastic model to account for non-stationary background processes produced by broad-band pulsed laser stimulation. In particular, we consider the contribution of pair-fluctuations arising from the...

The lineshape of spectroscopic transitions offer windows into the local environment of a system. Here, we present a novel approach for connecting the lineshape of a molecular exciton to finite-temperature lattice vibrations within the context of the Davydov soliton model (A. S. Davydov and N. I. Kislukha, Phys. Stat. Sol. {\bf 59},465(1973)). Our r...

We review our recent quantum stochastic model for spectroscopic lineshapes in the presence of a coevolving and nonstationary background population of excitations. Starting from a field theory description for interacting bosonic excitons, we derive a reduced model whereby optical excitons are coupled to an incoherent background via scattering as med...

Semiconducting mesocrystalline bulk polymer specimens that exhibit near-intrinsic properties using channel-die pressing are demonstrated. A predominant edge-on orientation is obtained for poly(3-hexylthiophene-2,5-diyl) (P3HT) throughout 2 mm-thick/wide samples. This persistent mesocrystalline arrangement at macroscopic scales allows reliable evalu...

p>We examine the role of surface passivation on carrier trapping and nonlinear recombination dynamics in hybrid metal-halide perovskites by means of excitation correlation photoluminescence (ECPL) spectroscopy. We find that carrier trapping occurs on subnanosecond timescales in both control (unpassivated) and passivated samples, which is consistent...

The commercial feasibility of perovskite solar cells (PSCs) is not guaranteed as long as lead (Pb) is present in the active material, halide perovskites. Mixed halide tin (Sn)-based alloyed perovskites with optimal band gaps ranging from 1.15 to 3.55 eV are excellent alternatives to Pb-based perovskites. In this work, we find that the addition of a...

Frenkel excitons are primary photoexcitations in molecular semiconductors and are unequivocally responsible for their optical properties. However, the spectrum of corresponding biexcitons - bound exciton pairs - has not been resolved thus far in organic materials. We correlate the energy of two-quantum exciton resonances with that of the single-qua...

We examine the role of surface passivation on carrier trapping and nonlinear recombination dynamics in hybrid metal-halide perovskites by means of excitation correlation photoluminescence (ECPL) spectroscopy. We find that carrier...

Experimentally established, non-equilibrium temperature/composition phase diagrams are demonstrated to be useful beyond rationalization of optimum OPV blend composition but also as tools for rapid, qualitative structure–property mapping.

We address the nature of electrochemically induced charged states in conjugated polymers, their evolution as a function of electrochemical potential, and their coupling to their local environment by means of transient absorption and Raman spectroscopies synergistically performed in situ throughout the electrochemical doping process. In particular,...

We develop a stochastic theory that treats time-dependent exciton–exciton s-wave scattering and that accounts for dynamic Coulomb screening, which we describe within a mean-field limit. With this theory, we model excitation-induced dephasing effects on time-resolved two-dimensional coherent optical lineshapes and we identify a number of features th...

The relation of phase morphology and solid‐state microstructure with organic photovoltaic (OPV) device performance has intensely been investigated over the last twenty years. While it has been established that a combination of donor:acceptor intermixing and presence of relatively phase‐pure donor and acceptor domains is needed to get an optimum com...

In this paper, we present a quantum stochastic model for spectroscopic lineshapes in the presence of a co-evolving and non-stationary background population of excitations. Starting from a field theory description for interacting bosonic excitons, we derive a reduced model whereby optical excitons are coupled to an incoherent background via scatteri...

In this work, we address the nature of electrochemically induced charged states in conjugated polymers, their evolution as a function of electrochemical potential, and their coupling to their local environment by means of transient absorption and Raman spectroscopies synergistically performed in situ throughout the electrochemical doping process. I...

In this paper we present a quantum stochastic model for spectroscopic line-shapes in the presence of a co-evolving and non-stationary background population of excitations. Starting from a field theory description for interacting bosonic excitons, we derive a reduced model whereby optical excitons are coupled to an incoherent background via scatteri...

We develop a stochastic scattering theory that quantifies multi-exciton excitation-induced dephasing effects on time-resolved nonlinear coherent optical lineshapes. Our model captures effects of time-dependent exciton-exciton $s$-wave scattering and dynamic Coulomb screening, which we describe within a mean-field limit. The model reveals a number o...

The ever increasing library of materials systems developed for organic solar‐cells, including highly promising non‐fullerene acceptors and new, high‐efficiency donor polymers, demands the development of methodologies that i) allow fast screening of a large number of donor:acceptor combinations prior to device fabrication and ii) permit rapid elucid...

DOI:https://doi.org/10.1103/PhysRevMaterials.4.059901

Quantum entangled photons provide a sensitive probe of many-body interactions and offer a unique experimental portal for quantifying many-body correlations in a material system. In this paper, we present a theoretical demonstration of how photon–photon entanglement can be generated via interactions between coupled qubits. Here, we develop a model f...

The photocatalyst titania film surface acquires a high hydrophilicity after it is exposed to UV light, which is induced by changes in the densities of the surface hydroxyl groups and charge. A xanthene dye, fluorescein, was deposited from a solution onto a titania film after UV irradiation in order to probe the titania surface change. The change in...

We quantify the role of many-body elastic scattering effects on exciton dephasing rates in two-dimensional hybrid metal-halide perovskites by means of nonlinear coherent excitation spectroscopy at a temperature of 5 K. We find that the exciton-density dependence of excitation-induced dephasing (EID) is two to three orders of magnitude lower than in...

It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole tr...

It is still a matter of controversy whether the relative difference in hole and electron transport in solution-processed organic semiconductors is either due to intrinsic properties linked to chemical and solid-state structure or to extrinsic factors, as device architecture. We here isolate the intrinsic factors affecting either electron or hole tr...

Quantum entangled photons provide a sensitive probe of many-body interactions and offer an unique experimental portal for quantifying many-body correlations in a material system. In this paper, we present a theoretical demonstration of how photon-photon entanglement can be generated via interactions between coupled qubits. Here we develop a model f...

Spin-entaglement has been proposed and extensively used in the case of correlated triplet pairs which are intermediate states in singlet fission process in select organic semiconductors. Here, we employ quantum process tomography of polarization entangled photon-pairs resonant with the excited state absorption of these states to investigate the nat...

We report on the exciton formation and relaxation dynamics following photocarrier injection in a single-layer two-dimensional lead-iodide perovskite. We probe the time evolution of four distinct exciton resonances by means of time-resolved photoluminescence and transient absorption spectroscopies, and find that at 5 K a subset of excitons form on a...

We report on the exciton formation and relaxation dynamics following photocarrier injection in a single-layer two-dimensional lead-iodide perovskite. We probe the time evolution of four distinct exciton resonances by means of time-resolved photoluminescence and transient absorption spectroscopies, and find that at 5\,K a subset of excitons form on...

Understanding the structure-property relationships that govern exciton dissociation into polarons in conjugated polymers is key in developing materials for optoelectronic applications such as light-emitting diodes and solar cells. Here, the polymer poly(9,9-dioctylfluorene) (PFO), which can form a minority population of chain segments in a distinct...

Recent theories and experiments have explored the use of entangled photons as a spectroscopic probe of physical systems. We describe here a theoretical description for entropy production in the scattering of an entangled biphoton Fock state within an optical cavity. We develop this using perturbation theory by expanding the biphoton scattering matr...

In two-dimensional hybrid organic-inorganic metal-halide perovskites, the intrinsic optical excitation lineshape reflects multiple excitons with distinct binding energies, which are dressed differently by the hybrid lattice. Given this complexity, a fundamentally far-reaching issue is how Coulomb-mediated many-body interactions --- elastic scatteri...

Hybrid organic–inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the...

In the version of this Article originally published, the units of the Fig. 3a x axis were incorrectly given as meV. They should have been eV. This has now been corrected in all versions of the Article.

(4NPEA) 2 PbI 4 (4NPEA = 4-nitrophenylethylammonium) is the first 3 × 3 corrugated 2D organic-Pb/I perovskite. The nitro groups are involved in cation-cation and cation-iodide interactions. The structure contains both highly distorted and near-ideal PbI 6 octahedra, consistent with the observation of two ²⁰⁷ Pb NMR resonances, while the optical pro...

Although stretchable polymer-based devices with promising electrical performance have been produced through the polymer blend strategy, the interplay between the blend film microstructure and macroscopic device performance under deformation has yet to be unambiguously articulated. Here, we discuss the formation of robust semiconducting networks in...

By means of non-resonant Raman spectroscopy and density functional theory calculations, we measure and assign the vibrational spectrum of two distinct two-dimensional lead-iodide perovskite derivatives. These two samples are selected in order to probe the effects of the organic cation on lattice dynamics. One templating cation is composed of a phen...

Conjugated monomers and polymers containing 2,2′-bithiazole (BTz) and naphthalene diimide (NDI) units in the main chain were prepared. Polymer PNDI2Tz was obtained via palladium-catalyzed Stille polycondensation of a dibromo-substituted NDI derivative with distannyl-2,2′-bithiazole. The optical and electronic properties were investigated using UV–v...

Hybrid organic/inorganic semiconductors feature complex lattice dynamics due to the `softness' arising from non-covalent bonds between molecular moieties and the inorganic network, and due to the ionic character of the crystal. Such complex lattice motion has profound consequences on the fundamental character of primary photoexcitations with respec...

Recent theoretical and experiments have explored the use of entangled photons as a spectroscopic probe of material systems. We develop here a theoretical description for entropy production in the scattering of an entangled biphoton state within an optical cavity. We develop this using perturbation theory by expanding the biphoton scattering matrix...

Owing to both electronic and dielectric confinement effects, two-dimensional organic-inorganic hybrid perovskites sustain strongly bound excitons at room temperature. Here, we demonstrate that there are non-negligible contributions to the excitonic correlations that are specific to the lattice structure and its polar fluctuations, both of which are...

With strongly bound and stable excitons at room temperature, single-layer, two-dimensional organic-inorganic hybrid perovskites are viable semiconductors for light-emitting quantum optoelectronics applications. In such a technological context, it is imperative to comprehensively explore all the factors --- chemical, electronic and structural --- th...

With strongly bound and stable excitons at room temperature, single-layer, two-dimensional organic-inorganic hybrid perovskites are viable semiconductors for light-emitting quantum optoelectronics applications. In such a technological context, it is imperative to comprehensively explore all the factors --- chemical, electronic and structural --- th...

Many typical organic optoelectronic devices, such as light-emitting diodes, field-effect transistors, and photovoltaic cells, use an ultrathin active layer where the organic semiconductor is confined within nanoscale dimensions. However, the question of how this spatial constraint impacts the active material is rarely addressed, although it may hav...

We present an input/output analysis of photon-correlation experiments whereby a quantum mechanically entangled bi-photon state interacts with a material sample placed in one arm of a Hong-Ou-Mandel (HOM) apparatus. We show that the output signal contains detailed information about subsequent entanglement with the microscopic quantum states in the s...

We present theoretical and experimental results showing the effects of incoherent population mixing on two-dimensional (2D) coherent excitation spectra that are measured via a time-integrated population and phase-sensitive detection. The technique uses four collinear ultrashort pulses and phase modulation to acquire two-dimensional spectra by isola...

We measure the homogeneous excitation linewidth of regioregular poly(3-hexylthiophene), a model semicrystalline polymeric semiconductor, by means of two-dimensional coherent photoluminescence excitation spectroscopy. At a temperature of 8\,K, we find a linewidth that is always $\gtrsim 110$\,meV full-width-at-half-maximum, which is a significant fr...

The optical properties of a series of strongly coupled microcavities containing the fluorescent molecular dye BODIPY-Br (bromine-substituted boron-dipyrromethene) dispersed into a transparent dielectric matrix are explored, with each cavity having a different exciton–photon detuning. Using temperature dependent emission, time-resolved spectroscopy,...

While ultrafast spectroscopy with photocurrent detection was almost unknown before 2012, in the last three years a number of research groups from different fields have independently developed ultrafast electric probe approaches and reported promising pilot studies. Here we discuss these recent advances and provide our perspective on how photocurren...

In high-performance solar cells based on polymeric semiconductors, the mechanism of photocarrier generation on $<100$-fs timescales is yet to be unravelled. In particular the dynamics of early-time electronic coupling between excitons on polymer chains and charge-transfer states need to be investigated in order to develop a detailed picture of ultr...

Blends of alternating ‘push–pull’ donor/acceptor (d/a) co-polymers with soluble fullerenes as active materials have shown promise for increasing power conversion efficiencies in organic photovoltaic (OPV) devices. We investigate morphology-dependent optical and electronic properties of poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dit...

In this work, we investigate the effect of phase morphology on the nature of charges in poly(2,5-bis(3-tetradecyl-thiophen-2-yl)thieno[3,2,-b]thiophene) (pBTTT-C16) and phenyl-C61-butyric acid methyl ester (PC61BM) blends over timescales greater than hundreds of microseconds by quasi-steady-state photoinduced absorption spectroscopy. Specifically,...

DOI:https://doi.org/10.1103/PhysRevB.91.079901

Dye-sensitized metal oxide polymer hybrid solar cells deliver a promising basis in organic solar cell development due to many conceptual advantages. Since the power conversion efficiency is still in a noncompetitive state, it has to be understood how the photocurrent contribution can be maximized (i.e., which dye-polymer properties are most benefic...

We demonstrate an enhancement of photocurrent in hybrid photovoltaic cells based on nanoparticles of zinc oxide (ZnO) and poly(3-hexylthiophene) (P3HT), through molecular interface modification with and without cis-bis(4,4′-dicarboxy-2,2′bipyridine) ruthenium (II) (N3-dye) and α-Sexithiophen-2-yl-phosphonic Acid (6TP) as interface modifiers. We ide...

Here we report on an exciton/lattice model of the electronic dynamics of primary photo excitations in a polymeric semiconductor heterojunction that includes both polymer π-stacking, energetic disorder and phonon relaxation. Our model indicates that that in polymer/fulerene heterojunction systems, resonant tunnelling processes brought about by envir...

Aggregates of conjugated polymers exhibit two classes of fundamental electronic interactions: those occurring within a given chain and those occurring between chains. The impact of such excitonic interactions on the photophysics of polymer films can be understood using concepts of J- and H-aggregation originally developed by Kasha and coworkers to...

In polymeric semiconductors, charge carriers are polarons, which means that the excess charge deforms the molecular structure of the polymer chain that hosts it. This effect results in distinctive signatures in the vibrational modes of the polymer. We probe polaron photo- generation dynamics at polymer:fullerene heterojunctions by monitoring its ti...

The optoelectronic properties of macromolecular semiconductors depend fundamentally on their solid-state microstructure. For example, the molecular-weight distribution influences polymeric- semiconductor properties via diverse microstructures; polymers of low weight-average molecular weight (Mw) form unconnected, extended-chain crystals, usually of...

We present an exciton/lattice model of the electronic dynamics of primary photoexcitations in a polymeric semiconductor heterojunction which includes both polymer pi-stacking, energetic disorder, and phonon relaxation. Results from our model are consistent with a wide range of recent experimental evidence that excitons decay directly to well-define...

In this study, a generally applicable strategy is described to manipulate the optical properties of a wide range of polymer semiconductors in the solid state. Blending these materials with a non-conjugated, polar polymer matrix is found to be the processing key to a drastic change and red-shift of the absorption characteristics.

In this work, we study the nature of long-lived photoexcitations in intercalated, partially and predominantly non-intercalated semicrystalline poly(2,5-bis(3-tetradecyl-thiophen-2-yl)thieno [3,2,-b]thiophene) (pBTTT):phenyl-C61 -butyric acid methyl ester (PC61BM) blend films by quasi-steady-state photoinduced absorption (PIA) spectroscopy. We find...

We investigate how the acceptor-rich domain influences the microstructure and photoluminescence properties, and consequently the external quantum efficiency of photovoltaic diodes based on blend films of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N'-diphenyl)-N,N'di(p-butyl-oxy-pheyl)-1,4-diaminobenzene)] (PFB) and poly[9,9-dioctylfluorenyl-2,7-diy...

Electronic properties of organic semiconductors are often critically dependent upon their ability to order from the molecular level to the macro-scale, as is true for many other materials attributes of macromolecular matter such as mechanical characteristics. Therefore, understanding of the molecular assembly process and the resulting solid-state s...

The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer chemical nature and molecular weight. Specifically, low-molecular-weight materials form crystalline domains of cofacially $\p...

We find that the external quantum efficiency of photovoltaic diodes based on finely mixed blends of poly-9,9’-dioctylfluorene-co-bis-N,N’-(4-butylphenyl)-bis-N,N’-phenyl-l,4-phenylenediamine (PFB) and poly-9,9’- dioctylfluorene-co-benzothiadiazole (F8BT) depends strongly on the blend ratio. The peak external quantum efficiency is optimum for a PFB:...

Excitation of organic donor-acceptor systems with high-energy light can produce hot charge-transfer states that are delocalized across the heterojunction and readily dissociate. Two studies now reveal the dynamics of this process and pave the way towards unravelling the details of the molecular landscape that favours fast photocarrier generation.

We investigate the properties of long-lived species, such as geminate electron-hole pairs, in F8BT films through time-resolved photoluminescence (PL) measurements at room temperature and 10 K. The kinetics consist of an initial exponential decay τ = 2.26 ns) followed by a weak power-law decay (I(t) ∝ t(-1)) up to at least 1 ms, both of which depend...

We explore charge recombination dynamics at electron donor-acceptor heterojunctions, formed between a semiconductor polymer (PCDTBT) and a fullerene derivative (PC70BM), by means of combined time-resolved photoluminescence and transient absorption spectroscopies. Following prompt exciton dissociation across the heterojunction, a subset of bound ele...

Polymeric semiconductors such has regioregular poly(3-hexylthiophene) have electronic proprieties that can be tuned by proper control of the solid-state microstructure. We process thin films of P3HT of different molecular weight ranging from 2 kg/mol to 341 kg/mol. The polymer undergo a transition from a paraffinic, non-entangled microstructure to...

We examine the interdependence of structural and electronic properties of two substituted pyrene crystals by means of combined spectroscopic probes and density-functional theory calculations. Substituted pyrenes are useful model systems to unravel the interplay of crystal structure and electronic properties in organic semiconductors. To study the e...

We present a reaction/diffusion model for the formation of a lower polariton condensate in a micro cavity containing an organic semiconducting molecular crystalline film. Our model--based upon an anthracene film sandwiched between two reflecting dielectric mirrors--consists of three coupled fields corresponding to a gas of excitons created by an ex...

We consider here the thermodynamics and phase-diagram of exciton/polaritons formed in low-dimensional organic single-crystal microcavities. Using the Dicke model for a lattice of Frenkel excitons coupled to a common cavity mode, we explore the transition between normal and condensate regimes as depending upon the exciton band-width and temperature...

Organic photovoltaic devices are presently the subject of intense research since they could eventually propose solar energy solutions at a much reduced cost compared to inorganic devices. Presently, electron transport in organic photovoltaic devices is achieved with a fullerene derivative (PCBM) but this solution has some disadvantages. First, the...

We examine the possibility of observing Bose condensation of a confined two-dimensional polariton gas in an organic quantum well. We deduce a suitable parameterization of a model polynomial Hamiltonian based upon the cavity geometry, the biexciton binding energy, and similar spectroscopic and structural data. By converting the sum-over-states to a...

The influence of solid-state microstructure on the optoelectronic properties of conjugated polymers is widely recognized, but still poorly understood. Here, we show how the microstructure of conjugated polymers controls the yield and decay dynamics of long-lived photogenerated charge in neat films. Poly(3-hexylthiophene) was used as a model system....

In organic photovoltaic diodes, singlet intrachain excitons dissociate into geminate polaron pairs (GPP) at the heterojonction, which further dissociate into photocarriers or relax into charge transfer exciton (CTX) states. Our temperature-dependent, time-resolved spectroscopic approach unravels the dynamics of those species in films of polycarbazo...