Vincenzo Lordi | Lawrence Livermore National Lab (original) (raw)

Papers by Vincenzo Lordi

Applied Physics Letters

Hydrogen-doped In2O3 synthesized using magnetron sputtering or atomic layer deposition in the pre... more Hydrogen-doped In2O3 synthesized using magnetron sputtering or atomic layer deposition in the presence of water vapor has high transparency in the near infra-red region and mobility values that are almost three to four times of those in commercially used In2O3:Sn at a much lower carrier concentration. However, simple questions like what happens when water molecules enter In2O3 or why the dominant charge carrier changes from an oxygen vacancy in In2O3:Sn to H+ in In2O3 are not clear. Using hybrid functional based density functional theory calculations, we show that water molecules spontaneously split into H+ and OH−. The H+ interstitial bonds with an oxygen in In2O3, and the OH− interstitial occupies a vacant lattice site or is trapped by an oxygen vacancy. Thus, in agreement with experimental findings, our results suggest that the concentration of oxygen vacancies decreases as the partial pressure of water increases. The charge transition level, ϵ(−/+), of a hydrogen interstitial an...

2020 47th IEEE Photovoltaic Specialists Conference (PVSC)

Nine types of CIGS cells were studied with permutations of sodium content, buffer type (CdS or Zn... more Nine types of CIGS cells were studied with permutations of sodium content, buffer type (CdS or Zn(O, S)), and post-deposition treatment (PDT) with KF, RbF, or oxidation. JV, QE, and CV measurements are presented for several cells of each type. KF PDT with CdS buffer resulted in the highest efficiency. Although Zn(O, S) buffer cells with typical sodium content had relatively low efficiency, RbF PDT significantly improved performance. Oxidation alone significantly increased the efficiency of sodium deficient cells with CdS buffer. Numerical modeling was conducted to connect device properties to the observed performance variations.

2020 47th IEEE Photovoltaic Specialists Conference (PVSC), 2020

Three types of CIGS devices with varying treatments of RbF post-deposition treatment (PDT) and so... more Three types of CIGS devices with varying treatments of RbF post-deposition treatment (PDT) and sodium are subjected to accelerated stress test (AST) conditions at elevated temperature (65 °C), voltage bias (short- vs open-circuit), and illumination (AM1.5 vs dark). RbF treatment with reduced CdS thickness shows an improvement in Voc and efficiency in this sample series, and also results in high FF and doping ~ 1016cm−3. Cells with reduced sodium show a decrease in Voc and infrared QE results suggest a higher optical minimum bandgap. Heat and light soaking experiments at 50, 65, and 75 °C, open and short-circuit junction bias under AM1.5G illumination suggest stabilization of CIGS solar cells with addition of Na and RbF. SCAPS-1D simulations suggest reduction in thermally ionized defect density in ordered vacancy compound (OVC) and changes in conduction band offset with RbF post-deposition treatment. Further, simulations show an increase in shallow acceptor and donor density after open-circuit and short-circuit AST respectively. Preliminary light soaking results for oxidized CIGS with and without Na are also discussed.

2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC), 2018

Three types of CIGS cells were fabricated: 1) with CdS buffer; 2) with CdS buffer and limited sod... more Three types of CIGS cells were fabricated: 1) with CdS buffer; 2) with CdS buffer and limited sodium; and 3) with Zn(O,S) buffer. Baseline numerical models were developed with compositional grading based on GDOES data. Calculations were compared to W, QE, and CV measurements. Cells with lower sodium content exhibited higher gallium content and poor performance due to increased recombination. Similar but slightly lower efficiencies were observed for Zn(O,S) buffer cells compared CdS buffer cells. Results indicate that a highly doped p-type layer near the CIGS /buffer interface and graded defect profiles play important roles in accounting for the data.

Bulletin of the American Physical Society, 2017

ECS Meeting Abstracts, 2021

The Journal of Physical Chemistry C, 2020

Journal of Applied Physics, 2020

New Journal of Physics, 2019

In order to realize the full potential of ion trap quantum computers, an improved understanding i... more In order to realize the full potential of ion trap quantum computers, an improved understanding is required of the motional heating that trapped ions experience. Experimental studies of the temperature-, frequency-, and ion–electrode distance-dependence of the electric field noise responsible for motional heating, as well as the noise before and after ion bombardment cleaning of trap electrodes, suggest that fluctuations of adsorbate dipoles are a likely source of so-called ‘anomalous heating,’ or motional heating of the trapped ions at a rate much higher than the Johnson noise limit. Previous computational studies have investigated how the fluctuation of model adsorbate dipoles affects anomalous heating. However, the way in which specific adsorbates affect the electric field noise has not yet been examined, and an electric dipole model employed in previous studies is only accurate for a small subset of possible adsorbates. Here, we analyze the behavior of both in-plane and out-of-p...

Understanding Li+ transfer at graphite-electrolyte interfaces is key to th... more Understanding Li+ transfer at graphite-electrolyte interfaces is key to the development of next-generation lithium ion batteries. In this work, we investigate the Li+ kinetics at these interfaces and we elucidate key factors that determine the ion transport from first-principles, by coupling ab-initio molecular dynamics simulations with solvation model calculations. We show that surface chemical composition significantly influences the kinetics of ion intercalation from the liquid into the graphite anode. We find that this is partly related to the ion desolvation process, which varies notably for different graphite surfaces. In addition, interfacial polarization is found to play an important role in determining energy barriers for ion transfer. We also discuss the impact of electrode potentials, which is often neglected in conventional first-principles calculations despite being a key factor in device configurations. Our study provides i...

Journal of Applied Physics, 2014

We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing wit... more We investigate point defects in the buffer layers CdS and ZnS that may arise from intermixing with Cu(In,Ga)(S,Se)2 (CIGS) or Cu2ZnSn(S,Se)4 (CZTS) absorber layers in thin-film photovoltaics. Using hybrid functional calculations, we characterize the electrical and optical behavior of Cu, In, Ga, Se, Sn, Zn, Na, and K impurities in the buffer. We find that In and Ga substituted on the cation site act as shallow donors in CdS and tend to enhance the prevailing n-type conductivity at the interface facilitated by Cd incorporation in CIGS, whereas they are deep donors in ZnS and will be less effective dopants. Substitutional In and Ga can favorably form complexes with cation vacancies (A-centers) which may contribute to the “red kink” effect observed in some CIGS-based devices. For CZTS absorbers, we find that Zn and Sn defects substituting on the buffer cation site are electrically inactive in n-type buffers and will not supplement the donor doping at the interface as in CIGS/CdS or ZnS...

The Journal of Physical Chemistry C, 2017

Journal of Applied Physics, 2017

In this paper, the properties of point defects in Cd1−xZnxTe1−ySey (CZTS) radiation detectors are... more In this paper, the properties of point defects in Cd1−xZnxTe1−ySey (CZTS) radiation detectors are characterized using deep-level transient spectroscopy and compared between materials grown using two different methods, the Bridgman method and the traveling heater method. The nature of the traps was analyzed in terms of their capture cross-sections and trap concentrations, as well as their effects on the measured charge-carrier trapping and de-trapping times, and then compared for the two growth techniques. The results revealed that Se addition to CdZnTe can reduce the VCd− concentration. In Travelling Heater Method (THM) and Bridgman Method (BM) grown CZTS detectors, besides a few similarities in the shallow and medium energy traps, there were major differences in the deep traps. It was observed that the excess-Te and lower growth-temperature conditions in THM-grown CZTS led to a complete compensation of VCd− and two additional traps (attributed to Tei− and TeCd++ appearing at around...

2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015

The Cu migration behavior in PVD-CdS/PVD-Cu(In,Ga)Se2 (CIGS) heterojunctions is investigated by h... more The Cu migration behavior in PVD-CdS/PVD-Cu(In,Ga)Se2 (CIGS) heterojunctions is investigated by high resolution electron microscopy and energy dispersive X-ray spectroscopy (EDS) mapping. The incorporation of Cu into CdS forms Cu-rich domains in the CdS across the heterojunction and has no effect on epitaxy of the CdS film, which is commonly observed in the materials studied. In some cases Cd is completely replaced by Cu, resulting in a Cu-S binary compound epitaxially grown on the CIGS and fully coherent with the surrounding CdS, which is most likely cubic Cu2S by lattice spacing measurement from HREM images and EDS elemental quantification. The presence of a binary Cu-S phase as a heterojunction partner material may have significant impact on the resulting device performance although only modest loss of Voc occurs in the devices studied.

Springer Series in Materials Science, 2015

Phase Change Materials should be stable enough in their amorphous phase to achieve a durable data... more Phase Change Materials should be stable enough in their amorphous phase to achieve a durable data retention, however they should also be bad glass formers to be able to recrystallise at high speed. To understand these contradicting properties, we construct models of amorphous Ge–Sb–Te systems using Ab Initio Molecular Dynamics and analyse the structures in relation with the relevant crystalline state. We show that structural patterns that are precursors of the crystalline phase exist in the amorphous state and we identify the signature of the various types of local atomic orders in the X-ray absorption spectra that we compute using Density Functional Theory. We first analyse the mechanical properties of the amorphous phase in the framework of the Maxwell rigidity theory, showing that all efficient Phase Change Materials deviate from the perfect glass and are mechanically stressed-rigid. Additionally, we show that the stability of Phase Change Materials is related to the density of low frequency vibrational modes (Boson peak). We describe how an adequate doping can result in an increased stability of the amorphous phase while keeping intact the phase change ability of the material.

The performance of high resolution semiconductor based radiation detectors at room temperature is... more The performance of high resolution semiconductor based radiation detectors at room temperature is hindered by intrinsic defects and accidental impurities. Experimental efforts to improve the properties of such materials are both time consuming and expensive, since they rely to a large extent on trial and error. In this talk, we show how a fully ab-initio approach allows ranking the most detrimental defects in a crystal in terms of carrier recombination and charge transport. The method was applied to gallium telluride and gallium selenide, both moderate gap layered semiconductors. Based on our results, we can tailor experimental processes to grow these semiconductors with optimal properties. This can be achieved by tuning the growth conditions to avoid the most harmful defects or by compensating them through the introduction of dopants that counteract their detrimental electronic behavior without adding significant scattering to propagating wavepackets in the material.