Publications
87 results found
Polizzotti A, Faghaninia A, Poindexter JR, et al., 2017, Improving the carrier lifetime of tin sulfide via prediction and mitigation of harmful point defects, The Journal of Physical Chemistry Letters, Vol: 8, Pages: 3661-3667, ISSN: 1948-7185
Tin monosulfide (SnS) is an emerging thin-film absorber material for photovoltaics. An outstanding challenge is to improve carrier lifetimes to >1 ns, which should enable >10% device efficiencies. However, reported results to date have only demonstrated lifetimes at or below 100 ps. In this study, we employ defect modeling to identify the sulfur vacancy and defects from Fe, Co, and Mo as most recombination-active. We attempt to minimize these defects in crystalline samples through high-purity, sulfur-rich growth and experimentally improve lifetimes to >3 ns, thus achieving our 1 ns goal. This framework may prove effective for unlocking the lifetime potential in other emerging thin-film materials by rapidly identifying and mitigating lifetime-limiting point defects.
Poindexter JR, Hoye RLZ, Nienhaus L, et al., 2017, High Tolerance to Iron Contamination in Lead Halide Perovskite Solar Cells, ACS Nano, Vol: 11, Pages: 7101-7109, ISSN: 1936-0851
The relationship between charge-carrier lifetime and the tolerance of lead halide perovskite (LHP) solar cells to intrinsic point defects has drawn much attention by helping to explain rapid improvements in device efficiencies. However, little is known about how charge-carrier lifetime and solar cell performance in LHPs are affected by extrinsic defects (i.e., impurities), including those that are common in manufacturing environments and known to introduce deep levels in other semiconductors. Here, we evaluate the tolerance of LHP solar cells to iron introduced via intentional contamination of the feedstock and examine the root causes of the resulting efficiency losses. We find that comparable efficiency losses occur in LHPs at feedstock iron concentrations approximately 100 times higher than those in p-type silicon devices. Photoluminescence measurements correlate iron concentration with nonradiative recombination, which we attribute to the presence of deep-level iron interstitials, as calculated from first-principles, as well as iron-rich particles detected by synchrotron-based X-ray fluorescence microscopy. At moderate contamination levels, we witness prominent recovery of device efficiencies to near-baseline values after biasing at 1.4 V for 60 s in the dark. We theorize that this temporary effect arises from improved charge-carrier collection enhanced by electric fields strengthened from ion migration toward interfaces. Our results demonstrate that extrinsic defect tolerance contributes to high efficiencies in LHP solar cells, which inspires further investigation into potential large-scale manufacturing cost savings as well as the degree of overlap between intrinsic and extrinsic defect tolerance in LHPs and “perovskite-inspired” lead-free stable alternatives.
Brandt RE, Poindexter JR, Gorai P, et al., 2017, Searching for “Defect-Tolerant” Photovoltaic Materials: Combined Theoretical and Experimental Screening, Chemistry of Materials, Vol: 29, Pages: 4667-4674, ISSN: 0897-4756
Recently, we and others have proposed screening criteria for “defect-tolerant” photovoltaic (PV) absorbers, identifying several classes of semiconducting compounds with electronic structures similar to those of hybrid lead–halide perovskites. In this work, we reflect on the accuracy and prospects of these new design criteria through a combined experimental and theoretical approach. We construct a model to extract photoluminescence lifetimes of six of these candidate PV absorbers, including four (InI, SbSI, SbSeI, and BiOI) for which time-resolved photoluminescence has not been previously reported. The lifetimes of all six candidate materials exceed 1 ns, a threshold for promising early stage PV device performance. However, there are variations between these materials, and none achieve lifetimes as high as those of the hybrid lead–halide perovskites, suggesting that the heuristics for defect-tolerant semiconductors are incomplete. We explore this through first-principles point defect calculations and Shockley–Read–Hall recombination models to describe the variation between the measured materials. In light of these insights, we discuss the evolution of screening criteria for defect tolerance and high-performance PV materials.
Bush KA, Palmstrom AF, Yu ZJ, et al., 2017, 23.6%-efficient monolithic perovskite/silicon tandem solar cells with improved stability, Nature Energy, Vol: 2, Pages: 1-7, ISSN: 2058-7546
As the record single-junction efficiencies of perovskite solar cells now rival those of copper indium gallium selenide, cadmium telluride and multicrystalline silicon, they are becoming increasingly attractive for use in tandem solar cells due to their wide, tunable bandgap and solution processability. Previously, perovskite/silicon tandems were limited by significant parasitic absorption and poor environmental stability. Here, we improve the efficiency of monolithic, two-terminal, 1-cm2 perovskite/silicon tandems to 23.6% by combining an infrared-tuned silicon heterojunction bottom cell with the recently developed caesium formamidinium lead halide perovskite. This more-stable perovskite tolerates deposition of a tin oxide buffer layer via atomic layer deposition that prevents shunts, has negligible parasitic absorption, and allows for the sputter deposition of a transparent top electrode. Furthermore, the window layer doubles as a diffusion barrier, increasing the thermal and environmental stability to enable perovskite devices that withstand a 1,000-hour damp heat test at 85 ∘C and 85% relative humidity.
Hoye RLZ, Schulz P, Schelhas LT, et al., 2017, Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations, CHEMISTRY OF MATERIALS, Vol: 29, Pages: 1964-1988, ISSN: 0897-4756
Recently, there has been an explosive growth in research based on hybrid lead–halide perovskites for photovoltaics owing to rapid improvements in efficiency. The advent of these materials for solar applications has led to widespread interest in understanding the key enabling properties of these materials. This has resulted in renewed interest in related compounds and a search for materials that may replicate the defect-tolerant properties and long lifetimes of the hybrid lead-halide perovskites. Given the rapid pace of development of the field, the rises in efficiencies of these systems have outpaced the more basic understanding of these materials. Measuring or calculating the basic properties, such as crystal/electronic structure and composition, can be challenging because some of these materials have anisotropic structures, and/or are composed of both heavy metal cations and volatile, mobile, light elements. Some consequences are beam damage during characterization, composition change under vacuum, or compound effects, such as the alteration of the electronic structure through the influence of the substrate. These effects make it challenging to understand the basic properties integral to optoelectronic operation. Compounding these difficulties is the rapid pace with which the field progresses. This has created an ongoing need to continually evaluate best practices with respect to characterization and calculations, as well as to identify inconsistencies in reported values to determine if those inconsistencies are rooted in characterization methodology or materials synthesis. This article describes the difficulties in characterizing hybrid lead–halide perovskites and new materials and how these challenges may be overcome. The topic was discussed at a seminar at the 2015 Materials Research Society Fall Meeting & Exhibit. This article highlights the lessons learned from the seminar and the insights of some of the attendees, with reference to both recen
Musselman KP, Muñoz-Rojas D, Hoye RLZ, et al., 2017, Rapid open-air deposition of uniform, nanoscale, functional coatings on nanorod arrays, Nanoscale Horizons, Vol: 2, Pages: 110-117, ISSN: 2055-6756
<p>A rapid, open-air technique for the scalable deposition of coatings uniformly conformal to high-aspect-ratio nanorod arrays is demonstrated.</p>
Brandt R, Kurchin R, Buonassisi T, et al., 2016, OPTOELECTRONIC DEVICES FABRICATED WITH DEFECT TOLERANT SEMICONDUCTORS, 2016-0293858
Conventional screening methods for use of semiconductor materials in optoelectronic devices typically emphasize optical properties and scalability concerns. Optical bandgap energy, absorption coefficient, elemental abundance, toxicity, stability, and manufacturing cost of a material represent key criteria for candidate semiconductor materials. However, many materials meet these criteria but fail to achieve industrially relevant conversion efficiencies (above 10-15%) required for high-performance PV materials.Consideration of additional properties that enable bulk transport in the presence of defects can help identify high-performance semiconductor materials with enhanced stability and reduced toxicity. The new design criteria incorporates defect-tolerance in the minority carrier lifetimes of semiconductors and presents a new screening path for candidate materials applicable to optoelectronic devices.
Ievskaya Y, Hoye RLZ, Sadhanala A, et al., 2016, Improved Heterojunction Quality in Cu<sub>2</sub>O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited <br />Zn<sub>1-x</sub>Mg<sub>x</sub>O, Journal of Visualized Experiments
Khare N, Ansari MZ, Hoye RLZ, et al., 2016, Elucidation of barrier homogeneity in ZnO/P3HT:PCBM junctions through temperature dependentI–Vcharacteristics, Journal of Physics D: Applied Physics, Vol: 49, Pages: 275302-275302, ISSN: 0022-3727
Hoye RLZ, Brandt RE, Osherov A, et al., 2016, Methylammonium Bismuth Iodide as a Lead‐Free, Stable Hybrid Organic–Inorganic Solar Absorber, Chemistry – A European Journal, Vol: 22, Pages: 2605-2610, ISSN: 0947-6539
Ren X, Sangle A, Zhang S, et al., 2016, Photoelectrochemical water splitting strongly enhanced in fast-grown ZnO nanotree and nanocluster structures, Journal of Materials Chemistry A, Vol: 4, Pages: 10203-10211, ISSN: 2050-7488
<p>We demonstrated a versatile route to fast-fabricate hierarchical ZnO nanostructures which give rise to high photocurrents.</p>
Brandt RE, Kurchin RC, Hoye RLZ, et al., 2015, Investigation of Bismuth Triiodide (BiI<sub>3</sub>) for Photovoltaic Applications, The Journal of Physical Chemistry Letters, Vol: 6, Pages: 4297-4302, ISSN: 1948-7185
Sadhanala A, Ahmad S, Zhao B, et al., 2015, Blue-Green Color Tunable Solution Processable Organolead Chloride-Bromide Mixed Halide Perovskites for Optoelectronic Applications., Nano Lett, Vol: 15, Pages: 6095-6101
Solution-processed organo-lead halide perovskites are produced with sharp, color-pure electroluminescence that can be tuned from blue to green region of visible spectrum (425-570 nm). This was accomplished by controlling the halide composition of CH3NH3Pb(BrxCl1-x)3 [0 ≤ x ≤ 1] perovskites. The bandgap and lattice parameters change monotonically with composition. The films possess remarkably sharp band edges and a clean bandgap, with a single optically active phase. These chloride-bromide perovskites can potentially be used in optoelectronic devices like solar cells and light emitting diodes (LEDs). Here we demonstrate high color-purity, tunable LEDs with narrow emission full width at half maxima (FWHM) and low turn on voltages using thin-films of these perovskite materials, including a blue CH3NH3PbCl3 perovskite LED with a narrow emission FWHM of 5 nm.
Hoye RLZ, Muñoz-Rojas D, Musselman KP, et al., 2015, Synthesis and Modeling of Uniform Complex Metal Oxides by Close-Proximity Atmospheric Pressure Chemical Vapor Deposition, ACS Applied Materials & Interfaces, Vol: 7, Pages: 10684-10694, ISSN: 1944-8244
Hoye R, 2015, Tuning metal oxides for solar cells and light emitting diodes
This thesis investigates techniques for improving the performance of solarcells and organic light emitting diodes (organic LEDs). In Part I of thisthesis, an examination of the literature shows that it is essential to control the properties of the metal oxides used in these devices in a scalable man-ner. Doping is highlighted as a cost-effective approach, and magnesium incorporation an effective means of tuning the conduction band position ofZnO. Spatial atmospheric atomic layer deposition (SAALD) is introducedas a scalable technique for synthesising metal oxides rapidly in open-air.In Part II of this thesis, a systematic method was first developed to optimise the deposition of zinc magnesium oxide (Zn1−xMgxO) by SAALD. This method involves modelling the SAALD system, followed by experimental fine-tuning. Using the optimised conditions, up to 81 at.% Mg was incorporated into ZnO by SAALD, enabling the bandgap to be tuned from 3.3 eV (no Mg) to 5.5 eV (81 at.% Mg). Next, SAALD Zn1−xMgxO was employed in PbSe colloidal quantum dot solar cells (CQDSCs) to identify the metal oxide band-tail as an open-circuit voltage loss mechanism. Reducing this loss mechanism enabled the open-circuit voltage to be increased from 408 mV to 608 mV, the highest for ZnO-PbSe CQDSCs, as well as increasing device efficiencies. The Schottky barrier contact between Zn1−xMgxO and an indium tin oxide (ITO) transparent top contact was then examined in Cu2O-Zn1−xMgxO heterojunction thin film solar cells. It was found that charge can be transported through the Schottky junction without rectification due to hopping via the metal oxide band-tail, and spatially removing the Schottky barrier from the heterojunction is needed to obtain high efficiencies. This shows that ohmic charge-extraction interfaces are not essential to obtain high performances. Finally, SAALD Zn1−xMgxO was used to reduce the operating voltage of polymer LEDs (based on F8BT and aryl-F8) by more than 10
Hoye RLZ, Muñoz-Rojas D, Nelson SF, et al., 2015, Research Update: Atmospheric pressure spatial atomic layer deposition of ZnO thin films: Reactors, doping, and devices, APL Materials, Vol: 3, Pages: 040701-040701
Ievskaya Y, Hoye RLZ, Sadhanala A, et al., 2015, Fabrication of ZnO/Cu2O heterojunctions in atmospheric conditions: Improved interface quality and solar cell performance, Solar Energy Materials and Solar Cells, Vol: 135, Pages: 43-48, ISSN: 0927-0248
Hoye RLZ, Brandt RE, Ievskaya Y, et al., 2015, Perspective: Maintaining surface-phase purity is key to efficient open air fabricated cuprous oxide solar cells, APL Materials, Vol: 3, Pages: 020901-020901
Hoye RLZ, Chua MR, Musselman KP, et al., 2015, Enhanced Performance in Fluorene‐Free Organometal Halide Perovskite Light‐Emitting Diodes using Tunable, Low Electron Affinity Oxide Electron Injectors, Advanced Materials, Vol: 27, Pages: 1414-1419, ISSN: 0935-9648
Hoye RLZ, Musselman KP, Chua MR, et al., 2015, Bright and efficient blue polymer light emitting diodes with reduced operating voltages processed entirely at low-temperature, Journal of Materials Chemistry C, Vol: 3, Pages: 9327-9336, ISSN: 2050-7526
<p>Efficient and bright blue polyfluorene LEDs, processed entirely below 150 °C, are obtained using an atmospherically synthesized, tunable oxide electron-injector.</p>
Hoye RLZ, Heffernan S, Ievskaya Y, et al., 2014, Engineering Schottky Contacts in Open-Air Fabricated Heterojunction Solar Cells to Enable High Performance and Ohmic Charge Transport, ACS Applied Materials & Interfaces, Vol: 6, Pages: 22192-22198, ISSN: 1944-8244
Hoye RLZ, Ehrler B, Böhm ML, et al., 2014, Improved Open‐ Circuit Voltage in ZnO–PbSe Quantum Dot Solar Cells by Understanding and Reducing Losses Arising from the ZnO Conduction Band Tail, Advanced Energy Materials, Vol: 4, Pages: 1301544-1301544, ISSN: 1614-6832
Musselman KP, AlbertSeifried S, Hoye RLZ, et al., 2014, Improved Exciton Dissociation at Semiconducting Polymer:ZnO Donor:Acceptor Interfaces via Nitrogen Doping of ZnO, Advanced Functional Materials, Vol: 24, Pages: 3562-3570, ISSN: 1616-301X
Hoye RLZ, Musselman KP, MacManus-Driscoll JL, 2013, Research Update: Doping ZnO and TiO<sub>2</sub> for solar cells, APL Materials, Vol: 1, Pages: 060701-060701
Iza DC, Muñoz-Rojas D, Musselman KP, et al., 2013, Nanostructured conformal hybrid solar cells: a promising architecture towards complete charge collection and light absorption, Nanoscale Research Letters, Vol: 8
<jats:title>Abstract</jats:title> <jats:p>We introduce hybrid solar cells with an architecture consisting of an electrodeposited ZnO nanorod array (NRA) coated with a conformal thin layer (<50 nm) of organic polymer-fullerene blend and a quasi-conformal Ag top contact (Thin/NR). We have compared the performance of Thin/NR cells to conventional hybrid cells in which the same NRAs are completely filled with organic blend (Thick/NR). The Thin/NR design absorbs at least as much light as Thick/NR cells, while charge extraction is significantly enhanced due to the proximity of the electrodes, resulting in a higher current density per unit volume of blend and improved power conversion efficiency. The NRAs need not be periodic or aligned and hence can be made very simply.</jats:p>
Hoye RLZ, Muñoz-Rojas D, Iza DC, et al., 2013, High performance inverted bulk heterojunction solar cells by incorporation of dense, thin ZnO layers made using atmospheric atomic layer deposition, Solar Energy Materials and Solar Cells, Vol: 116, Pages: 197-202, ISSN: 0927-0248
Hoye R, Gao W, 2012, Oxidation Behaviour of Ni-Cr-Y2O3 Composite Coatings Synthesised by Sol Enhanced Pulse Electroplating, Journal of Materials Science Research, Vol: 1, ISSN: 1927-0585
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