87 results found
Peng Y, Huq T, Mei J, et al., 2020, Lead-free perovskite-inspired absorbers for indoor photovoltaics, Advanced Energy Materials, Vol: 11, Pages: 1-12, ISSN: 1614-6832
With the exponential rise in the market value and number of devices part of the Internet of Things (IoT), the demand for indoor photovoltaics (IPV) to power autonomous devices is predicted to rapidly increase. Lead‐free perovskite‐inspired materials (PIMs) have recently attracted significant attention in photovoltaics research, due to the similarity of their electronic structure to high‐performance lead‐halide perovskites, but without the same toxicity limitations. However, the capability of PIMs for indoor light harvesting has not yet been considered. Herein, two exemplar PIMs, BiOI and Cs3Sb2ClxI9‐x are examined. It is shown that while their bandgaps are too wide for single‐junction solar cells, they are close to the optimum for indoor light harvesting. As a result, while BiOI and Cs3Sb2ClxI9‐x devices are only circa 1%‐efficient under 1‐sun illumination, their efficiencies increase to 4–5% under indoor illumination. These efficiencies are within the range of reported values for hydrogenated amorphous silicon, i.e., the industry standard for IPV. It is demonstrated that such performance levels are already sufficient for millimeter‐scale PIM devices to power thin‐film‐transistor circuits. Intensity‐dependent and optical loss analyses show that future improvements in efficiency are possible. Furthermore, calculations of the optically limited efficiency of these and other low‐toxicity PIMs reveal their considerable potential for IPV, thus encouraging future efforts for their exploration for powering IoT devices.
Raninga RD, Jagt RA, Béchu S, et al., 2020, Strong performance enhancement in lead-halide perovskite solar cells through rapid, atmospheric deposition of n-type buffer layer oxides, Nano Energy, Vol: 75, Pages: 104946-104946, ISSN: 2211-2855
Jagt RA, Huq TN, Hill SA, et al., 2020, Rapid vapor-phase deposition of high-mobility p-Type buffer layers on perovskite photovoltaics for efficient semi-transparent devices, ACS Energy Letters, Vol: 5, Pages: 2456-2465, ISSN: 2380-8195
Perovskite solar cells (PSCs) with transparent electrodes can be integrated with existing solar panels in tandem configurations to increase the power conversion efficiency. A critical layer in semi-transparent PSCs is the inorganic buffer layer, which protects the PSC against damage when the transparent electrode is sputtered on top. The development of n-i-p structured semi-transparent PSCs has been hampered by the lack of suitable p-type buffer layers. In this work we develop a p-type CuOx buffer layer, which can be grown uniformly over the perovskite device without damaging the perovskite or organic hole transport layers. The CuOx layer has high hole mobility (4.3 ± 2 cm2 V-1 s-1), high transmittance (>95%), and a suitable ionization potential for hole extraction (5.3 ± 0.2 eV). Semi-transparent PSCs with efficiencies up to 16.7% are achieved using the CuOx buffer layer. Our work demonstrates a new approach to integrate n-i-p structured PSCs into tandem configurations, as well as enable the development of other devices that need high quality, protective p-type layers.
Hoye R, Fakharuddin A, Congreve D, et al., 2020, Light emission from perovskite materials, APL Materials, Vol: 8, Pages: 070401-1-070401-3, ISSN: 2166-532X
Napari M, Huq TN, Maity T, et al., 2020, Antiferromagnetism and p‐type conductivity of nonstoichiometric nickel oxide thin films, Infomat, Vol: 2, Pages: 769-774, ISSN: 2567-3165
Plasma‐enhanced atomic layer deposition was used to grow non‐stoichiometric nickel oxide thin films with low impurity content, high crystalline quality, and p‐type conductivity. Despite the non‐stoichiometry, the films retained the antiferromagnetic property of NiO.
Jagt RA, Huq TN, Börsig KM, et al., 2020, Controlling the preferred orientation of layered BiOI solar absorbers, Journal of Materials Chemistry C, Vol: 15 jun 2020, Pages: 10791-10797, ISSN: 2050-7526
Bismuth oxyiodide (BiOI) has gained attention for photovoltaics, photocatalysis and photodetectors owing to its composition of non-toxic elements, tolerance to point defects, and highly-suitable optical properties. But like many other bismuth-based compounds, BiOI is a layered material with anisotropic transport properties, making control over the preferred orientation critical for achieving optimal device performance. In this work, we develop new insights into the growth mechanism of BiOI synthesized by chemical vapor deposition (CVD) and show how the preferred orientation can be controlled. By adjusting the precursor and substrate temperatures to tune whether or not we are in a nucleation- or growth-controlled regime, we reproducibly vary the ratio of the (001) and (110) orientations by over two orders of magnitude. As a result, we achieve highly c-axis oriented films, which leads to less shunting than a/b-axis oriented films, resulting in improved open-circuit voltages from a median value of 0.7 V (a/b-axis oriented) to 0.9 V (c-axis oriented) in BiOI solar cells. More broadly, the described mechanisms can be used to control the preferred orientation in other low-dimensional materials, which will be important for achieving improved performance across a wide variety of devices.
Gan J, Hoye R, Ievskaya Y, et al., 2020, Elucidating the origin of external quantum efficiency losses in cuprous oxide solar cells through defect analysis, Solar Energy Materials and Solar Cells, Vol: 209, Pages: 1-8, ISSN: 0165-1633
Heterojunction Cu2O solar cells are an important class of earth-abundant photovoltaics that can be synthesized by a variety of techniques, including electrochemical deposition (ECD) and thermal oxidation (TO). The latter gives the most efficient solar cells of up to 8.1 %, but is limited by low external quantum efficiencies (EQE) in the long wavelength region. By contrast, ECD Cu2O gives higher short wavelength EQEs of up to 90 %. We elucidate the cause of this difference by characterizing and comparing ECD and TO films using impedance spectroscopy and fitting with a lumped circuit model to determine the trap density, followed by simulations. The data indicates that TO Cu2O has a higher density of interface defects, located approximately 0.5 eV above the valence band maximum (NV),and lower bulk defect density thus explaining the lower short wavelength EQEs and higher long wavelength EQEs. This work shows that a route to further efficiency increases of TO Cu2O is to reduce the density of interface defect states.
Peng Y, Li F, Wang Y, et al., 2020, Enhanced photoconversion efficiency in cesium-antimony-halide perovskite derivatives by tuning crystallographic dimensionality, Applied Materials Today, Vol: 19, Pages: 1-11, ISSN: 2352-9407
Lead-based perovskites have reached prominence in optoelectronic and photovoltaic research, yet their toxicity has prompted the search for alternative lead-free compounds. All-inorganic antimony-/bismuth-halide perovskite derivatives have been identified as a promising class of materials. Despite attractive bulk optoelectronic properties, their optoelectronic device performance has been lagging behind. Here we examine one of their most promising embodiments, the all-inorganic cesium-antimony-halide system. Through solution-based halide mixing, we achieve its structural conversion from a zero-dimensional to a layered phase at processing temperatures <150 °C, i.e., much lower than those relied upon in the prior literature (≥230 °C) of all-inorganic cesium-antimony halides. In order to evaluate the technological significance of this finding, we integrate our layered films into a sandwich-type device structure, and characterize their external quantum efficiency and photovoltaic behavior. We find that the structural conversion leads to a considerable enhancement in the optoelectronic device performance. Additionally, photocurrent-power characterization and Hall effect measurements reveal that this performance enhancement is brought about by an improvement in charge carrier transport, which can be exploited due to the unoriented nature of our low-temperature-processed layered films. Such performance boost and mechanistic insight constitute an important step in realizing the full potential of these (and related) compounds for their application in lead-free optoelectronic and photovoltaic devices, e.g., for top-cell in tandem photovoltaics, indoor photovoltaics, and photodetectors.
Huq T, Lee L, Eyre L, et al., 2020, Electronic structure and optoelectronic properties of bismuth Ooxyiodide robust against percent-level iodine-, oxygen- and bismuth-related surface defects, Advanced Functional Materials, Vol: 30, Pages: 1-11, ISSN: 1616-301X
In the search for nontoxic alternatives to lead‐halide perovskites, bismuth oxyiodide (BiOI) has emerged as a promising contender. BiOI is air‐stable for over three months, demonstrates promising early‐stage photovoltaic performance and, importantly, is predicted from calculations to tolerate vacancy and antisite defects. Here, whether BiOI tolerates point defects is experimentally investigated. BiOI thin films are annealed at a low temperature of 100 °C under vacuum (25 Pa absolute pressure). There is a relative reduction in the surface atomic fraction of iodine by over 40%, reduction in the surface bismuth fraction by over 5%, and an increase in the surface oxygen fraction by over 45%. Unexpectedly, the Bi 4f7/2 core level position, Fermi level position, and valence band density of states of BiOI are not significantly changed. Further, the charge‐carrier lifetime, photoluminescence intensity, and the performance of the vacuum‐annealed BiOI films in solar cells remain unchanged. The results show BiOI to be electronically and optoelectronically robust to percent‐level changes in surface composition. However, from photoinduced current transient spectroscopy measurements, it is found that the as‐grown BiOI films have deep traps located ≈0.3 and 0.6 eV from the band edge. These traps limit the charge‐carrier lifetimes of BiOI, and future improvements in the performance of BiOI photovoltaics will need to focus on identifying their origin. Nevertheless, these deep traps are three to four orders of magnitude less concentrated than the surface point defects induced through vacuum annealing. The charge‐carrier lifetimes of the BiOI films are also orders of magnitude longer than if these surface defects were recombination active. This work therefore shows BiOI to be robust against processing conditions that lead to percent‐level iodine‐, bismuth‐, and oxygen‐related surface defects. This will simplify and reduce the cost of fabricating BiOI‐based electronic devices
Gonzalez Rodriguez R, Costa V, Delport G, et al., 2020, Structural and spectroscopic studies of a nanostructured silicon – perovskite interface, Nanoscale, Vol: 12, Pages: 4498-4505, ISSN: 2040-3364
While extensively investigated in thin film form for energy materials applications, this work investigates the formation of APbBr3 structures (A = CH3NH3+ (MA), Cs+) in silicon and oxidized silicon nanotubes (SiNTs) with varying inner diameter. We carefully control the extent of oxidation of the nanotube host and correlate the relative Si/Si oxide content in a given nanotube host with the photoluminescence quantum efficiency (PLQE) of the perovskite. Complementing these measurements is an evaluation of average PL lifetimes of a given APbBr3 nanostructure, as evaluated by time-resolved confocal photoluminescence measurements. Increasing Si (decreasing oxide) content in the nanotube host results in a sensitive reduction of MAPbBr3 PLQE, with a concomitant decrease in average lifetime (τave). We interpret these observations in terms of decreased defect passivation by a lower concentration of oxide species surrounding the perovskite. In addition, we show that the use of selected nanotube templates leads to more stable perovskite PL in air over time (weeks). Taken in concert, such fundamental observations have implications for interfacial carrier interactions in tandem Si/perovskite photovoltaics.
Li F, Wang Y, Xia K, et al., 2020, Microstructural and photoconversion efficiency enhancement of compact films of lead-free perovskite derivative Rb3Sb2I9, Journal of Materials Chemistry A, Vol: 8, Pages: 4396-4406, ISSN: 2050-7488
While lead-based perovskites have held center stage in photovoltaic and optoelectronic research over the past decade, their toxicity has raised significant concerns, spurring the search for lead-free alternatives with similar potential. While a number of lead-free antimony-/bismuth-based compounds have been proposed, they have typically exhibited limited charge extraction efficiency, which has prompted the widespread adoption of a mesoporous device architecture. With a focus on compact films of Rb3Sb2I9—an emerging lead-free two-dimensional perovskite derivative—this study presents two strategies to enhance their microstructure: one relying on the reduction of the supersaturation level during the annealing step, and the other involving high-temperature annealing in an SbI3 atmosphere. Both strategies lead to a considerable improvement in film morphology and microstructure, with a twofold increase in apparent grain size. Such high-quality compact films deliver a pronounced rise in external quantum efficiency, as well as in short-circuit photocurrent under solar illumination—all this without the aid of a mesoporous architecture for charge extraction. Hall effect and photocurrent-power characterization show that this performance improvement results from an increase in charge carrier mobility and a reduction in the number of recombination centers. The microstructural improvement, photoconversion efficiency boost, and mechanistic insight provide valuable indications on the status and prospects of Rb3Sb2I9 and related derivatives—as relevant to the future exploration of these compounds for lead-free top-cells in tandem photovoltaics, indoor photovoltaics, and other optoelectronic application domains.
Li Y, Hoye RLZ, Gao H, et al., 2020, Over 20% efficiency in methylammonium lead Iodide perovskite solar cells with enhanced stability via “in-situ solidification” of the TiO2 compact layer, ACS Applied Materials & Interfaces, Vol: 12, Pages: 7135-7143, ISSN: 1944-8244
In methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs), the device performance is strongly influenced by the TiO2 elec-tron transport layer (ETL). Typically, the ETL needs to simultaneously be thin and pinhole-free in order to have high transmittance and avoid shunting. In this work, we develop an “in-situ solidification” process following spin coating, in which the titanium-based precursor (ti-tanium (diisopropoxide) bis (2,4-pentaneclionate)) is dried under vacuum to rapidly achieve continuous TiO2 layers. We refer to this as gas-phase quenching. This results in thin (60±10 nm), uniform and pinhole-free TiO2 films. The PSCs based on the gas-phase quenched TiO2 exhibits improved power conversion efficiency, with a median value of 18.23% (champion value of 20.43%), compared to 9.03% and 14.09% for the untreated devices. Gas-phase quenching is further shown to be effective in enabling efficient charge transfer at the MAPbI3/TiO2 heterointerface. Furthermore, the stability of the gas-phase quenched devices is enhanced in ambient air as well as under 1-sun illumination. In addition, we achieve 12.1% efficiency in upscaled devices (1.1 cm2 active area).
Shin M, Nam S-W, Sadhanala A, et al., 2019, Understanding the Origin of Ultrasharp Sub-bandgap Luminescence from Zero-Dimensional Inorganic Perovskite Cs4PbBr6, ACS Applied Energy Materials, ISSN: 2574-0962
Stranks SD, Hoye RLZ, Di D, et al., 2019, The physics of light emission in halide perovskite devices, Advanced Materials, Vol: 31, Pages: 1-11, ISSN: 0935-9648
Light emission is a critical property that must be maximized and controlled to reach the performance limits in optoelectronic devices such as photovoltaic solar cells and light‐emitting diodes. Halide perovskites are an exciting family of materials for these applications owing to uniquely promising attributes that favor strong luminescence in device structures. Herein, the current understanding of the physics of light emission in state‐of‐the‐art metal‐halide perovskite devices is presented. Photon generation and management, and how these can be further exploited in device structures, are discussed. Key processes involved in photoluminescence and electroluminescence in devices as well as recent efforts to reduce nonradiative losses in neat films and interfaces are discussed. Finally, pathways toward reaching device efficiency limits and how the unique properties of perovskites provide a tremendous opportunity to significantly disrupt both the power generation and lighting industries are outlined.
Ahmad S, Sadhanala A, Hoye RLZ, et al., 2019, Triple-cation-based perovskite photocathodes with AZO protective layer for hydrogen production applications, ACS Applied Materials & Interfaces, Vol: 11, Pages: 23198-23206, ISSN: 1944-8244
Metal halide perovskites are actively pursued as photoelectrodes to drive solar fuel synthesis. However, currently, these photocathodes suffer from limited stability in water, which hampers their practical application. Here, we report a high-performance solution-processable photocathode composed of cesium formamidinium methylammonium triple-cation lead halide perovskite protected by an Al-doped ZnO (AZO) layer combined with a Field’s metal encapsulation. Careful selection of charge transport layers resulted in an improvement in photocurrent, fill factor, device stability and reproducibility. The dead pixels count reduced from 25 to 6% for the devices with an AZO layer, and in photocathodes with an AZO layer the photocurrent density increased by almost 20% to 14.3 mA cm–2. In addition, we observed a 5-fold increase in the device lifetime for photocathodes with AZO, which reached up to 18 h before complete failure. Finally, the photocathodes are fabricated using low-cost and scalable methods, which have promise to become compatible with standard solution-based processes.
Gan J, He J, Hoye RLZ, et al., 2019, α-CsPbI3 Colloidal Quantum Dots: Synthesis, Photodynamics, and Photovoltaic Applications, ACS Energy Letters, Vol: 4, Pages: 1308-1320, ISSN: 2380-8195
Owing to their defect tolerance and phase stability, α-CsPbI3 colloidal quantum dots (CQDs) with high mobility and 80–95% photoluminescence quantum yield (PLQY) are promising candidates for next-generation photovoltaics (PVs). Recently, α-CsPbI3 CQD PVs have begun to show promising power conversion efficiencies of 13.4%, with the open-circuit voltage approaching the Shockley–Queisser limit. These devices are stable in ambient conditions for several months. However, the short-circuit current density (JSC) of ∼12 mA/cm2 is low, and the limiting mechanisms are unclear. In this work, we review the strategies for improving the JSC and the effect of interfaces and mobility of the charge transport layers on carrier extraction. We also evaluate strategies to enhance the stability of CsPbI3 CQDs under illumination, as well as methods to elucidate the recombination losses in the CQD PVs and methods to reduce these losses. This work provides routes to achieve efficient and stable α-CsPbI3 CQD PVs.
Hoye R, MacManus-Driscoll J, 2019, Atmospheric Pressure Spatial Atomic Layer Deposited Metal Oxides for Thin Film Solar Cells, Advanced Micro- and Nanomaterials for Photovoltaics, Editors: Fix, Ginley, Publisher: Elsevier, Pages: 245-277
Atmospheric pressure spatial atomic layer deposition has recently gained traction as an attractive method for rapidly growing oxide thin films. In this chapter, we compare the reactors that have been developed in laboratories and in industry. We review the n-type and p-type materials that have been grown and discuss how these materials, with widely tunable properties, have been used to improve the performance of solar cells. In addition, we explore the use of AP-SALD in complex structures and discuss future opportunities of AP-SALD for solar cells.
Hoye RLZ, Lai M-L, Anaya M, et al., 2019, Identifying and reducing interfacial losses to enhance color-pure electroluminescence in blue-emitting perovskite nanoplatelet light-emitting diodes, ACS Energy Letters, Vol: 4, Pages: 1181-1188, ISSN: 2380-8195
Perovskite nanoplatelets (NPls) hold promise for light-emitting applications, having achieved photoluminescence quantum efficiencies approaching unity in the blue wavelength range, where other metal-halide perovskites have typically been ineffective. However, the external quantum efficiencies (EQEs) of blue-emitting NPl light-emitting diodes (LEDs) have reached only 0.12%. In this work, we show that NPl LEDs are primarily limited by a poor electronic interface between the emitter and hole injector. We show that the NPls have remarkably deep ionization potentials (≥6.5 eV), leading to large barriers for hole injection, as well as substantial nonradiative decay at the NPl/hole-injector interface. We find that an effective way to reduce these nonradiative losses is by using poly(triarylamine) interlayers, which lead to an increase in the EQE of the blue (464 nm emission wavelength) and sky-blue (489 nm emission wavelength) LEDs to 0.3% and 0.55%, respectively. Our work also identifies the key challenges for further efficiency increases.
Zhao B, Lee LC, Yang L, et al., 2018, In situ atmospheric deposition of ultrasmooth Nickel Oxide for efficient perovskite solar cells, ACS Applied Materials & Interfaces, Vol: 10, Pages: 41849-41854, ISSN: 1944-8244
Organic–inorganic perovskite solar cells have attracted significant attention due to their remarkable performance. The use of alternative metal-oxide charge-transport layers is a strategy to improving device reliability for large-scale fabrication and long-term applications. Here, we report solution-processed perovskite solar cells employing nickel oxide hole-extraction layers produced in situ using an atmospheric pressure spatial atomic-layer deposition system, which is compatible with high-throughput processing of electronic devices from solution. Our sub-nanometer smooth (average roughness of ≤0.6 nm) oxide films enable the efficient collection of holes and the formation of perovskite absorbers with high electronic quality. Initial solar-cell experiments show a power-conversion efficiency of 17.1%, near-unity ideality factors, and a fill factor of >80% with negligible hysteresis. Transient measurements reveal that a key contributor to this performance is the reduced luminescence quenching trap density in the perovskite/nickel oxide structure.
Li W, Jiang K, Li Z, et al., 2018, Origin of improved photoelectrochemical water splitting in mixed perovskite oxides, Advanced Energy Materials, Vol: 8, Pages: 1-7, ISSN: 1614-6832
Owing to the versatility in their chemical and physical properties, transition metal perovskite oxides have emerged as a new category of highly efficient photocatalysts for photoelectrochemical (PEC) water splitting. Here, to understand the underlying mechanism for the enhanced PEC water splitting in mixed perovskites, ideal epitaxial thin films of the BiFeO3–SrTiO3 system are explored. The electronic structure and carrier dynamics are determined from both experiment and density‐functional theory calculations. The intrinsic phenomena are measured in this ideal system, contrasting to commonly studied polycrystalline solid solutions where extrinsic structural features obscure the intrinsic phenomena. It is determined that when SrTiO3 is added to BiFeO3 the conduction band minimum position is raised and an exponential tail of trap states from hybridized Ti 3d and Fe 3d orbitals emerges near the conduction band edge. The presence of these trap states strongly suppresses the fast electron–hole recombination and improves the photocurrent density in the visible‐light region, up to 16× at 0 VRHE compared to the pure end member compositions. This work provides a new design approach for optimizing the PEC performance in mixed perovksite oxides.
Cossuet T, Resende J, Rapenne L, et al., 2018, ZnO/CuCrO2 Core-Shell Nanowire Heterostructures for Self-Powered UV Photodetectors with Fast Response, Advanced Functional Materials, Vol: 28, Pages: 1803142-1803142, ISSN: 1616-301X
Andrei V, Hoye RLZ, Crespo-Quesada M, et al., 2018, Scalable triple cation mixed halide perovskite-BiVO4 tandems for bias-free water splitting, Advanced Energy Materials, Vol: 8, Pages: 1-14, ISSN: 1614-6832
Strong interest exists in the development of organic–inorganic lead halide perovskite photovoltaics and of photoelectrochemical (PEC) tandem absorber systems for solar fuel production. However, their scalability and durability have long been limiting factors. In this work, it is revealed how both fields can be seamlessly merged together, to obtain scalable, bias‐free solar water splitting tandem devices. For this purpose, state‐of‐the‐art cesium formamidinium methylammonium (CsFAMA) triple cation mixed halide perovskite photovoltaic cells with a nickel oxide (NiOx) hole transport layer are employed to produce Field's metal‐epoxy encapsulated photocathodes. Their stability (up to 7 h), photocurrent density (–12.1 ± 0.3 mA cm−2 at 0 V versus reversible hydrogen electrode, RHE), and reproducibility enable a matching combination with robust BiVO4 photoanodes, resulting in 0.25 cm2 PEC tandems with an excellent stability of up to 20 h and a bias‐free solar‐to‐hydrogen efficiency of 0.35 ± 0.14%. The high reliability of the fabrication procedures allows scaling of the devices up to 10 cm2, with a slight decrease in bias‐free photocurrent density from 0.39 ± 0.15 to 0.23 ± 0.10 mA cm−2 due to an increasing series resistance. To characterize these devices, a versatile 3D‐printed PEC cell is also developed.
Hoye RLZ, Eyre L, Wei F, et al., 2018, Fundamental carrier lifetime exceeding 1 µs in Cs2AgBiBr6 double perovskite, Advanced Materials Interfaces, Vol: 5, Pages: 1-8, ISSN: 2196-7350
There is current interest in finding nontoxic alternatives to lead‐halide perovskites for optoelectronic applications. Silver–bismuth double perovskites have recently gained attention, but evaluating their carrier lifetime and recombination mechanisms from photoluminescence measurements is challenging due to their indirect bandgap. In this work, transient absorption spectroscopy is used to directly track the photocarrier population in Cs2AgBiBr6 by measuring the ground state bleach dynamics. A small initial drop is resolved in the ground state bleach on a picosecond timescale, after which the remaining photocarriers decay monoexponentially with a lifetime of 1.4 µs. The majority of the early‐time decay is attributed to hot‐carrier thermalization from the direct transition to the indirect bandgap, and the 1.4 µs lifetime represents the recombination of most photocarriers. From this lifetime, a steady‐state excess carrier density of 2.2 × 1016 cm−3 under 1 sun is calculated, which is an order of magnitude larger than that for methylammonium lead iodide, suggesting that charge transport and extraction can be efficient in Cs2AgBiBr6 solar cells.
Bohn BJ, Tong Y, Gramlich M, et al., 2018, Boosting tunable blue luminescence of halide perovskite nanoplatelets through postsynthetic surface trap repair, Nano Letters, Vol: 18, Pages: 5231-5238, ISSN: 1530-6984
The easily tunable emission of halide perovskite nanocrystals throughout the visible spectrum makes them an extremely promising material for light-emitting applications. Whereas high quantum yields and long-term colloidal stability have already been achieved for nanocrystals emitting in the red and green spectral range, the blue region currently lags behind with low quantum yields, broad emission profiles, and insufficient colloidal stability. In this work, we present a facile synthetic approach for obtaining two-dimensional CsPbBr3 nanoplatelets with monolayer-precise control over their thickness, resulting in sharp photoluminescence and electroluminescence peaks with a tunable emission wavelength between 432 and 497 nm due to quantum confinement. Subsequent addition of a PbBr2-ligand solution repairs surface defects likely stemming from bromide and lead vacancies in a subensemble of weakly emissive nanoplatelets. The overall photoluminescence quantum yield of the blue-emissive colloidal dispersions is consequently enhanced up to a value of 73 ± 2%. Transient optical spectroscopy measurements focusing on the excitonic resonances further confirm the proposed repair process. Additionally, the high stability of these nanoplatelets in films and to prolonged ultraviolet light exposure is shown.
Hoye RLZ, Bush KA, Oviedo F, et al., 2018, Developing a Robust Recombination Contact to Realize Monolithic Perovskite Tandems With Industrially Common p-Type Silicon Solar Cells, IEEE Journal of Photovoltaics, Vol: 8, Pages: 1023-1028, ISSN: 2156-3381
Lee LC, Huq TN, MacManus-Driscoll JL, et al., 2018, Research Update: Bismuth-based perovskite-inspired photovoltaic materials, APL Materials, Vol: 6, Pages: 084502-1-084502-16
Bismuth-based compounds have recently gained interest as solar absorbers with the potential to have low toxicity, be efficient in devices, and be processable using facile methods. We review recent theoretical and experimental investigations into bismuth-based compounds, which shape our understanding of their photovoltaic potential, with particular focus on their defect-tolerance. We also review the processing methods that have been used to control the structural and optoelectronic properties of single crystals and thin films. Additionally, we discuss the key factors limiting their device performance, as well as the future steps needed to ultimately realize these new materials for commercial applications.
Nagane S, Ghosh D, Hoye RLZ, et al., 2018, Lead-free perovskite semiconductors based on germanium–tin solid solutions: structural and optoelectronic properties, The Journal of Physical Chemistry C, Vol: 122, Pages: 5940-5947, ISSN: 1932-7447
Solar cells and optoelectronics based on lead halide perovskites are generating considerable interest but face challenges with the use of toxic lead. In this study, we fabricate and characterize lead-free perovskites based on germanium and tin solid solutions, CH3NH3Sn(1–x)GexI3 (0 ≤ x ≤ 1). We show that these perovskite compounds possess band gaps from 1.3 to 2.0 eV, which are suitable for a range of optoelectronic applications, from single junction devices and top cells for tandems to light-emitting layers. Their thermodynamic stability and electronic properties are calculated for all compositions and agree well with our experimental measurements. Our findings demonstrate an attractive family of lead-free perovskite semiconductors with a favorable band-gap range for efficient single-junction solar cells.
Zhang JY, Li WW, Hoye RLZ, et al., 2018, Electronic and transport properties of Li-doped NiO epitaxial thin films, Journal of Materials Chemistry C, Vol: 6, Pages: 2275-2282, ISSN: 2050-7526
NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. Understanding and improving its optical and transport properties have been of considerable interest. In this work, we have investigated the effect of Li doping on the electronic, optical and transport properties of NiO epitaxial thin films grown by pulsed laser deposition. We show that Li doping significantly increases the p-type conductivity of NiO, but all the films have relatively low room-temperature mobilities (<0.05 cm2 V−1 s−1). The conduction mechanism is better described by small-polaron hoping model in the temperature range of 200 K < T < 330 K, and variable range hopping at T < 200 K. A combination of X-ray photoemission and O K-edge X-ray absorption spectroscopic investigations reveal that the Fermi level gradually shifts toward the valence band maximum (VBM) and a new hole state develops with Li doping. Both the VBM and hole states are composed of primarily Zhang-Rice bound states, which accounts for the small polaron character (low mobility) of hole conduction. Our work provides guidelines for the search for p-type oxide materials and device optimization.
Hoye RLZ, Lee LC, Kurchin RC, et al., 2017, Strongly enhanced photovoltaic performance and defect physics of air-stable bismuth oxyiodide (BiOI), Advanced Materials, Vol: 29, ISSN: 0935-9648
Bismuth‐based compounds have recently gained increasing attention as potentially nontoxic and defect‐tolerant solar absorbers. However, many of the new materials recently investigated show limited photovoltaic performance. Herein, one such compound is explored in detail through theory and experiment: bismuth oxyiodide (BiOI). BiOI thin films are grown by chemical vapor transport and found to maintain the same tetragonal phase in ambient air for at least 197 d. The computations suggest BiOI to be tolerant to antisite and vacancy defects. All‐inorganic solar cells (ITO|NiOx|BiOI|ZnO|Al) with negligible hysteresis and up to 80% external quantum efficiency under select monochromatic excitation are demonstrated. The short‐circuit current densities and power conversion efficiencies under AM 1.5G illumination are nearly double those of previously reported BiOI solar cells, as well as other bismuth halide and chalcohalide photovoltaics recently explored by many groups. Through a detailed loss analysis using optical characterization, photoemission spectroscopy, and device modeling, direction for future improvements in efficiency is provided. This work demonstrates that BiOI, previously considered to be a poor photocatalyst, is promising for photovoltaics.
Bai F, Zhang Y, Duan Z, et al., 2017, Broadband antireflection property of silicon nanocone arrays with porous sidewalls fabricated by Ag-catalyzed etching, AIP Advances, Vol: 7, ISSN: 2158-3226
Siliconnanocone (SiNC) arrays with porous sidewallswere successfully fabricated through a simple, low-cost Ag-catalyzed etching method. By electron spin resonance technique and TEM analysis, it has been verified that the formation of porous SiNC arrays is due to the gradual dissolution of the pristine Ag nanoislands as they sank into the Si and the lateral etching of the regenerated Ag nanoparticles to the SiNC sidewalls. Theoretical calculation results suggest that the reflectance of the porous SiNC arrays is much lower than that of the smooth SiNC arrays over wide wavelengths ranging from 300nm to 1700nm. The long-wavelength reflectance can be further suppressed by increasing surface porosity of the SiNCs and their length. Experimental test results show the lowest average reflectance of 1.7% in the wavelength range of 300-1000nm while approximately 30% in the wavelength ranges of 1200-1700nm, which is generally consistent with the theoretical results. This shows that the porous SiNC arrays had excellent broadband antireflection properties, making them attractive for a wide range of potential applications in Si-based optoelectronic devices.
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