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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Co-deposition of hole-selective contact and absorber for improving the processability of perovskite solar cells

Simplifying the manufacturing processes of renewable energy technologies is crucial to lowering the barriers to commercialization. In this context, to improve the manufacturability of perovskite solar cells (PSCs), here we have developed a one-step solution-coating procedure in which the hole-selective contact and perovskite light absorber spontaneously form, resulting in efficient inverted PSCs. We observed that phosphonic or carboxylic acids, incorporated into perovskite precursor solutions, self-assemble on the indium tin oxide substrate during perovskite film processing. They form a robust self-assembled monolayer as an excellent hole-selective contact while the perovskite crystallizes. Our approach solves wettability issues and simplifies device fabrication, advancing the manufacturability of PSCs. Our PSC devices with positive-intrinsic-negative (p-i-n) geometry show a power conversion efficiency of 24.5% and retain >90% of their initial efficiency after 1,200 h of operating at the maximum power point under continuous illumination. The approach shows good generality as it is compatible with different self-assembled monolayer molecular systems, perovskites, solvents and processing methods.

14 SOLAR ENERGY↗
DOE OSTI2024

Multifunctional entinostat enhances the mechanical robustness and efficiency of flexible perovskite solar cells and minimodules

Flexible perovskite solar cells (F-PSCs), prized for their nature of soft and high power-weight compatibility, have attracted intensive attention. However, inferior buried perovskite-substrate interfaces due to low interfacial adhesion between perovskites and substrates and large deformation of flexible substrates have greatly limited the performance of F-PSCs. Here, we add organic molecule Entinostat (ET) into hole extraction material Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) to enhance the adhesion at the perovskite/substrate interface using the interactions of ET with perovskites, PTAA and indium tin oxide (ITO) through its multiple function groups. Meanwhile, ET added into perovskites reduces the voids at the bottom perovskite film, due to its capability to tune the crystallization of perovskites by forming adduct with lead. Consequently, the inverted small area F-PSCs achieved an efficiency of 23.4%. The flexible perovskite minimodule with an area of 9 cm 2 achieved an aperture efficiency of ~19.0% certified by National Renewable Energy Laboratory. Furthermore, the optimized unencapsulated flexible minimodule retained 84% of the initial efficiency after 5000 bending cycles and retained 90% of the initial PCE (T90) after light soaking for >750 hours.

14 SOLAR ENERGY↗
DOE OSTI2023

Towards linking lab and field lifetimes of perovskite solar cells

Metal halide perovskite solar cells (PSCs) represent a promising low-cost, thin-film photovoltaic (PV) technology, with unprecedented power conversion efficiencies (PCEs) obtained for both single-junction and tandem applications. To push PSCs toward commercialization, it is critical, albeit challenging, to understand device reliability under real-world outdoor conditions where multiple stress factors (e.g., light, heat, humidity) coexist, generating complicated degradation behaviors. It is necessary to identify accelerated indoor testing protocols - which can correlate specific stressors with observed degradation modes in fielded devices - to quickly guide PSC development. Here, we use a state-of-the-art p-i-n PSC stack (with PCE up to ~25.5%) to show that indoor accelerated stability tests can predict our 6-month outdoor aging tests. Device degradation rates under illumination and at elevated temperatures are most instructive for understanding outdoor device reliability. Further, we also find that the indium tin oxide (ITO)/self-assembled monolayer (SAM)-based hole transport layer (HTL)/perovskite interface most strongly affects our device operation stability. Improving the ion-blocking properties of the SAM HTL increases averaged device operational stability at 50 degree C-85 °C by a factor of ~2.8, reaching over 1000 h at 85 °C and to near 8200 h at 50 °C with a projected 20% degradation, which is among the best to date for high-efficiency p-i-n PSCs.

14 SOLAR ENERGY↗
DOE OSTI2019

Inverted organic solar cells with non-clustering bathocuproine (BCP) cathode interlayers obtained by fullerene doping

Bathocuproine (BCP) is a well-studied cathode interlayer in organic photovoltaic (OPV) devices, where it for standard device configurations has demonstrated improved electron extraction as well as exciton blocking properties, leading to high device efficiencies. For inverted devices, however, BCP interlayers has shown to lead to device failure, mainly due to the clustering of BCP molecules on indium tin oxide (ITO) surfaces, which is a significant problem during scale-up of the OPV devices. In this work, we introduce C70 doped BCP thin films as cathode interlayers in inverted OPV devices. We demonstrate that the interlayer forms smooth films on ITO surfaces, resulting from the introduction of C70 molecules into the BCP film, and that these films possess both improved electron extraction as well exciton blocking properties, as evidenced by electron-only devices and photoluminescence studies, respectively. Importantly, the improved cathode interlayers leads to well-functioning large area (100 mm2) devices, showing a device yield of 100%. This is in strong contrast to inverted devices based on pure BCP layers. These results are founded by the effective suppression of BCP clustering from C70, along with the electron transport and exciton blocking properties of the two materials, which thus presents a route for its integration as an interlayer material towards up-scaled inverted OPV devices.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Plasma-enhanced atomic-layer-deposited gallium nitride as an electron transport layer for planar perovskite solar cells

Low-temperature deposited gallium nitride (GaN) thin-films have been introduced into planar perovskite solar cells (PSCs) as electron transport layers (ETLs) for the first time. Compact and amorphous n-type GaN layers were uniformly coated on fluorine-doped tin oxide (FTO) glass substrates via plasma-enhanced atomic layer deposition (PEALD) technology, in which an optimized deposition temperature of 280 °C was identified and adopted. The as-prepared GaN thin-films were subsequently employed to fabricate planar PSCs with the device configuration FTO/GaN/perovskite/spiro-OMeTAD/Au. Interestingly, although a conduction-band-minimum (CBM) mismatch of 0.59 eV is found at the interface of the 50-PEALD-cycle GaN/perovskite, a significantly enhanced device efficiency from 10.38% to 15.18% has also been achieved relative to the ETL-free PSCs. Meanwhile, the current–voltage hysteresis and device stability of GaN-based PSCs can be remarkably improved. It is found that the GaN layer can promote the electron extraction and reduce recombination at the FTO/perovskite interface. This work demonstrates the feasibility and potential of GaN films as ETLs in planar PSCs.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Low-temperature sprayed SnO x nanocomposite films with enhanced hole blocking for efficient large area perovskite solar cells

Scalable fabrication of charge transport layers with high uniformity and compactness is essential for the commercialization of perovskite solar cells (PSCs). Cost-effective deposition of high-quality electron transport layers (ETLs) is a particularly important step to achieve low-cost, efficient and large-area PSCs. Here, an open-air (relative humidity of 40–50%) and low-temperature (≤100 °C) ultrasonic spray coating of tin oxide (SnO 2 ) nanocomposite films incorporating nanocrystalline SnO 2 nanoparticles in an amorphous SnO x matrix is demonstrated to fabricate large-area ETLs for planar PSCs. The optimized SnO 2 /SnO x nanocomposite exhibits significantly enhanced hole-blocking and high-power conversion efficiencies of 18% and 16% for planar PSCs with an active area of 0.2 cm 2 and 1 cm 2 , respectively. More importantly, the devices show little current–voltage hysteresis as well as good shelf-life stability by maintaining ~90% of the initial performance without encapsulation after 2500 hours storage under inert conditions. Additionally, high voltages of >6.0 V have been obtained for solar modules of 2.1 cm 2 aperture area comprising six sub-cells in series, suggesting that the low-temperature, open-air and fast spray coating is suitable and transferable to deposit large-area charge transport layers for scalable PSCs or other optoelectronic devices.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2025

Electrolytic gold plating, stripping, and ion transport dynamics through a solid-state iodide perovskite

The pronounced electrochemical reactivity between halide perovskites and metal electrodes can introduce mobile extrinsic metal ions which can cause device instability or enable novel functionalities. Here we systematically investigate the kinetics of gold cation (Au + ) migration in indium tin oxide (ITO)/methylammonium lead triiodide (MAPbI 3 )/Au model devices under long-term potentiostatic biasing. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) analyses reveal that Au + ions, electrochemically generated at the Au anode, traverse the perovskite layer with diffusion coefficients on the order of 10 −11 to 10 −10 cm 2 s −1 and are subsequently reduced at the cathode as Au 0 clusters, resembling metal plating behavior in electrolytic cells and solid-state batteries during charging. Furthermore, reversing the applied bias strips the plated Au 0 , revealing reversibility suitable for bipolar resistive switching devices and providing direct evidence of the electrochemical and ionic nature of Au transport within the perovskite matrix. Quantitatively determining diffusion coefficients and ion concentrations provides foundational inputs for future drift-diffusion modelling opportunities and allows us to relate our findings to implications on long term operation of devices like photovoltaic modules. These results clearly demonstrate the solid-state electrochemical nature of perovskite devices, highlight methods to be more quantitative about ion transport properties, provide and emphasize the importance of disentangling electro-, photo-, photoelectrochemical processes for understanding device performance and unlocking new functionalities.

14 SOLAR ENERGY↗
DOE OSTI2026

Hole-transport layer-dependent degradation mechanisms in perovskite solar modules

It is imperative to understand how the design of perovskite solar modules (PSMs) affects their degradation mechanisms and byproducts under environmental stressors to enable their long-term reliability. This work reports on the impact of the hole-transport layer (HTL) on thermal cyclability and degradation mechanisms of p–i–n PSMs by comparing 3 HTLs: NiO x , MeO-2PACz (a self-assembled monolayer), and a bilayer HTL of MeO-2PACz on NiO x . We observe surprising thermal cyclability from a performance standpoint despite generating clear degradation products. We find that without a fully dense HTL, seemingly insignificant moisture/oxygen ingress through the edge of the PSMs can lead to rapid destabilization of the metal halide perovskite (MHP) layer due to reactions between MHP degradation byproducts and the indium-tin oxide layer. We also show that illumination-induced cation phase segregation is dependent on the illumination of an inactive area (regions of the substrate uncovered by the rear electrode). As such, we find that a dense interface between the MHP and ITO is necessary for chemically robust PSMs and highlight criteria for testing field-relevant configurations in lab-scale architectures.

14 SOLAR ENERGY↗
DOE OSTI2019

The role of Mg bulk hyper-doping and delta-doping in low-resistance GaN homojunction tunnel diodes with negative differential resistance

GaN p ++ /n ++ tunnel junctions (TJs) with heavy bulk or delta Mg doping at the junction were grown via molecular beam epitaxy with a hysteresis-free and repeatable negative differential resistance (NDR). The TJ with Mg doping of 5.5 × 10 20 cm -3 shows NDR at~1.8 V and a large current density of 3.4 KA/cm 2 at -1.0 V. Atomic resolution scanning transmission electron microscopy imaging showed no additional defects despite the doping exceeding the solubility limit in GaN allowing subsequent epitaxy of series-connected layers and devices. GaN homojunction TJs grown on bulk GaN showed an improved current density and NDR stability. In addition, the effect of Mg delta doping at the junction was investigated for the first time showing a dramatic improvement in the tunneling characteristics. A metal-organic chemical vapor deposition (MOCVD) grown InGaN light-emitting diode (LED) with an MBE grown GaN homojunction tunnel contact to the MOCVD grown p-GaN layer shows superior lateral conductivity and improved luminescence uniformity, but suffers an added voltage penalty, assumed to be due to interface impurities, compared to control LED with indium-tin-oxide.

Epitaxy↗
DOE OSTI2019

Characterization and analysis of FA x Cs (1- x ) Pb(I y Br (1- y ) ) 3 perovskite solar cells with thickness controlled transport layers for performance optimization

Strong characterization methods are needed to fully comprehend the chemistry and composition of perovskite solar cells. Understanding the interaction between layers inside a cell and how they react with the environment is important to achieve optimum manufacturing processes, and improve efficiency of perovskite solar cells. Here, we probe a hybrid organic-inorganic perovskite cell structure formed by a fluorine-doped tin oxide (FTO), cassiterite (SnO 2 ), mixed halide perovskite, Spiro-OMeTAD and silver layers. We have demonstrated a power conversion efficiency (PCE) greater than 19% and aV oc of more than 1.1 V for a wide-band gap (1.6 eV) perovskite solar cell.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Electric field dynamics in an atmospheric pressure helium plasma jet impinging on a substrate

Time and spatially resolved electric field measurements by Stark polarization spectroscopy in a nanosecond pulsed atmospheric pressure helium jet operating in ambient air and impinging on a conductive indium tin oxide (ITO) coated glass slide are reported. An automatic fitting procedure of the Stark shifted spectra taking into consideration constraints regarding Stark components positions and intensities as well as molecular nitrogen emission subtraction was implemented. This allowed electric field vector components measurements both in the gas phase and at the interface when the jet impinges on the substrate and during the development of a surface ionization wave. The obtained results show an increase of the axial electric field in the jet effluent in the gas phase with a peak magnitude from 12 to 18 kVcm -1 before the ionization wave impinges on the substrate. A steep electric field enhancement to a peak value of about 24 kVcm -1 was observed when the ionization wave impinges on the surface. A peak radial electric field of about 27 kVcm -1 was measured off-axis in the surface ionization wave. These results are consistent with previously reported modelling predictions. While Stark polarization spectroscopy is limited to electric field measurement from regions with emission, we illustrate that the capability to measure near surface electric fields in helium makes it a valuable complementary technique for the electric field-induced second harmonic (E-FISH) technique.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Unveiling the ambipolar carrier transport property of SnO 2–X for multiple-functional interlayers in perovskite solar cells

Tin oxides are the most promising electron transport layers in perovskite solar cells. An ambipolar carrier transport property has been recently demonstrated which enables a simple interconnection structure for all-perovskite tandem solar cells. However, the underlying mechanism for its ambipolar behavior is unclear which cannot be explained by the intrinsic defects in SnO 2-x . Here by using density functional theory calculations, we unveil the origin of the ambipolar carrier transport of non-stoichiometry SnO 2-x with a structure of SnO embedded in SnO 2 matrix. The hybridization of O 2p and Sn 5s orbitals of SnO introduces mid-gap states in the bandgap of SnO 2 , enabling hole transport property for SnO 2-x when x is > 0.2. Increasing the percentage of SnO in SnO 2-x significantly enhances the hole transport capability of SnO 2-x due to the enlarged Sn-O-Sn angles that increases orbital overlapping between O and Sn atoms, thus providing strategies for the further tuning of the carrier transport properties of SnO 2-x by compositional and structural designs.

14 SOLAR ENERGY↗
DOE OSTI2019

Excitation energy-dependent photocurrent switching in a single-molecule photodiode

The direction of electron flow in molecular optoelectronic devices is dictated by charge transfer between a molecular excited state and an underlying conductor or semiconductor. For those devices, controlling the direction and reversibility of electron flow is a major challenge. We describe here a single-molecule photodiode. It is based on an internally conjugated, bichromophoric dyad with chemically linked (porphyrinato)zinc(II) and bis(terpyridyl)ruthenium(II) groups. On nanocrystalline, degenerately doped indium tin oxide electrodes, the dyad exhibits distinct frequency-dependent, charge-transfer characters. Variations in the light source between red-light (∼1.9 eV) and blue-light (∼2.7 eV) excitation for the integrated photodiode result in switching of photocurrents between cathodic and anodic. The origin of the excitation frequency-dependent photocurrents lies in the electronic structure of the chromophore excited states, as shown by the results of theoretical calculations, laser flash photolysis, and steady-state spectrophotometric measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Color-neutral, semitransparent organic photovoltaics for power window applications

Semitransparent organic photovoltaic cells (ST-OPVs) are emerging as a solution for solar energy harvesting on building facades, rooftops, and windows. However, the trade-off between power-conversion efficiency (PCE) and the average photopic transmission (APT) in color-neutral devices limits their utility as attractive, power-generating windows. A color-neutral ST-OPV is demonstrated by using a transparent indium tin oxide (ITO) anode along with a narrow energy gap nonfullerene acceptor near-infrared (NIR) absorbing cell and outcoupling (OC) coatings on the exit surface. The device exhibits PCE = 8.1 ± 0.3% and APT = 43.3 ± 1.2% that combine to achieve a light-utilization efficiency of LUE = 3.5 ± 0.1%. Commission Internationale d’eclairage chromaticity coordinates of (0.38, 0.39), a color-rendering index of 86, and a correlated color temperature of 4,143 K are obtained for simulated AM1.5 illumination transmitted through the cell. Using an ultrathin metal anode in place of ITO, we demonstrate a slightly green-tinted ST-OPV with PCE = 10.8 ± 0.5% and APT = 45.7 ± 2.1% yielding LUE = 5.0 ± 0.3% These results indicate that ST-OPVs can combine both efficiency and color neutrality in a single device.

14 SOLAR ENERGY↗
DOE OSTI2022

Single-beam ion source enhanced growth of transparent conductive thin films

A single-beam ion source was developed and used in combination with magnetron sputtering to modulate the film microstructure. The ion source emits a single beam of ions that interact with the deposited film and simultaneously enhances the magnetron discharge. The magnetron voltage can be adjusted over a wide range, from approximately 240 to 130 V, as the voltage of the ion source varies from 0 to 150 V, while the magnetron current increases accordingly. The low-voltage high-current magnetron discharge enables a 'soft sputtering mode', which is beneficial for thin-film growth. Indium tin oxide (ITO) thin films were deposited at room temperature using a combined single-beam ion source and magnetron sputtering. Furthermore, the ion beam resulted in the formation of polycrystalline ITO thin films with significantly reduced resistivity and surface roughness. Single-beam ion-source-enhanced magnetron sputtering has many potential applications in which low-temperature growth of thin films is required, such as coatings for organic solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Stabilizing the heavily-doped and metallic phase of MoS 2 monolayers with surface functionalization

Monolayer molybdenum disulfide (MoS 2 ) is one of the most studied two-dimensional (2D) transition metal dichalcogenides that is being investigated for various optoelectronic properties, such as catalysis, sensors, photovoltaics, and batteries. One such property that makes this material attractive is the ease in which 2D MoS 2 can be converted between the semiconducting (2H) and metallic/semi-metallic (1T/1T') phases or heavily n-type doped 2H phase with ion intercalation, strain, or excess negative charge. Using n-butyl lithium (BuLi) immersion treatments, we achieve 2H MoS 2 monolayers that are heavily n-type doped with shorter immersion times (10–120 mins) or conversion to the 1T/1T' phase with longer immersion times (6–24 h); however, these doped/converted monolayers are not stable and promptly revert back to the initial 2H phase upon exposure to air. To overcome this issue and maintain the modification of the monolayer MoS 2 upon air exposure, we use BuLi treatments plus surface functionalization p-(CH 3 CH 2 ) 2 NPh-MoS 2 (Et 2 N-MoS 2 )—to maintain heavily n-type doped 2H phase or the 1T/1T' phase, which is preserved for over two weeks when on indium tin oxide or sapphire substrates. We also determine that the low sheet resistance and metallic-like properties correlate with the BuLi immersion times. These modified MoS 2 materials are characterized with confocal Raman/photoluminescence, absorption, x-ray photoelectron spectroscopy as well as scanning Kelvin probe microscopy, scanning electrochemical microscopy, and four-point probe sheet resistance measurements to quantify the differences in the monolayer optoelectronic properties. We will demonstrate chemical methodologies to control the modified monolayer MoS 2 that likely extend to other 2D transition metal dichalcogenides, which will greatly expand the uses for these nanomaterials.

2D TMDC↗
DOE OSTI2024

Effects of transparent conducting electrodes and hole transport layers on the performance of MAPbI 3 solar cells fabricated on PET substrates

Abstract This study investigates how the performance of perovskite solar cells (PSCs) made on polyethylene terephthalate (PET) substrates depends on transparent conducting electrodes (TCEs) and hole transport layers (HTLs). We fabricated PSCs using commercially available PET/TCEs and compared their performance with PSCs manufactured on Glass/indium tin oxide (ITO) substrates. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) with varying levels of acidity and NiO nanoparticles were used as HTLs. The current density-voltage characteristics of PSCs made on PET/TCEs were found to be significantly lower when highly acidic PEDOT:PSS was used as the HTL. However, this was not observed for PSCs made on Glass/ITO. To investigate the interaction between HTL and TCE, atomic force microscopy was carried out after dipping the TCEs in PEDOT:PSS solutions of different acidity. X-ray photoelectron spectroscopy measurements further revealed differences in the chemical composition between ITO film on PET vs. on glass. Our results indicate that the performance of PSCs depends both on the TCE substrates and HTLs, which can be explained by their chemical interaction.

14 SOLAR ENERGY↗
DOE OSTI2020

Probing free carrier plasmons in doped semiconductors using spatially resolved electron energy loss spectroscopy

We report spatially resolved measurements of free carrier collective excitations in a doped semiconductor. Using ~10 meV resolution electron energy loss spectroscopy (EELS) in an electron microscope with Å spatial resolution, we identify both surface and bulk carrier plasmons at infrared energies in a freestanding film of indium tin oxide (ITO). The interference patterns of long wavelength propagating surface carrier plasmons are revealed using spatially resolved EELS, from which we extract a dispersion relation. We further show that the energies of these plasmons vary near the surfaces and grain boundaries of the film due to band bending. Modeling based on dielectric theory agrees very well with experimental results. Finally, carrier plasmons in amorphous and crystalline ITO films are compared. These results should also be helpful for understanding the free carrier plasmons in other doped semiconductors in nanoscale volumes.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗