Halide Perovskite Absorbers Research Articles

Strain Heterogeneity and Extended Defects in Halide Perovskite Devices.

Strain is an important property in halide perovskite semiconductors used for optoelectronic applications because of its ability to influence device efficiency and stability. However, descriptions of strain in these materials are generally limited to bulk averages of bare films, which miss important property-determining heterogeneities that occur on the nanoscale and at interfaces in multilayer device stacks. Here, we present three-dimensional nanoscale strain mapping using Bragg coherent diffraction imaging of individual grains in Cs0.1FA0.9Pb(I0.95Br0.05)3 and Cs0.15FA0.85SnI3 (FA = formamidinium) halide perovskite absorbers buried in full solar cell devices. We discover large local strains and striking intragrain and grain-to-grain strain heterogeneity, identifying distinct islands of tensile and compressive strain inside grains. Additionally, we directly image dislocations with surprising regularity in Cs0.15FA0.85SnI3 grains and find evidence for dislocation-induced antiphase boundary formation. Our results shine a rare light on the nanoscale strains in these materials in their technologically relevant device setting.

Enhanced radiation hardness of lead halide perovskite absorber materials via incorporation of Dy2+ cations

Continuously growing evidence of the excellent radiation hardness of perovskite solar cells stimulates their intense exploration in the context of potential aerospace applications. However, there is still a very limited understanding of the fundamental aspects such as the mechanisms of the interaction of complex lead halides with different types of ionizing radiation and associated aging pathways, even though this knowledge is essentially important for the development of new materials with improved properties. Herein, we made one of the first steps to fill this gap through a systematic study of the aging behavior of two perovskite absorber materials under exposure to three different stressors: 60Co gamma-rays, 8.5 MeV electron fluences, and light. The application of a set of complementary spectroscopy and microscopy techniques allowed us to identify and compare perovskite degradation pathways caused by each type of the ionizing radiation. In particular, radiation-induced phase segregation with the formation of δ-phases of CsPbI3 and FAPbI3 appears to be a common route in the case of double cation perovskites. Most importantly, we have revealed that the incorporation of dysprosium cations as a replacement of 1 % of Pb2+ ions in the Cs0.12FA0.88Pb0.99Dy0.01I3 material formulation results in a remarkably improved radiation hardness: this modification blocks the formation of metallic lead and strongly suppresses segregation of Cs-rich and FA-rich phases in perovskite films under exposure to gamma rays or high-energy electrons. Thus, these results open up a promising research direction for designing radiation-resistant perovskite absorbers through rational compositional engineering.

Interface defect formation for atomic layer deposition of SnO2 on metal halide perovskites

With the rapidly advancing perovskite solar cell (PSC) technology, dedicated interface engineering is critical for improving device stability. Atomic layer deposition (ALD) grown metal oxide films have drawn immense attention for the fabrication of stable PSC. Despite the advantages of ALD, the deposition of metal oxides directly on bare perovskite has so far not been achieved without damaging the perovskite layer underneath. In addition, the changes to the physicochemical and electronic properties at the perovskite interface upon exposure to the ALD precursors can alter the material and hence device functionality. Herein, we report on a synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES) investigation of the interface between metal halide perovskite (MHP) absorber and ALD-SnO2 electron transport layer. We find clear evidence for the formation of new chemical species (nitrogen compound, lead dihalides) and an upward band bending in the MHP and downward band bending in the SnO2 towards the MHP/ALD-SnO2 interface. The upward bending at the interface forms an electron barrier layer of ∼400 meV, which is detrimental to the PSC performance. In addition, we assess the effectiveness of introducing a thin interlayer of the organic electron transport material Phenyl-C61-butyric acid methyl ester (PCBM) between MHP and ALD-SnO2 to mitigate the effects of ALD deposition.

Recent progress in monolithic two-terminal perovskite-based triple-junction solar cells

Monolithic perovskite-based triple junction solar cells have the potential to surpass the power conversion efficiency (PCE) limits of single and dual-junction solar cells.

Integration of Large-Area Halide Perovskite Single Crystals and Substrates via Chemical Welding Using an Ionic Liquid for Applications in X-ray Detection.

The large carrier lifetime mobility product and strong stopping power for high-energy X-rays make halide perovskites an attractive candidate for next-generation X-ray detectors. In particular, high-energy X-rays in the range of several tens of keV require halide perovskite absorber layers with thicknesses exceeding a few millimeters. To avoid carrier scattering caused by grain boundaries at such thicknesses, the utilization of single crystals is desirable. Large-area single crystals are predominantly grown in a freestanding form, and integration onto a substrate is necessary for the fabrication of commercial devices. However, an effective method for integrating large single crystals onto a substrate has not yet been developed. In this study, a large-area (20 cm2) MAPbBr3 single crystal is bonded to an indium tin oxide (ITO) substrate using an ionic liquid, showing strong adhesion strength of 164 kPa. X-ray detectors based on ITO/MAPbBr3 single crystal bonded by methylammonium acetate achieved excellent sensitivity of 91,200 μC Gyair-1 cm-2, the highest among substrate-integrated halide perovskite single crystal X-ray detectors.

Facile synthesis of MAPbI3/CNTs composites with superior electromagnetic wave absorption performances

Perovskite shines as a top contender in the realm of electromagnetic waves (EMW) absorption, owing to its unique physical properties, structural characteristics, and multifunctionality. However, it is still a huge challenge to synthesize high-performance EMW absorbing perovskite materials with environmental-friendly and sustainable processes, despite the simplicity of the perovskite preparation procedures. To address this issue, a facile solvent-free method was developed in this study for CH3NH3PbI3 (MAPbI3), then introduced carbon nanotubes (CNTs) and subsequently prepared MAPbI3/CNTs (MC) composites using a simple procedure. The frequency, thickness, reflection loss (RL), and effective absorption bandwidth (EAB) of MC for EMW absorption were systematically investigated by adjusting the filling amount and component ratio of MC. It is interesting to find that the as-prepared MC composites always achieve high absorption intensities in X and Ku bands. Moreover, an appropriate amount of CNTs can further optimize the impedance matching of MC and promote the loss capability of MAPbI3.With a loading ratio of 25 wt% and a mass ratio of 2:1 between MAPbI3 and CNTs, the MC sample exhibits excellent absorption capability, achieving the lowest RL of −63.8 dB at 1.8 mm and the maximum EAB of 5.16 GHz at 1.69 mm. These findings contribute to the design and development of organic-inorganic halide perovskite absorbers with superior EMW absorption performances.

Optimized High-Efficiency Solar Cells with Dual Hybrid Halide Perovskite Absorber Layers

Optimized High-Efficiency Solar Cells with Dual Hybrid Halide Perovskite Absorber Layers

Surface Modulation via Conjugated Bithiophene Ammonium Salt for Efficient Inverted Perovskite Solar Cells.

The metal halide perovskite absorbers are prone to surface defects, which severely limit the power conversion efficiencies (PCEs) and the operational stability of the perovskite solar cells (PSCs). Herein, trace amounts of bithiophene propylammonium iodide (bi-TPAI) are applied to modulate the surface properties of the gas-quenched perovskite. It is found that the bi-TPAI surface treatment has negligible impact on the perovskite morphology, but it can induce a defect passivation effect and facilitate the charge carrier extraction, contributing to the gain in the open-circuit voltage (Voc) and fill factor. As a result, the PCE of the gas-quenched sputtered NiOx-based inverted PSCs is enhanced from the initial 20.0% to 22.0%. Most importantly, the bi-TPAI treatment can largely alleviate or even eliminate the burn-in process during the maximum power point tracking measurement, improving the operational stability of the devices.

Development of MnxCo0.015Zn1-xO electron transport layer for perovskite solar cells: Experimental and simulation study

The electron transport layer (ETL) plays an important role in the performance and stability enhancement of perovskite solar cells (PSCs). Zinc oxide is considered a cost-effective and low-temperature processed ETL for PSCs, which offers decent mobility. However, the interface reaction occurs via a reaction of zinc oxide with the organic-inorganic metal hybrid halide perovskite absorber, which results in the degradation of the PSCs. To overcome this issue, metal doping was carried out. However, metal doping causes a reduction in the transmittance of the zinc oxide ETL layer because of high absorption. Thus, the overall performance of the PSCs was reduced due to the lessening of the photogenerated current. In this regard metal co-doping (Mn and Co) was done to improve the electrical as well as electronic properties. Furthermore, the influence of Mn doping on the structural, optical, and photoluminescence properties of MnxCo0.015Zn1-xO (x = 0, 0.002, 0.008, and 0.012) hexagonal nanosheets was investigated. X-ray diffraction results revealed that the inter-planar spacing, cell parameters, unit cell volume, lattice strain, and dislocation density were maximum for the Mn content of 0.2%. The acquired values of the optical band gap (Eg) are 3.39, 3.52, 3.58, and 3.18 eV for x = 0, 0.2%, 0.8%, and 1.2%, respectively. The corresponding absorption coefficient is reduced with increasing Mn content. The obtained refractive indices are 1.437, 1.402, 1.428, and 1.426 for x = 0, 0.2, 0.8, and 1.2%, respectively. The above results confirm that the MnxCo0.015Zn1-xO with x = 0.8% provides the lowest absorption and the highest value of bandgap. Thus, it can be the most suitable ETL for high-performance PSCs. The simulation results reveal that via applying MCZO ETL, the efficiency can be achieved over 23%.

Recent Progress in Perovskite Tandem Solar Cells.

Tandem solar cells are widely considered the industry's next step in photovoltaics because of their excellent power conversion efficiency. Since halide perovskite absorber material was developed, it has been feasible to develop tandem solar cells that are more efficient. The European Solar Test Installation has verified a 32.5% efficiency for perovskite/silicon tandem solar cells. There has been an increase in the perovskite/Si tandem devices' power conversion efficiency, but it is still not as high as it might be. Their instability and difficulties in large-area realization are significant challenges in commercialization. In the first part of this overview, we set the stage by discussing the background of tandem solar cells and their development over time. Subsequently, a concise summary of recent advancements in perovskite tandem solar cells utilizing various device topologies is presented. In addition, we explore the many possible configurations of tandem module technology: the present work addresses the characteristics and efficacy of 2T monolithic and mechanically stacked four-terminal devices. Next, we explore ways to boost perovskite tandem solar cells' power conversion efficiencies. Recent advancements in the efficiency of tandem cells are described, along with the limitations that are still restricting their efficiency. Stability is also a significant hurdle in commercializing such devices, so we proposed eliminating ion migration as a cornerstone strategy for solving intrinsic instability problems.

Incorporation of carbon nanotubes in hole transport materials for perovskite solar cells

ABSTRACT Many loss processes in perovskite solar cells (PSCs) take place at interfaces. One effective mitigation strategy is introducing carbon derivatives at the interface of the charge transport layers with the halide perovskite absorber and/or with the contacts. In this work, single-walled carbon nanotubes are incorporated into the hole transporting material (HTM), either as composites or as a separate layer on top of the HTM. Both organic and inorganic hole transport materials are studied to validate this approach for different types of HTMs. It is shown that the CNTs facilitate charge transport from perovskite to the back contact, regardless of the HTM used. The use of CNTs results in an increase in a significant increase in short circuit current and power conversion efficiency. This study illustrates how SWCNTs can be utilised to improve the properties of a wide range of HTMs, which will pave the way for more efficient and PSCs.

Design and Simulation of Cs2BiAgI6 Double Perovskite Solar Cells with Different Electron Transport Layers for Efficiency Enhancement

Lead-free Cs2BiAgI6 has garnered a lot of research interest recently due to its suitability as a potential absorber layer in the solar cell (SC) architecture owing to its low cost, good stability, and high efficiency. The main highlight of this research work includes the photovoltaic (PV) performance enhancement of Cs2BiAgI6 double perovskite solar cells (PSCs) by optimizing the optoelectronic parameters of the absorber, electron transport layer (ETL), hole transport layer (HTL), and various interface layers. Solar Cell Capacitance Simulator One dimension (SCAPS-1D) numerical simulation was used to optimize the performance of Cs2BiAgI6 absorber-based SCs consisting of copper barium thiostannate (CBTS) as the HTL and TiO2, PCBM, ZnO, IGZO, SnO2, and WS2 as ETLs. The role of the non-lead cesium-based halide perovskite absorber layer in the improvement of the SC performance was systematically investigated through a variation in the thickness, doping density, and defect density of the absorber layer, ETL, and HTL. The performance of the investigated device architectures is largely dependent on the thickness of the absorber layer, acceptor density, defect density, and the combination of different ETLs and HTLs. We found that TiO2, PCBM, ZnO, IGZO, SnO2, and WS2 ETL-based optimized devices recorded a power conversion efficiency (PCE) of 23.14, 23.71, 23.69, 22.97, 23.61, and 21.72%, respectively. Furthermore, the effect of series and shunt resistances, temperature, capacitance, and Mott–Schottky for the six optimized devices was estimated along with the computation of the corresponding generation and recombination rates, current density–voltage (J–V), and quantum efficiency (QE) characteristics. The PV parameters obtained from this comprehensive analysis are finally compared with the earlier published theoretical and experimental reports on Cs2BiAgI6 absorber-based SCs.

Efficient Inverted Perovskite Solar Cells with a Fill Factor Over 86% via Surface Modification of the Nickel Oxide Hole Contact

AbstractThe poor interface quality between nickel oxide (NiOx) and halide perovskites limits the performance and stability of NiOx‐based perovskite solar cells (PSCs). Here a reactive surface modification approach based on the in situ decomposition of urea on the NiOx surface is reported. The pyrolysis of urea can reduce the high‐valence state of nickel and replace the adsorbed hydroxyl group with isocyanate. Combining theoretical and experimental analyses, the treated NiOx films present suppressed surface states and improved transport energy level alignment with the halide perovskite absorber. With this strategy, NiOx‐based PSCs achieve a champion power conversion efficiency (PCE) of 23.61% and a fill factor of over 86%. The device's efficiency remains above 90% after 2000 h of thermal aging at 85 °C. Furthermore, perovskite solar modules achieve PCE values of 18.97% and 17.18% for areas of 16 and 196 cm2, respectively.

Organic ammonium iodide salts as passivation for buried interface enables efficient and stable NiOx based p-i-n perovskite solar cells

The interfaces between a halide perovskite absorber film and its charge transporting layers have been identified as one of the key bottlenecks for achieving high performance and stability.

Growth of single-crystalline MAPbI3 perovskite film by a modified space-confined inverse temperature crystallization method

Single crystalline (SC) metal halide perovskite absorber film can outperform its polycrystalline counterpart in power conversion efficiency and stability due to the absence of grain boundaries. However, SC perovskite film's direct growth on charge selective contact layer coated substrates for solar cell applications is not widely explored. In this study, SC methylammonium lead iodide (MAPbI3) perovskite film is directly grown on charge selective (electron and hole transport) contact layer coated substrates (TiO2 coated fluorine doped tin oxide (FTO) glass substrate and poly(triarylamine) (PTAA) coated indium tin oxide (ITO) glass substrate) by inverse temperature crystallization (ITC) method. The PTAA/ITO substrate's hydrophobic nature led to faster ion migration and controlled nucleation, resulting in large-sized SC MAPbI3 perovskite film. X-ray diffraction of the MAPbI3/PTAA/ITO showed SC nature with diffraction from (200) and (400) planes, indicating that the film is majorly (100) oriented. The MAPbI3 film grown on TiO2/FTO is found to be relatively small in size (< 1 mm), majorly oriented in the (110) plane with diffraction also from other planes indicating polycrystalline nature. Long-term stability studies over 1500 h show that SC MAPbI3 films show more endurance to ambient conditions than polycrystalline MAPbI3. The growth time of 50 h was reduced to 30 h by employing antisolvent-assisted ITC, resulting in ultra-stable circular shaped films suitable for photovoltaic applications.

(Invited) Opportunities and Challenges for GW Scale Perovskite PV Manufacturing

Halide perovskite absorber materials offer a viable pathway for developing photovoltaic (PV) technology at GW levels because of their superior optoelectronic properties and low-temperature solution process ability. Despite the exciting progress and extraordinary potentials, the commercialization of this emerging technology still faces serious challenges. In this talk, I will discuss the opportunities and challenges for GW scale perovskite PV manufacturing.

(Invited) Monolithic All-Perovskite Tandem Cells for Unassisted Water Splitting

The past decade has witnessed a rapid evolution of research on metal halide perovskite-based optoelectronic and energy devices. In light of this remarkable progress, photoelectrochemical (PEC) cells based on halide perovskite photoabsorbers have recently emerged as a promising solar fuel technology. Notably, the bandgap tunability and low-temperature processing make monolithic all-perovskite tandem cells ideal candidates for achieving efficient, cost-effective, unassisted solar-driven water electrolysis devices.Here, we report our progress on fabricating monolithic all-perovskite tandem cells consisting of two solution-processed perovskite subcells for unassisted water-splitting applications. The all-perovskite tandem devices are achieved by monolithically integrating a wide-bandgap (1.7 – 2.1 eV) Pb-based mixed-halide (Br-I) perovskite top subcell and a narrower-bandgap (1.25 - 1.55 eV) bottom subcell based on Pb-based or mixed Pb-Sn iodide perovskites. Varying the halide perovskite composition for each subcell enables us to tailor the photovoltaic performance of the tandem devices. We demonstrate that all-perovskite tandem devices with various bandgap compositions can deliver open-circuit voltages of more than 2 V. The high photovoltage provides a sufficient overpotential to drive unassisted PEC water splitting with a solar-to-hydrogen conversion efficiency of more than 10%. Additionally, we show that proper water-impermeable encapsulants are needed to prevent degradation of the halide perovskite absorbers in an aqueous environment and enable a long operational lifetime.

Steady-state optoelectronic measurements of halide perovskites on a selective contact: a path to in-depth comprehension of their photovoltaic activity

Most of the charge transport properties in halide perovskite (HaP) absorbers are measured by transient measurements with pulsed excitations; however, most solar cells in real life function in steady-state conditions. In contrast to working devices that include selective contacts, steady-state measurements need as high as possible photoconductivity (σph), which is typically restricted to the absorber alone. In this paper, we enabled steady-state charge transport measurement using atomic layer deposition (ALD) to grow a conformal, ultra-thin (∼4 nm) ZnO electron transport layer that is laterally insulating due to its thickness. Due to the highly alkaline behavior of the ZnO surfaces, it readily reacts with halide Perovskites. ALD process was used to form an Aluminum oxynitride (AlON) thin (∼2 nm) layer that passivates the ZnO-HaP interface. We show that the presence of the AlON layer prevents HaP degradation caused by the interaction with the ZnO layer, improves the HaP σph, and doubles the HaP carrier diffusion lengths.

Photo Stabilization of p-i-n Perovskite Solar Cells with Bathocuproine: MXene.

Interface engineering is one of the promising strategies for the long-term stabilization of perovskite solar cells (PSCs), preventing chemical decomposition induced by external agents and promoting fast charge transfer. Recently, MXenes-2D structured transition metal carbides and nitrides with various functionalization (O, -F, -OH) have demonstrated high potential for mastering the work function in halide perovskite absorbers and have significantly improved the n-type charge collection in solar cells. This work demonstrates that MXenes allow for efficient stabilization of PSCs besides improving their performances. A mixed composite bathocuproine:MXene, that is, (BCP:MXene) interlayer, is introduced at the interface between an electron-transport layer (ETL) and a metal cathode in the p-i-n device structure. The investigation demonstrates that the use of BCP:MXene interlayer slightly increases the power conversation efficiency (PCE) for PSCs (from 16.5 for reference to 17.5%) but dramatically improves the out of Glove-Box stability. Under ISOS-L-2 light soaking stress at 63 ± 1.5°C, the T80 (time needed to reduce efficiency down to 80% of the initial one) period increases from 460to > 2300hours (h).

Wide bandgap halide perovskite absorbers for semi-transparent photovoltaics: from theoretical design to modules

Wide bandgap halide perovskite absorbers for semi-transparent photovoltaics: from theoretical design to modules