Sn-Pb Mixed Perovskites with Fullerene-Derivative Interlayers for Efficient Four-Terminal All-Perovskite Tandem Solar Cells

Interfacial engineering is the key to high-performance perovskite solar cells (PSCs). While a wide range of fullerene interlayers are investigated for Pb-based counterparts with a bandgap of >1.5 eV, the role of fullerene interlayers is barely investigated in Sn-Pb mixed narrow-bandgap (NBG) PSCs. In this work, two novel solution-processed fullerene derivatives are investigated, namely indene-C60-propionic acid butyl ester and indene-C60-propionic acid hexyl ester (IPH), as the interlayers in NBG PSCs. It is found that the devices with IPH-interlayer show the highest performance with a remarkable short-circuit current density of 30.7 mA cm−2 and a low deficit in open-circuit voltage. The reduction in voltage deficit down to 0.43 V is attributed to reduced non-radiative recombination that the authors attribute to two aspects: 1) a higher conduction band offset of ≈0.2 eV (>0 eV) that hampers charge-carrier-back-transfer recombination; 2) a decrease in trap density at the perovskite/interlayer/C60 interfaces that results in reduced trap-assisted recombination. In addition, incorporating the IPH interlayer enhances charge extraction within the devices that results in considerable enhancement in short-circuit current density. Using a NBG device with an IPH interlayer, a respectable power conversion efficiency of 24.8% is demonstrated in a four-terminal all-perovskite tandem solar cell

Nanostructured front electrodes for perovskite/c-Si tandem photovoltaics

The rise in the power conversion efficiency (PCE) of perovskite solar cells has triggered enormous interest in perovskite-based tandem photovoltaics. One key challenge is to achieve high transmission of low energy photons into the bottom cell. Here, nanostructured front electrodes for 4-terminal perovskite/crystalline-silicon (perovskite/c-Si) tandem solar cells are developed by conformal deposition of indium tin oxide (ITO) on self-assembled polystyrene nanopillars. The nanostructured ITO is optimized for reduced reflection and increased transmission with a tradeoff in increased sheet resistance. In the optimum case, the nanostructured ITO electrodes enhance the transmittance by ∼7% (relative) compared to planar references. Perovskite/c-Si tandem devices with nanostructured ITO exhibit enhanced short-circuit current density (2.9 mA/cm2 absolute) and PCE (1.7% absolute) in the bottom c-Si solar cell compared to the reference. The improved light in-coupling is more pronounced for elevated angle of incidence. Energy yield enhancement up to ∼10% (relative) is achieved for perovskite/c-Si tandem architecture with the nanostructured ITO electrodes. It is also shown that these nanostructured ITO electrodes are also compatible with various other perovskite-based tandem architectures and bear the potential to improve the PCE up to 27.0%

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8_{0.8}MA0.2_{0.2}Sn0.5_{0.5}Pb0.5_{0.5}I3_{3}) for All‐Perovskite Tandem Solar Cells

All-perovskite multijunction photovoltaics, combining a wide-bandgap (WBG) perovskite top solar cell (EG ≈1.6–1.8 eV) with a low-bandgap (LBG) perovskite bottom solar cell (EG 33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum-assisted growth control (VAGC) of solution-processed LBG perovskite thin films based on mixed Sn–Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well-established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge-carrier lifetime. The improved optoelectronic characteristics enable high-performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four-terminal all-perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active-area solar cells up to 1 cm²

Spontaneous Enhancement of the Stable Power Conversion Efficiency in Perovskite Solar Cells

The power conversion efficiency (PCE) of lead-halide perovskite solar cells (PSCs) is reported to increase over a period of days after their fabrication while they are stored in dark. Thus far, effects underlying this spontaneous enhancement are not understood. This work investigates the phenomenon for a variety of multi-cation-halide PSCs with different perovskite compositions and architectures. The observations reveal that spontaneous enhancement is not restricted to specific charge- transport layers or perovskite compositions. The highest PCE observed in this study is the enhanced stable PCE of 19% (increased by 4% absolute). An increased open-circuit voltage is the primary contributor to the improved efficiency. Using time-resolved photoluminescence measurements, initially-present low-energy states are identified that disappear over a storage period of a few days. Furthermore, trap states probed by thermally stimulated current technique exist in pristine PSCs and strikingly decrease for stored devices. In addition, ideality factor approaches unity and X-ray diffraction analyses show a lattice strain relaxation over the same period of time. These observations indicate that spontaneous enhancement of the PSCs is based on a reduction in trap-assisted non-radiative recombination possibly due to strain relaxation. Considering the demonstrated generality of spontaneous enhancement for different compositions of multi-cation-halide PSCs, our results highlight the importance of determining absolute PCE increase initiated by spontaneous enhancement for developing high-efficiency PSCs

Scalable two-terminal all-perovskite tandem solar modules with a 19.1% efficiency

Monolithic all-perovskite tandem photovoltaics promise to combine low-cost and high-efficiency solar energy harvesting with the advantages of all-thin-film technologies. To date, laboratory-scale all-perovskite tandem solar cells have only been fabricated using non-scalable fabrication techniques. In response, this work reports on laser-scribed all-perovskite tandem modules processed exclusively with scalable fabrication methods (blade coating and vacuum deposition), demonstrating power conversion efficiencies up to 19.1% (aperture area, 12.25 cm2; geometric fill factor, 94.7%) and stable power output. Compared to the performance of our spin-coated reference tandem solar cells (efficiency, 23.5%; area, 0.1 cm2), our prototypes demonstrate substantial advances in the technological readiness of all-perovskite tandem photovoltaics. By means of electroluminescence imaging and laser-beam-induced current mapping, we demonstrate the homogeneous current collection in both subcells over the entire module area, which explains low losses (<5%rel) in open-circuit voltage and fill factor for our scalable modules

Spectral Dependence of Degradation under Ultraviolet Light in Perovskite Solar Cells

Perovskite solar cells (PSCs) demonstrate excellent power conversion efficiencies (PCEs) but face severe stability challenges. One key degradation mechanism is exposure to ultraviolet (UV) light. However, the impact of different UV bands is not yet well established. Here, we systematically study the stability of PSCs on the basis of a methylammonium lead iodide (CH₃NH₃PbI₃) absorber exposed to (i) 310–317 (UV-B range) and (ii) 360–380 nm (UV-A range), under accelerated conditions. We demonstrate that the investigated UV-B band is detrimental to the stability of PSCs, resulting in PCE degradation by more than 50% after an exposure period >1700 sun-hours. This finding is valid for architectures with a range of electron transport layers, including SnO₂, compact-TiO₂, electron-beam TiO₂, and nanoparticle-TiO₂. We also show that photodegradation is apparent for high, as well as for low illumination intensities of UV-B light, but not for illumination with UV-A wavelengths. Finally, we show that degradation of PSCs is preventable at the cost of a small fraction of photocurrent by using UV-filtering or luminescent downshifting layers

Photovoltaic Devices: Electron‐Beam‐Evaporated Nickel Oxide Hole Transport Layers for Perovskite‐Based Photovoltaics (Adv. Energy Mater. 12/2019)

High‐quality inorganic charge extraction layers are of key importance for efficient and stable perovskite‐based photovoltaics. In article number 1802995, Tobias Abzieher, Ulrich W. Paetzold, and co‐workers introduce oxygen‐assisted electron beam evaporation of NiOx as a promising approach for the fabrication of highly transparent hole transport layers. By integrating these layers in inkjet‐printed and all‐evaporated perovskite solar cells, record PCEs are achieved

Electron Beam Evaporated Nickel Oxide Hole Transport Layers for Perovskite Based Photovoltaics

High amp; 8208;quality charge carrier transport materials are of key importance for stable and efficient perovskite amp; 8208;based photovoltaics. This work reports on electron amp; 8208;beam amp; 8208;evaporated nickel oxide NiOx layers, resulting in stable power conversion efficiencies PCEs of up to 18.5 when integrated into solar cells employing inkjet amp; 8208;printed perovskite absorbers. By adding oxygen as a process gas and optimizing the layer thickness, transparent and efficient NiOx hole transport layers HTLs are fabricated, exhibiting an average absorptance of only 1 . The versatility of the material is demonstrated for different absorber compositions and deposition techniques. As another highlight of this work, all amp; 8208;evaporated perovskite solar cells employing an inorganic NiOx HTL are presented, achieving stable PCEs of up to 15.4 . Along with good PCEs, devices with electron amp; 8208;beam amp; 8208;evaporated NiOx show improved stability under realistic operating conditions with negligible degradation after 40 h of maximum power point tracking at 75 C. Additionally, a strong improvement in device stability under ultraviolet radiation is found if compared to conventional perovskite solar cell architectures employing other metal oxide charge transport layers e.g., titanium dioxide . Finally, an all amp; 8208;evaporated perovskite solar mini amp; 8208;module with a NiOx HTL is presented, reaching a PCE of 12.4 on an active device area of 2.3 cm

Temperature Variation-Induced Performance Decline of Perovskite Solar Cells

This paper reports on the impact of outdoor temperature variations on the performance of organo metal halide perovskite solar cells (PSCs). It shows that the open-circuit voltage (<i>V</i>_OC) of a PSC decreases linearly with increasing temperature. Interestingly, in contrast to these expected trends, the current density (<i>J</i>_SC) of PSCs is found to decline strongly below 20% of the initial value upon cycling the temperatures from 10 to 60 °C and back. This decline in the current density is driven by an increasing series resistance and is caused by the fast temperature variations as it is not apparent for solar cells exposed to constant temperatures of the same range. The effect is fully reversible when the devices are kept illuminated at an open circuit for several hours. Given these observations, an explanation that ascribes the temperature variation-induced performance decline to ion accumulation at the contacts of the solar cell because of temperature variation-induced changes of the built-in field of the PSC is proposed. The effect might be a major obstacle for perovskite photovoltaics because the devices exposed to real outdoor temperature profiles over 4 h showed a performance decline of >15% when operated at a maximum power point

MDF treatment with a Dielectric Barrier Discharge (DBD) torch

International audienceA Dielectric Barrier Discharge (DBD) torch has been designed for the treatment of several wood species and composites. This paper presents some results obtained onto Medium Density Fiberboard (MDF) samples. The aim of the treatments was to improve their wetting properties. Tests made before and after treatments showed improvements of surface wetting and have been correlated with surface chemical composition. It also has been shown that the treatment effect is ephemeral