Surface post‐treatment using ammonium halides effectively reduces large open‐circuit voltage (VOC) losses in bromine‐rich wide‐bandgap (WBG) perovskite solar cells (PSCs). However, the underlying ...mechanism still remains unclear and the device efficiency lags largely behind. Here, a facile strategy of precisely tailoring the phase purity of 2D perovskites on top of 3D WBG perovskite and realizing high device efficiency is reported. The transient absorption spectra, cross‐sectional confocal photoluminescence mapping, and cross‐sectional Kelvin probe force microscopy are combined to demonstrate optimal defect passivation effect and surface electric‐field of pure n = 1 2D perovskites formed atop 3D WBG perovskites via low‐temperature annealing. As a result, the inverted champion device with 1.77‐eV perovskite absorber achieves a high VOC of 1.284 V and a power conversion efficiency (PCE) of 17.72%, delivering the smallest VOC deficit of 0.486 V among WBG PSCs with a bandgap higher than 1.75 eV. This enables one to achieve a four‐terminal all‐perovskite tandem solar cell with a PCE exceeding 25% by combining with a 1.25‐eV low‐bandgap PSC.
Tailoring n = 1 pure 2D perovskites on 3D perovskite surface via low‐temperature phenethylammonium bromide (PEABr) post‐treatment strongly suppresses the defects at the grain boundaries of 3D perovskites, which enables a high open‐circuit voltage of 1.284 V and a low open‐circuit voltage loss of 0.486 V for highly efficient inverted 1.77‐eV wide‐bandgap perovskite solar cells.
Charge carrier mobilities help determine semiconductor performance in optoelectronic applications, but measurement of the individual electron and hole mobilities usually involves indirect methods or ...probes with electrical contacts that are influenced by the quality of the interface or contact. Here, a noncontact method is introduced to distinguish the mobilities of electrons and holes by combining time-resolved terahertz spectroscopy (TRTS) and optical transient reflection (TR) spectroscopy. The validation of this method is first demonstrated on a semi-insulator GaAs wafer, and then, three lead-halide perovskite polycrystalline films with different cation mixtures are studied. We find that the hole mobility is significantly higher (∼10×) than that of the electron mobility in all of the perovskite thin films studied. The highly alloyed triple cation polycrystalline film shows the highest mobility, longest bulk carrier lifetime, and lowest surface recombination velocity.
Light-induced phase segregation, particularly when incorporating bromine to widen the bandgap, presents significant challenges to the stability and commercialization of perovskite solar cells. This ...study explores the influence of hole transport layers, specifically polybis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA) and 4-(3,6-dimethyl-9H-carbazol-9-yl)butylphosphonic acid (Me-4PACz), on the dynamics of phase segregation. Through detailed characterization of the buried interface, we demonstrate that Me-4PACz enhances perovskite photostability, surpassing the performance of PTAA. Nanoscale analyses using in situ Kelvin probe force microscopy and quantitative nanomechanical mapping techniques elucidate defect distribution at the buried interface during phase segregation, highlighting the critical role of substrate wettability in perovskite growth and interface integrity. The integration of these characterization techniques provides a thorough understanding of the impact of the buried bottom interface on perovskite growth and phase segregation.
We report on the fabrication and characterization of polycrystalline Cu 3 SbS 4 thin films grown by magnetron sputtering. We find that Cu 3 SbS 4 thin films deposited at various temperatures show the ...Famatinite structure and high optical absorptions with band gaps of slightly lower than 1.0 eV and weak absorptions centered at about 0.9 eV. The as deposited thin films have very small grains and low carrier density. Sulfurization results in increased hole density, but does not increase the grain size. Due to the film decomposition and sublimation, the deposition and sulfurization are limited to temperatures below 300 °C. Our best small area Cu 3 SbS 4 -based thin-film solar cell shows a conversion efficiency of only 0.46% under AM1.5 illumination. We believe that the small grain size is partially responsible for the poor cell performance.
Inhomogeneous microscopic carrier transport is difficult to study, but important in many condensed-matter applications. For example, the role of grain boundaries (GBs) in polycrystalline ...semiconductors has been controversial for 20 years. In cadmium telluride (CdTe) solar cells, electron-beam-induced current (EBIC) measurements consistently demonstrate enhanced current collection along GBs, which is argued as evidence for interpenetrating CdTe p-n current-collection networks critical to high efficiency. Conversely, cathodoluminescence (CL) measurements consistently indicate that GBs are deleterious low-lifetime regions. Here, we apply transport imaging (TI) in conjunction with spatially correlated EBIC, CL, and scanning Kelvin probe force microscopy measurements to understand carrier drift, diffusion, and recombination in polycrystalline CdTe. We simultaneously observe GB potential wells, reduced carrier lifetime at GBs, and seemingly contradictory enhanced GB current collection, and then describe their coexistence with microscopic TI and physical arguments. The results provide visualization of inhomogeneous transport that is critical to understanding and engineering polycrystalline solar technology.
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Inhomogeneous local carrier transport is critical in polycrystalline semiconductorsVisualize local charge transport inside single grains and across grain boundariesCoexistence of carrier drift, diffusion, and recombination in polycrystalline CdTe
Inhomogeneous local carrier transport is critical in polycrystalline semiconductor applications. Xiao et al. resolve the coexistence with microscopic transport imaging and other physical arguments. The results provide visualization of local charge transport inside individual grains and across grain boundaries, which is critical to understanding and engineering polycrystalline solar technology.
Reduced‐dimensional hybrid perovskite semiconductors have recently attracted significant attention due to their promising stability and optoelectronic properties. However, the issue of poor charge ...transport in 2D perovskites limits its application. Here, studies on intermediate‐controlled crystal growth are reported to improve charge carrier transport in 2D perovskite thin films. It is shown that the coordination strength of solvents with perovskite precursor affects the initial state of intermediate phase formation as well as the subsequent perovskite layer growth. Tuning the solvent composition with a mixture (5:5) of dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO) leads to the growth of highly orientated 2D perovskite films with much‐improved optoelectronic properties (faster transport by ≈50x, longer carrier lifetime by ≈4x, and lower defect density by ≈30x) than the film prepared with pure DMF. Consequently, perovskite solar cells based on DMF/DMSO (5:5) show >80% efficiency improvement than the devices based on pure DMF.
Here, intermediate‐controlled crystal growth is reported via solvent tuning to prepare highly oriented 2D perovskite films with faster transport, longer carrier lifetime, and lower defect density.
Chiral‐induced spin selectivity is recently demonstrated in a range of spin‐dependent optoelectronics and electrochemistry. Herein, a new type of amorphous chiral tartaric acid‐FeNi coordination ...polymer fabricated by electrodeposition methods, achieving both high spin‐polarization and high electrocatalytic activity for oxygen evolution, is reported. Circular dichroism shows signature optical activity from the coordination polymer. Conductive atomic force microscopy measurements demonstrate a high spin polarization through the chiral electrocatalyst, which significantly suppresses the formation of hydrogen peroxide byproducts compared to the achiral ones. These chiral Fe‐Ni electrocatalysts exhibit a low overpotential of 205 and 280 mV to achieve 10 and 100 mA cm−2, respectively.
This study demonstrates a new type of chiral Fe‐Ni electrocatalyst for enhanced oxygen evolution reaction (OER) through spin control by chiral‐induced spin selectivity. A high spin‐polarized current is generated in chiral electrocatalyst that suppresses the formation of H2O2 byproduct. Chiral catalyst shows a low OER overpotential and exhibits a 35% increase of current density compared to the achiral ones.
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