Suppression Of Nonradiative Recombination Research Articles

Performance Enhancement of Hole Transport Layer-Free Carbon-Based CsPbIBr2 Solar Cells through the Application of Perovskite Quantum Dots.

CsPbIBr2, with its suitable bandgap, shows great potential as the top cell in tandem solar cells. Nonetheless, its further development is hindered by a high defect density, severe carrier recombination, and poor stability. In this study, CsPbI1.5Br1.5 quantum dots were utilized as an additive in the ethyl acetate anti-solvent, while a layer of CsPbBr3 QDs was introduced between the ETL and the CsPbIBr2 light-harvester film. The combined effect of these two QDs enhanced the nucleation, crystallization, and growth of CsPbIBr2 perovskite, yielding high-quality films characterized by an enlarged crystal size, reduced grain boundaries, and smooth surfaces. And a wider absorption range and better energy band alignment were achieved owing to the nano-size effect of QDs. These improvements led to a decreased defect density and the suppression of non-radiative recombination. Additionally, the presence of long-chain organic molecules in the QD solution promoted the formation of a hydrophobic surface, significantly enhancing the long-term stability of CsPbIBr2 PSCs. Consequently, the devices achieved a PCE of 9.20% and maintained an initial efficiency of 85% after 60 days of storage in air. Thus, this strategy proves to be an effective approach for the preparation of efficient and stable CsPbIBr2 PSCs.

Enhancing photovoltaic performance and stability of inverted perovskite solar cells via multifunctional molecular additive

The film quality of perovskite absorber plays a fundamental role in determining the efficiency and stability of perovskite solar cells (PSCs), of which high crystallinity and low defect density are consistently persuaded. Here, a strategy using multifunctional additive of N,N′-Diallyl-L-tartardiamide (NDT) to produce high-quality perovskite film is proposed. The rich coordination and hydrogen bonding between NDT and perovskite effectively passivate trap states, improve film crystallinity, stabilize perovskite crystal structure and confine ions migration, resulting in enhancement of charge transport and suppression of nonradiative recombination. Consequently, compared with the control device (19.07 %), the NDT-modified devices achieve a champion efficiency of 21.71 % with negligible hysteresis as well as excellent air and light stability. This work presents a facile and effective approach via multifunctional molecular additive to achieve high-performance inverted (p-i-n) PSCs.

Perovskite/silicon tandem solar cells with bilayer interface passivation.

Two-terminal monolithic perovskite/silicon tandem solar cells demonstrate huge advantages in power conversion efficiency compared with their respective single-junction counterparts1,2. However, suppressing interfacial recombination at the wide-bandgap perovskite/electron transport layer interface, without compromising its superior charge transport performance, remains a substantial challenge for perovskite/silicon tandem cells3,4. By exploiting the nanoscale discretely distributed lithium fluoride ultrathin layer followed by an additional deposition of diammonium diiodide molecule, we have devised a bilayer-intertwined passivation strategy that combines efficient electron extraction with further suppression of non-radiative recombination. We constructed perovskite/silicon tandem devices on a double-textured Czochralski-based silicon heterojunction cell, which featured a mildly textured front surface and a heavily textured rear surface, leading to simultaneously enhanced photocurrent and uncompromised rear passivation. The resulting perovskite/silicon tandem achieved an independently certified stabilized power conversion efficiency of 33.89%, accompanied by an impressive fill factor of 83.0% and an open-circuit voltage of nearly 1.97 V. To the best of our knowledge, this represents the first reported certified efficiency of a two-junction tandem solar cell exceeding the single-junction Shockley-Queisser limit of 33.7%.

Synergistic passivation and energy level alignment by graphene quantum dots for high performance inverted CsPbI3 perovskite solar cells

Inorganic CsPbI3 perovskite solar cells (PSCs) have garnered considerable attention due to their high thermal stability and promising application in tandem devices. However, further advancement of the performance of CsPbI3 PSCs is restricted by severe nonradiative recombination, which is related to substantial defects and mismatched energy levels. Herein, the versatile graphene quantum dots (GQDs) are introduced to modify the CsPbI3 surface to improve interface contact and mitigate energy loss. GQD modification can not only effectively passivate surface defects via coordinating with the undercoordinated Pb2+ but also improve energy level alignment, contributing to efficient charge extraction and suppression of nonradiative recombination. Consequently, GQDs-based inverted CsPbI3 devices deliver a champion power conversion efficiency (PCE) of 18.98% with a high open-circuit voltage (VOC) of 1.141 V and are greatly superior to the control device obtaining a poor PCE of 13.29% with a VOC of 0.986 V. Moreover, GQDs can form a protective layer at the perovskite interface to resist external invasion, significantly boosting the device stability. Our findings establish the promising application of GQD modification as a compelling strategy for achieving high performance inorganic photovoltaic devices.

Suppressing interfacial nonradiative recombination by alkali hydroxides for efficient blue perovskite light-emitting diodes

Blue perovskite light-emitting diodes (PeLEDs) provide unlimited possibility in the field of optoelectronic devices due to their excellent characteristics. However, the widely used hole-transport material, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), has strong acidity and poor conductivity which deteriorate the efficiency and stability of perovskite devices. In this work, we modified PEDOT:PSS layer using alkalis, LiOH, NaOH, and KOH, to address these issues. Our findings indicated that the indium defect from indium tin oxide substrate was passivated after the introduction of LiOH, which resulted in the suppression of nonradiative recombination. In addition, the conductivity was improved owing to the increased phase separation of PEDOT:PSS. Taking advantage of optimized interface, the small-n phases of quasi-two-dimensional (quasi-2D) perovskite films were redistributed in quantities and dimensions. As results of these improvements, blue PeLEDs possessed the external quantum efficiencies of 5.95 % and an extended half-lifetime with emission-light wavelength of 473 nm. These findings offer an effective strategy to achieve highly efficient blue light-emitting diode.

Precursor Engineering of Lead Acetate-Based Precursors for High-Open-Circuit Voltage Wide-Bandgap Perovskite Solar Cells.

Wide-bandgap (WBG) perovskites have great potential for inclusion in efficient tandem solar cells, but large open-circuit voltage losses have limited device performance to date. Here, we show that a high-quality WBG perovskite, FA0.83Cs0.17Pb(I0.8Br0.2)3, with enlarged grain sizes and improved crystallinity can be achieved by incorporating lead chloride (PbCl2) into a lead acetate (PbAc2)-based precursor. The improved film quality resulted in the suppression of nonradiative recombination and a reduction in defect density. Efficient WBG perovskite solar cells (1.66 eV) with an efficiency of 19.3% and a high Voc of 1.22 V were fabricated using a facile one-step spin-coating method without the need for an antisolvent. Notably, the unencapsulated devices retained 90% of their initial power conversion efficiency after storage in a dry box (10% humidity) for 800 h.

Suppressing non-radiative recombination in metal halide perovskite solar cells by synergistic effect of ferroelasticity

The low fraction of non-radiative recombination established the foundation of metal halide perovskite solar cells. However, the origin of low non-radiative recombination in metal halide perovskite materials is still not well-understood. Herein, we find that the non-radiative recombination in twinning-tetragonal phase methylammonium lead halide (MAPbIxCl3-x) is apparently suppressed by applying an electric field, which leads to a remarkable increase of the open-circuit voltage from 1.12 V to 1.26 V. Possible effects of ionic migration and light soaking on the open-circuit voltage enhancement are excluded experimentally by control experiments. Microscopic and macroscopic characterizations reveal an excellent correlation between the ferroelastic lattice deformation and the suppression of non-radiative recombination. The calculation result suggests the existence of lattice polarization in self-stabilizable deformed domain walls, indicating the charge separation that facilitated by lattice polarization is accountable for the suppressed non-radiative recombination. This work provides an understanding of the excellent performance of metal halide perovskite solar cells.

Antimony Doping of CsBi3I10 for Tailoring the Film Morphology and Defects toward Efficient Lead-Free Thin-Film Solar Cells

The CsBi3I10 (CBI) semiconductor as a light absorber emerges as a promising alternative to lead-based perovskites owing to its low toxicity, good stability, and satisfying physical properties. However, CBI exhibits an uncontrollable crystallization process, poor film morphology, high defect density, and short carrier lifetime, which lead to inferior optoelectronic properties, limiting its practical application in solar cell devices. Here, the Sb doping strategy is successfully developed for CBI films by a one-step antisolvent-free fabrication method. It is found that Sb incorporation in binary CsBi3–xSbxI10 can modulate the crystallization kinetics and optimize the film quality. As a result, polycrystalline films with high density and few pinholes are obtained to enable the enhancement of light absorbance, reduction of defects, suppression of nonradiative recombination, and increase of surface hydrophobicity. The solar cells based on the CsBi2.7Sb0.3I10 film show a remarkably improved power conversion efficiency of 0.82% compared to that of pristine CBI (0.22%), which is among the highest reported efficiencies for CBI-based thin-film solar cells. Moreover, unencapsulated devices based on Sb-doped CBI exhibit outstanding environmental stability and moisture tolerance. This work not only offers insights into understanding the binary Bi-based materials but also provides a new way to fabricate efficient and stable Bi-based solar cells.

Improving perovskite solar cell performance by compositional engineering via triple-mixed cations

Compositional engineering with the addition of organic and inorganic cations is regarded as an effective way to improve the performance of perovskite solar cells (PSCs). However, exploration of triple-mixed cations in PSCs is still in its initial stage. In this study, triple cations of MA+, FA+, and Gua+ are mixed into perovskite and moulded into a 3D structure by the two-step deposition method, thus proving the feasibility of the triple-cation-based perovskite layer. Through the results of X-ray diffraction (XRD), scanning electron microscope (SEM), and Photoluminescence (PL) tests, Guay(FAMA)1-yPbIxCl3-x perovskite crystallisation was observed. The triple-mixed, cation-based perovskite film exhibits improved crystal quality, larger grain size, and fewer trap densities, all of which are positive for final power conversion efficiency (PCE) and stability. Based on the optimised MA+ and FA+ component ratio, the PSC showed the best performance with a GuaI doping concentration of 10%. The introduction of GuaI further improves the performance of devices by the passivation of defects and suppression of nonradiative recombination. The final PSCs displayed the best PCE (21.3%), as well as enhanced stability.

Suppression of non-radiative recombination with efficient doping of Spiro-OMeTAD for high-performance perovskite solar cells

Metal-halide perovskite solar cells (PSCs) have attracted considerable attention during the past decade. However, due to the existence of non-radiative recombination losses, the best power conversion efficiency (PCE) is still lower than the theoretical limit defined by Shockley-Queser theory. In this work, we investigate 1,2,3-oxathiazin-4(3h)-one, 6-methyl-2,2-dioxide (acesulfame potassium, abbreviated as AK) as a additional dopant for the 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9′-spirobifluorene (Spiro-OMeTAD) and fabricate PSCs in the air. It is found that 12 mol% fraction of AK relative to lithium bis((trifluoromethyl)sulfonyl)-amide (Li-TFSI) reduces the non-radiative recombination from 86.05% to 69.23%, resulting in an average 0.08 V of Voc enhancement. The champion solar cell gives a perovskite solar cells up to 21.9% and over 84% retention of the initial value during 720 h aging in dry air with 20%–30% humidity.

Growth of Amorphous Passivation Layer Using Phenethylammonium Iodide for High‐Performance Inverted Perovskite Solar Cells

Organic–inorganic lead halide perovskite solar cells have realized a rapid increase of power conversion efficiency (PCE) in the past few years. However, their performance still suffers trap‐assisted decline due to defects at the surface and grain boundaries of the perovskite film. Herein, a phenethylammonium iodide‐lead iodide (PEAI‐PbI2) passivation layer is formed on the CH3NH3PbI3 perovskite film. The characterization results indicate that the PEAI covering layer leads to the reduction of surface defects and suppression of nonradiative recombination. By manipulating this surface passivation method, a remarkably improved VOC of 1.16 V and an enhanced PCE of 20.8% are achieved.

Impact of interface recombination on direct-gap photoluminescence from Ge epitaxial layers on Si

Direct-gap photoluminescence (PL) at the wavelength around 1.55 μm from Ge epitaxial layers on Si is studied toward Ge lasers in Si photonics. Comparing the PL intensities under two different wavelengths of excitation lasers, non-radiative interface recombination velocities are estimated to be as large as 105 cm s−1 at Ge/Si and Ge/air interfaces, whereas that at the Ge/GeO2 interface is estimated to be as small as 103–104 cm s−1, which is required for the threshold current density in Ge lasers as low as 10 kA cm−2. In order to remove the effect of defect-rich Ge/Si hetero-interfaces with a high recombination velocity, a wet chemical treatment in a CH3COOH/HNO3/HF/I2 solution is examined. A preferential etching of Ge at Ge/Si interfaces leads to an enhancement of the PL peak intensity by 83 times. A suppression of non-radiative recombination at the Ge/Si interface should contribute to this enhancement, and such a suppression plays a critical role for Ge lasers.

AlxGa1−xN‐Based Quantum Wells Fabricated on Macrosteps Effectively Suppressing Nonradiative Recombination

AbstractAlxGa1−xN‐based quantum wells (QWs) are fabricated on AlN with macrosteps, which are formed by using vicinal sapphire and AlN (0001) substrates. The QWs on macrosteps (MS‐QWs) show photoluminescence lifetimes of nearly 2 ns at an emission wavelength of 242 nm at room temperature (RT). This is the longest lifetime so far reported for AlxGa1−xN‐based QWs emitting below 270 nm, indicating the suppression of nonradiative recombination, the dominant recombination process at RT. Compared with planar QWs without macrosteps, the emission internal quantum efficiency estimated by photoluminescence spectroscopy is improved approximately by two orders of magnitude under a weak excitation condition. Consequently, AlxGa1−xN‐based MS‐QWs are promising structures for highly efficient ultraviolet emitters.

On the Impact of Barrier-Layer Doping on the Photoluminescence Efficiency of InGaAlAs/InGaAs/InP Strained-Layer Heterostructures

The photoluminescence of strained InGaAlAs/InGaAs/InP heterostructures with an active region consisting of nine In0.74Ga0.26As quantum wells and δ-doped In0.53Al0.20Ga0.27As barrier layers grown by molecular beam epitaxy on an InP(100) substrate is investigated. Analysis of the photoluminescence spectra demonstrates that p-type doping leads to an increase in the photoluminescence efficiency at low excitation levels in comparison to a heterostructure with undoped barriers, and increasing the level of barrier doping to (1–2) × 1012 cm–2 results in the suppression of nonradiative recombination.

Влияние легирования барьерных слоев на эффективность фотолюминесценции напряженных гетероструктур InGaAlAs/InGaAs/InP

AbstractThe photoluminescence of strained InGaAlAs/InGaAs/InP heterostructures with an active region consisting of nine In_0.74Ga_0.26As quantum wells and δ-doped In_0.53Al_0.20Ga_0.27As barrier layers grown by molecular beam epitaxy on an InP(100) substrate is investigated. Analysis of the photoluminescence spectra demonstrates that p -type doping leads to an increase in the photoluminescence efficiency at low excitation levels in comparison to a heterostructure with undoped barriers, and increasing the level of barrier doping to (1–2) × 10^12 cm^–2 results in the suppression of nonradiative recombination.

Identifying and suppressing interfacial recombination to achieve high open-circuit voltage in perovskite solar cells

Dopants in the hole transport layer limit the open-circuit voltage of perovskite solar cells.

Enhanced Luminescence Properties of InAs–InAsP Core–Shell Nanowires

Utilizing narrow band gap nanowire (NW) materials to extend nanophotonic applications to the mid-infrared spectral region (>2-3 μm) is highly attractive, however, progress has been seriously hampered due to their poor radiative efficiencies arising from nonradiative surface and Auger recombination. Here, we demonstrate up to ~ 10(2) times enhancements of the emission intensities from InAs NWs by growing an InAsP shell to produce core-shell NWs. By systematically varying the thickness and phosphorus (P)-content of the InAsP shell, we demonstrate the ability to further tune the emission energy via large strain-induced peak shifts that already exceed >100 meV at comparatively low fractional P-contents. Increasing the P-content is found to give rise to additional line width broadening due to asymmetric shell growth generated by a unique transition from {110}- to {112}-sidewall growth as confirmed by cross-sectional scanning transmission electron microscopy. The results also elucidate the detrimental effects of plastic strain relaxation on the emission characteristics, particularly in core-shell structures with very high P-content and shell thickness. Overall, our findings highlight that enhanced mid-infrared emission efficiencies with effective carrier confinement and suppression of nonradiative recombination are highly sensitive to the quality of the InAs-InAsP core-shell interface.

Improved photovoltaic performance of crystalline-Si/organic Schottky junction solar cells using ferroelectric polymers

The effect of inserting an ultrathin layer of ferroelectric (FE) poly(vinylidene fluoride-tetrafluoroethylene) P(VDF-TeFE) at the crystalline (c-)Si/poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) interface of a c-Si/PEDOT:PSS Schottky junction solar cell is demonstrated. P(VDF-TeFE) is a highly resistive material that exhibits a large, permanent, internal polarization electric field by poling of molecular dipole among the polymer chains. Because of these properties, performance can be enhanced by adjusting the thickness of the FE layer and subsequent poling process. Inserting a 3-nm-thick FE layer increases the power conversion efficiency η from 10.2% to 11.4% with a short-circuit current density Jsc of 28.85 mA/cm2, an open-circuit voltage Voc of 0.57 V, and a fill factor FF of 0.692. Subsequent poling of the FE layer under a reverse DC bias stress increased η up to 12.3% with a Jsc of 29.7 mA/cm2, a Voc of 0.58 V, and an FF of 0.71. The obtained results confirm that the spontaneous polarization of the FE layers is responsible for the enhancement of η, and that the polarization-based enhancement works if the FE layer is highly crystalline. These findings originate from efficient charge extraction to the electrodes and a suppression of non-radiative recombination at the c-Si/PEDOT:PSS interface.

Suppression of nonradiative recombination in ionic insulators by defects: Role of fast electron trapping in Tl-doped CsI

In semiconductors, defects often assist nonradiative relaxation. However, Tl doping can significantly suppress the nonradiative relaxation in alkali halides to increase scintillation efficiency. Without the Tl, it is known that the creation of Frenkel pairs at self-trapped excitons, assisted by excited electron and hole relaxations, is the reason for the nonradiative relaxation. Here we show by first-principles calculation that Tl doping introduces Tl $p$ states inside the band gap to trap the excited electrons. The trapping is highly effective to within several picoseconds, as revealed by time-dependent density functional theory calculations. It alters the nonradiative relaxation process to result in a noticeable increase in the relaxation barrier from 0.3 to 0.63 eV, which reduces the nonradiative relaxation by roughly a factor of 10${}^{5}$ at room temperature.

Synthesis and Luminescent Behavior of Mn<sub>(1-X)</sub>S:A<sub>X</sub>/ZnS Core/Shell Nanocrystals

Mn(1-X)S:AX/ZnS (A: Er, Dy) nanocrystals were synthesized by chemical precipitation method. X-ray diffraction analysis show that Mn(1-X)S:AX/ZnS nanocrystals were zincblende structure. The high-resolution transmission electron microscope images indicated that Mn(1-X)S:AX/ZnS nanocrystals show a spherical shape, and their average grain size is about 4 nm. Photoluminescence spectra of Mn(1-X)S:AX/ZnS nanocrystals revealed that there existed several major emission bands, ～417 nm, ~509 nm, ~580 nm, ~617nm and ~680 nm. Mn(1-X)S:AX/ZnS nanocrystals exhibited enhanced luminescence properties compared with the pure Mn(1-X)S:AX nanocrystals. The enhanced photoluminescence properties of Mn(1-X)S:AX/ZnS nanocrystals should be attributed to the effective suppression of nonradiative recombination by the surface-passivation layer.