Passivation Of Surface Defects Research Articles

2D/3D heterojunction engineering for hole transport layer-free carbon-based perovskite solar cells.

Hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) own outstanding potential for commercial applications due to their attractive advantages of low cost and superior stability. However, the abundant defects and mismatched energy levels at the interface of the perovskite/carbon electrode severely limit the device efficiency and stability. Constructing a 2D layer on the surface of 3D perovskite films to form 2D/3D heterojunctions has been demonstrated to be an effective method of passivating surface defects and optimizing the energy level alignment in almost all kinds of PSCs. Due to the unique structure of HTL-free C-PSCs, 2D/3D heterojunctions play especially important roles. This review article summarizes the reports of 2D/3D perovskite heterojunctions in HTL-free C-PSCs. It describes the contributions of 2D/3D heterojunctions in terms of their roles in defect passivation, energy level optimization, and stability improvement. Finally, challenges and prospects of 2D/3D heterojunction for further development of HTL-free C-PSCs are highlighted.

Comprehensive Passivation of Surface and Bulk Defects in Perovskite for High Efficiency Carbon-Based CsPbI3 Solar Cells.

Carbon-based perovskite solar cells (C-PSCs) have the advantages of high stability and low cost, but their mean efficiency has become an obstacle to commercialization. Defects, which are widely distributed on the surface and bulk of films, are an important factor in C-PSCs for low efficiency. The conventional post-treatment method through forming a low-dimensional (LD) perovskite layer usually fails in manipulating the bulk defects. Herein, we propose a strategy of combining wet film (uncrystallized) treatment with dry film treatment to in situ form LD perovskite throughout the grain boundaries inside of the film and on the surface of the film, thereby simultaneously passivating the bulk and surface defects in the CsPbI3 film. As a result, the photoluminescence lifetime is significantly improved from 22.5 ns to 92.1 ns. The assembled CsPbI3 C-PSCs based on the above strategy deliver a champion efficiency of 19.65%, which is a new record efficiency for inorganic C-PSCs.

Comprehensive Passivation of Surface and Bulk Defects in Perovskite for High Efficiency Carbon‐Based CsPbI3 Solar Cells

Carbon‐based perovskite solar cells (C‐PSCs) have the advantages of high stability and low cost, but their mean efficiency has become an obstacle to commercialization. Defects, which are widely distributed on the surface and bulk of films, are an important factor in C‐PSCs for low efficiency. The conventional post‐treatment method through forming a low‐dimensional (LD) perovskite layer usually fails in manipulating the bulk defects. Herein, we propose a strategy of combining wet film (uncrystallized) treatment with dry film treatment to in situ form LD perovskite throughout the grain boundaries inside of the film and on the surface of the film, thereby simultaneously passivating the bulk and surface defects in the CsPbI3 film. As a result, the photoluminescence lifetime is significantly improved from 22.5 ns to 92.1 ns. The assembled CsPbI3 C‐PSCs based on the above strategy deliver a champion efficiency of 19.65%, which is a new record efficiency for inorganic C‐PSCs.

Simultaneous passivation of surface and bulk defects in all‐perovskite tandem solar cells using bifunctional lithium salts

AbstractAll‐perovskite tandem solar cells have garnered considerable attention because of their potential to outperform single‐junction cells. However, charge recombination losses within narrow‐bandgap (NBG) perovskite subcells hamper the advancement of this technology. Herein, we introduce a lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), for modifying NBG perovskites. Interestingly, LiTFSI bifunctionally passivates the surface and bulk of NBG by dissociating into Li+ and TFSI− ions. We found that TFSI− passivates halide vacancies on the perovskite surface, reducing nonradiative recombination, while Li+ acts as an interstitial n‐type dopant, mitigating the defects of NBG perovskites and potentially suppressing halide migration. Furthermore, the underlying mechanism of LiTFSI passivation was investigated through the density functional theory calculations. Accordingly, LiTFSI facilitates charge extraction and extends the charge carrier lifetime, resulting in an NBG device with power conversion efficiency (PCE) of 22.04% (certified PCE of 21.42%) and an exceptional fill factor of 81.92%. This enables the fabrication of all‐perovskite tandem solar cells with PCEs of 27.47% and 26.27% for aperture areas of 0.0935 and 1.02 cm2, respectively.image

DMSO-Assisted Control Enables Highly Efficient 2D/3D Hybrid Perovskite Solar Cells.

Building 2D/3D heterojunction is a promising approach to passivate surface defects and improve the stability of perovskite solar cells (PSCs). Developing effective methods to build high-quality 2D/3D heterojunction is in demand. The formation of 2D/3D heterojunction involves both the diffusion of 2D spacer molecules and phase transition from 3D to 2D structure. Herein, a DMSO-assisted method is demonstrated to simultaneously regulate both the 2D/3D formation kinetics, yielding high-quality 2D top layer with continuous coverage, which enhances the photovoltaic performance of PSCs. It is found that the presence of DMSO significantly facilitates the diffusion of 2D spacer cation. Meanwhile the residual DMSO may partially dissolve the surface perovskite, facilitating the reaction between 2D molecules with 3D perovskite and ultimately leading to sequential secondary crystal growth and the appearance of a distinct 2D layer. The formation of high-quality 2D layer effectively passivates the surface defects thus suppresses the interfacial charge recombination. As a result, the champion PSC based on optimal 2D/3D heterojunction exhibits a high fill factor of 85% and a power conversion efficiency of 24%. The work offers a novel perspective for the construction of 2D/3D perovskite heterojunctions.

Effects of Polymer Matrix and Atmospheric Conditions on Photophysical Properties of a Cesium Lead Bromide (CsPbBr3) Perovskite Quantum Dot.

Understanding the environment-dependent stability and photoluminescence (PL) properties of advanced perovskite materials remains a challenge with conflicting views. Herein, we investigated the influence of the host matrix (poly(methyl methacrylate) (PMMA) and polystyrene (PS)) and atmospheric conditions (ambient and N2) on the PL properties of a CsPbBr3 perovskite quantum dot (PQD) using single-particle spectroscopy. Despite the same PL blinking mechanism, the PL properties of the PQD were considerably affected by the environmental conditions. The charge trapping and detrapping rates of the PQD were lower and higher, respectively, under ambient atmosphere than under N2 owing to surface defect passivation by oxygen. The frequency and rate of PQD decomposition were higher in the PMMA matrix than in the PS matrix under an ambient atmosphere. PS achieved superior PQD encapsulation owing to its higher affinity toward hydrophobic surface ligands because of its aromatic rings, thereby protecting the PQD surface from moisture and thus inhibiting decomposition.

Self-Assembled Monolayer-Functionalized NiO Hole Injection layer for Improved Charge Injection in Quantum Dot Light-Emitting Diodes.

The development of quantum dot light-emitting diodes (QLEDs) represents a promising advancement in next-generation display technology. However, there are challenges, especially in achieving efficient hole injection, maintaining charge balance, and replacing low-stability organic materials such as PEDOT:PSS. To address these issues, in this study, self-assembled monolayers (SAMs) were employed to modify the surface properties of NiO, a hole injection material, within the structure of ITO/HIL/TFB/QDs/ZnMgO/Al QLEDs. Specifically, using Br-2PACz-based SAMs resulted in surface defect passivation, improved hole injection, reduced exciton quenching, and enhanced electrical characteristics. Notably, QLEDs based on (NiO+Br-2PACz) demonstrated a turn-on voltage of 2.4 V, a maximum external quantum efficiency (EQE) of 8.30%, a maximum luminance of 88,831 cd/m2, and a maximum current efficiency of 32.78 cd/A. Compared to NiO-based QLEDs, these results represent a reduction in turn-on voltage by approximately 1.5 V, a 1.99-fold increase in EQE, and a 3.63-fold increase in luminance, indicating significantly enhanced performance with notable improvements in turn-on voltage, EQE, and luminance. They also showed higher EQE and luminance than PEDOT:PSS-based QLEDs; this could be attributed to the downshifting of energy levels by Br-2PACz, which reduced the hole injection barrier, increased the conductivity, and improved charge balance. In particular, the reduction in exciton quenching and the increase in electrical conductivity contributed significantly to the overall performance enhancement of the (NiO+Br-2PACz)-based QLEDs. This paper proposes a simple method for inorganic hole injection layer functionalize and application.

Study of Thermalization Mechanisms of Hot Carriers in BABr-Added MAPbBr3 for the Top Layer of Four-Junction Solar Cells.

The hot carrier multi-junction solar cell (HCMJC) is an advanced-concept solar cell with a theoretical efficiency greater than 65%. It combines the advantages of hot carrier solar cells and multi-junction solar cells with higher power conversion efficiency (PCE). The thermalization coefficient (Qth) has been shown to slow down by an order of magnitude in low-dimensional structures, which will significantly improve PCE. However, there have been no studies calculating the Qth of MAPbBr3 quantum dots so far. In this work, the Qth values of MAPbBr3 quantum dots and after BABr addition were calculated based on power-dependent steady-state photoluminescence (PD-SSPL). Their peak positions in PD-SSPL increased from 2.37 to 2.71 eV after adding BABr. The fitting shows that, after adding BABr, the Qth decreased from 2.64 ± 0.29 mW·K-1·cm-2 to 2.36 ± 0.25 mW·K-1·cm-2, indicating a lower relaxation rate. This is because BABr passivates surface defects, slowing down the carrier thermalization process. This work lays the foundation for the theoretical framework combining perovskite materials, which suggests that the appropriate passivation of BABr has the potential to further reduce Qth and make MAPbBr3 QDs with BABr modified more suitable as the top absorption layer of HCMJCs.

Enhanced Performance and Stability of CsPbBr3 Perovskite Solar Cells Using Trioctylphosphine Oxide Additive.

This study investigates the application of trioctylphosphine oxide (TOPO) and triphenylphosphine oxide (TPPO) as an additive to enhance the performance of all-inorganic CsPbBr3 perovskite solar cells (PSCs). The addition of TOPO and TPPO passivates surface defects, increases grain size, and reduces surface trap states, leading to better light absorption and accelerated carrier transport. These modifications lead to an optimized energy level distribution, resulting in a significant increase in power conversion efficiency from 5.14 to 9.21% with TOPO and from 5.14% to 7.28% with TPPO. Furthermore, the long alkyl chains in TOPO provide effective isolation from air and water, significantly enhancing device stability for over 2400 h without packaging. The findings demonstrate that oxygen phosphine additives with long alkane chains are more effective in improving PSCs than those with aromatic hydrocarbons, offering new insights for the use of passivators in perovskite solar cells.

Synergistic Modulation of Orientation and Steric Hindrance Induced by Alkyl Chain Length in Ammonium Salt Passivator Toward High-performance Inverted Perovskite Solar Cells and Modules.

Organic ammonium salts are extensively utilized for passivating surface defects in perovskite films to mitigate trap-assisted nonradiative recombination. However, the influence of alkyl chain length on the molecular orientation and spatial steric hindrance of ammonium salt remains underexplored, hindering advancements in more effective passivators. Here, a series of organic ammonium salts is reported with varying alkyl chain lengths to passivate surface defects and optimize band alignment. It is revealed that long alkyl chains promote parallel molecular orientation on the perovskite surface, thereby reinforcing interaction with surface defects, whereas excessive chain length introduces steric hindrance, weakening anion-perovskite interactions. Nonylammonium acetate (NAAc) with optimal chain length achieves the ideal balance between chemical interactions, resulting in superior passivation. Through NAAc passivation, high-performance inverted perovskite solar cells (PSCs) and modules are achieved, with power conversion efficiencies (PCE) of 25.79% (certified 25.12%) and 19.62%, respectively. This marks a record PCE for inverted PSCs utilizing vacuum flash technology in ambient conditions. Additionally, the NAAc-passivated devices retain 91% of their initial PCE after 1200h of continuous maximum power point operation. This work offers new insights into the interplay between molecular orientation and steric hindrance, advancing the design of high-performance PSCs.

Enhancing the Efficiency and Stability of Inverted Perovskite Solar Cells and Modules through Top Interface Modification with N‐type Semiconductors

The interface modification between perovskite and electron transport layer (ETL) plays a crucial role in achieving high performance inverted perovskite photovoltaics (i‐PPVs). Herein, non‐fullerene acceptors (NFAs), known as Y6‐BO and Y7‐BO, were utilized to modify the perovskite/ETL interface in i‐PPVs. Non‐polar solvent‐soluble NFAs can effectively passivate surface defects without structural damage of the underlying perovskite films. Additionally, the improved PCBM ETL induced by NFAs modification significantly accelerates the electrons extraction. As a result, both Y6‐BO and Y7‐BO exhibit more effective interface modification effects compared to traditional PI molecules. The power conversion efficiency (PCE) of the inverted perovskite solar cell (i‐PSC) modified with Y7‐BO reaches 25.82%. Moreover, the adoption of non‐polar solvents and the superior semiconductor properties of Y7‐BO molecules also enable perovskite solar modules (i‐PSM) with effective areas of 50 cm2, 400 cm2, and 1160 cm2 to achieve record efficiencies of 23.05%, 22.32%, and 21.1% (certified PCE), respectively, making them the best PCE reported in the literature. Importantly, enhanced interface mechanical strength between the perovskite and PCBM layer results in significantly improved environmental and operational stability of the cells. The cells modified with Y7‐BO maintained 94.4% of the initial efficiency after 1522 hours of maximum power point aging.

Enhancing the Efficiency and Stability of Inverted Perovskite Solar Cells and Modules through Top Interface Modification with N-type Semiconductors.

The interface modification between perovskite and electron transport layer (ETL) plays a crucial role in achieving high performance inverted perovskite photovoltaics (i-PPVs). Herein, non-fullerene acceptors (NFAs), known as Y6-BO and Y7-BO, were utilized to modify the perovskite/ETL interface in i-PPVs. Non-polar solvent-soluble NFAs can effectively passivate surface defects without structural damage of the underlying perovskite films. Additionally, the improved phenyl-C61-butyric acid methyl ester (PCBM) ETL induced by NFAs modification significantly accelerates the electrons extraction. As a result, both Y6-BO and Y7-BO exhibit more effective interface modification effects compared to traditional PI molecules. The power conversion efficiency (PCE) of the inverted perovskite solar cell (i-PSC) modified with Y7-BO reaches 25.82 %. Moreover, the adoption of non-polar solvents and the superior semiconductor properties of Y7-BO molecules also enable perovskite solar modules (i-PSM) with effective areas of 50 cm2, 400 cm2, and 1160 cm2 to achieve record efficiencies of 23.05 %, 22.32 %, and 21.1 % (certified PCE), respectively, making them the best PCE reported in the literature. Importantly, enhanced interface mechanical strength between the perovskite and PCBM layer results in significantly improved environmental and operational stability of the cells. The cells modified with Y7-BO maintained 94.4 % of the initial efficiency after 1522 hours of maximum power point aging.

2,2′‐Bipyridyl‐4,4′‐Dicarboxylic Acid Modified Buried Interface of High‐Performance Perovskite Solar Cells

AbstractThe regulation of interfaces remains a critical and challenging aspect in the pursuit of highly efficient and stable perovskite solar cells (PSCs). Here, 2,2′‐bipyridyl‐4,4′‐dicarboxylic acid (HBPDC) is incorporated as an interfacial layer between SnO2 and perovskite layers in PSCs. The two carboxylic acid moieties on HBPDC bind to SnO2 through esterification, while its nitrogen atoms, possessing lone electron pairs, interact with uncoordinated lead (Pb2+) atoms through Lewis acid‐base interactions. This dual functionality enables simultaneous passivation of surface defects on both the SnO2 and buried perovskite layers. In addition, the electron‐deficient nature of HBPDC enhances interfacial energy band alignment and facilitates electron transfer from the perovskite to SnO2. Furthermore, the incorporation of HBPDC strengthens the interfacial adhesion, improving mechanical reliability. As a result, the PSCs exhibited an impressive power conversion efficiency (PCE) of 25.41 % under standard AM 1.5G conditions, along with remarkable environmental stability.

Surface n-Doped Metal Halide Perovskite for Efficient and Stable Solar Cells through Organic Chelation.

Perovskite solar cells (PSCs) have emerged as a leading photovoltaic technology due to their high efficiency and low cost. Even though they have developed rapidly since their inception, with efficiencies of over 26%, inverted PSCs face challenges such as nonradiative recombination and ion migration. Surface treatment, especially the utilization of organic compounds, has improved efficiency and stability by optimizing the perovskite-charge transport layer interface. Herein, we report a facile and effective strategy by introducing 2,2'-bipyridyl to modify the surface of perovskite, achieving a power conversion efficiency of 24.43% with increasing open-circuit voltage and fill factor and good repeatability on multiple devices. We reveal that the 2,2'-bipyridyl molecule can chelate lead ions on the surface of perovskite, effectively suppressing nonradiative recombination. Furthermore, this modification can induce surficial n-doping to refine the energy level alignment, thereby minimizing charge transport losses. Additionally, the device maintained over 92% of the initial efficiency after 1000 h of operation at the maximum power point under continuous illumination. This surface chelation and defect passivation strategy employing 2,2'-bipyridyl offers a promising avenue for exploring the details of potential long-term degradation mechanisms and the development of commercially viable high-performance p-i-n PSCs.

Low-dimensional phase optimization and defect passivation of quasi-2D perovskite to enhance electroluminescence by introducing b-NA

The energy funnel effect holds significant potential for enhancing light-emitting diodes (LEDs) performance in the Quasi-two-dimensional (Quasi-2D) perovskite, which feature a unique multi-quantum well structure. However, random phase distribution and defects within Quasi-2D films pose challenges, leading to inefficient energy transfer and nonradiative recombination, thereby limiting device performance. Here, sodium 2-naphthalene sulfonate (b-NA) is introduced into the Quasi-2D perovskite film to enhance its the optical and electrical properties. The strong interaction between the S = O group and Na+ in b-NA with the perovskite matrix leads to reduced grain size, facilitating agglomeration and densification. This modification decreases the proportion of the low-n phase, enhances thermal stability, and passivates surface defects. Therefore, compared to the control device, the maximum brightness and external quantum efficiency of Quasi-2D perovskite LEDs with the optimal concentration (8b-NA) more than double, and the operational lifetime (T50) of the unpackaged device extends from 70.1 min to 168.5 min.

Selective passivation of 2D MoS2 nanosheets surface defects by spontaneous growth of Au nanoparticles for full response-recovery NO2 detection at room temperature

Full recovery at room temperature (RT) is quite challengng for two dimensional transition metal dichalcogenides chemiresistive gas sensors. The main reason for the incomplete recovery is the strong bonding of gas molecules onto sensing layer defects. Here, we show that the recovery rate of MoS2 chemiresistive NO2 sensors can be improved by selective passivation of MoS2 nanosheets (NSs) defects with Au nanoparticles (NPs) via a simple spontaneous reduction method. MoS2 NSs were produced by liquid shear exfoliation. Pristine and Au NPs functionalized MoS2 were characterized using ς-potential, UV–Visible spectroscopy, TEM, SEM, AFM, EDS, XRD, XPS and Raman spectroscopy. The analyses confirm the presence of Au NPs on the edges of MoS2 NSs at defective sites with NP sizes of 1–4 nm and 5–30 nm. Both pristine MoS2 and Au-decorated MoS2 NSs were employed to fabricate NO2 chemiresistive devices. Au-decorated MoS2 sensors showed an improved performance (for 1 ppm NO2, Au-MoS2 sensor exhibited a response of 5.6 % instead of 2.2 % for MoS2 sensor), and gave faster response and better recovery time. Concurrently, the functionalization is independent of the adsorption and desorption of NO2. Most importantly, the functionalization of MoS2 NSs helps to full response-recovery within one hour, without either thermal or UV irradiation treatment.

Oxygen plasma treatment to passivate surface defects for high stability CsPbCl2Br light emitting diodes

Metal halide perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for blue light emission by mixing halides such as bromine (Br) and chlorine (Cl). However, these mixed halide perovskites often suffer from halogen separation under light illumination, leading to spectral shifts and performance degradation. Reducing surface defects in perovskites is critical to preventing ion migration, enhancing film stability, and preventing photo-induced phase separation. In this study, we develop an oxygen plasma treatment strategy to create new perovskite surfaces with lower trap densities by optimizing the plasma power and treatment duration. This treatment dissociates oxygen into ions that form strong Pb–O bonds with uncoordinated lead ions on the perovskite surface, effectively passivating surface defects and prevent ion migration. As a result, the photoluminescence intensity of the CsPbCl2Br film is significantly improved, with no halogen separation observed even after 12 h of continuous 25 W/cm2 laser illumination. Use the optimized thin film, we fabricated all-inorganic Ag/N–Si/CsPbCl2Br/NiO/ITO LEDs that achieved deep blue light emission with high color purity at a 443 nm (full width at half maxima of 18 nm). Notably, these PeLEDs exhibite excellent spectral stability, with only a slight EL peak shift even at a high operational voltage of 7 V. The oxygen plasma treatment demonstrated in this study provides a promising method for reducing surface defects and suppressing phase separation in mixed halides, offering significant potential for developing highly stable deep blue perovskite LED applications.

Efficient Energy Transfer from Quantum Dots to Closely‐Bound Dye Molecules without Spectral Overlap

Quantum dots (QDs) are semiconductor nanocrystals whose optical properties can be tuned by altering their size. By combining QDs with dyes we can make hybrid QD‐dye systems exhibiting energy transfer (ET) between QDs and dyes, which is important in sensing and lighting applications. In conventional QDs that need a shell to passivate surface defects, ET usually proceeds through Förster resonance energy transfer (FRET) that requires significant spectral overlap between QD emission and dye absorbance, as well as large oscillator strengths of those transitions. This considerably limits the choice of dyes. In contrast, perovskite QDs do not require passivating shells for bright emission, which makes ET mechanisms beyond FRET accessible. This work explores the design of a CsPbBr3 QD‐dye system to achieve efficient ET from CsPbBr3 QDs to dyes with dimethyl iminium binding groups where the close binding of dyes surface facilitates spatial wavefunction overlap. Using steady‐state and time‐resolved photoluminescence experiments, we demonstrate that efficient ET from CsPbBr3 to dyes with minimal spectral overlap proceeds via the Dexter exchange‐type mechanism, which overcomes the conventional restriction of spectral overlap that severely limits the tunability of these systems. This approach opens new avenues for QD‐molecule hybrids for a wide range of applications.

Efficient Energy Transfer from Quantum Dots to Closely-Bound Dye Molecules without Spectral Overlap.

Quantum dots (QDs) are semiconductor nanocrystals whose optical properties can be tuned by altering their size. By combining QDs with dyes we can make hybrid QD-dye systems exhibiting energy transfer (ET) between QDs and dyes, which is important in sensing and lighting applications. In conventional QDs that need a shell to passivate surface defects, ET usually proceeds through Förster resonance energy transfer (FRET) that requires significant spectral overlap between QD emission and dye absorbance, as well as large oscillator strengths of those transitions. This considerably limits the choice of dyes. In contrast, perovskite QDs do not require passivating shells for bright emission, which makes ET mechanisms beyond FRET accessible. This work explores the design of a CsPbBr3 QD-dye system to achieve efficient ET from CsPbBr3 QDs to dyes with dimethyl iminium binding groups where the close binding of dyes to CsPbBr3 surface facilitates spatial wavefunction overlap. Using steady-state and time-resolved photoluminescence experiments, we demonstrate that efficient ET from CsPbBr3 to dyes with minimal spectral overlap proceeds via the Dexter exchange-type mechanism, which overcomes the conventional restriction of spectral overlap that severely limits the tunability of these systems. This approach opens new avenues for QD-molecule hybrids for a wide range of applications, such as lighting.

Formation and Passivation of Surface Defects in Lead-Free Tin Halide Perovskites

Formation and Passivation of Surface Defects in Lead-Free Tin Halide Perovskites