Buried Interface Research Articles

Improving Buried Interface Contact for Inverted Perovskite Solar Cells via Dual Modification Strategy

AbstractThe non‐wetting issue of the self‐assembled monolayer (SAM) layer can complicate subsequent perovskite deposition and impact device efficiency. This study addresses this challenge using a dual approach involving co‐self‐assembly and a buffer layer to enhance the wettability and interfacial contact of the buried perovskite film. A weakly acidic boronic acid derivative, 4‐N, N‐dimethylbenzeneboronic acid hydrochloride (4NPBA), is used to co‐self‐assemble with the regular SAM molecule on ITO and the subsequent FAI buffer layer further increased perovskite film coverage to 89%. This dual buried interface strategy—SAM‐4NPBA/FAI—results in a flat and dense perovskite interface. The optimized device demonstrates a high fill factor of 88.35%, a power conversion efficiency of 25.29%, and retains over 99% of its initial efficiency after 500 h of maximum power point testing.

Iodide Management and Oriented Crystallization Modulation for High-Performance All-Air Processed Perovskite Solar Cells.

Halide-related defects at the buried interface not only cause nonradiative recombination, but also seriously impair the long-term stability of perovskite solar cells (PSCs). Herein, a bottom-up, all-in-one modification strategy is proposed by introducing a multisite antioxidant ergothioneine (EGT) at the buried interface to manage iodide ions and manipulate crystallization dynamics. The findings demonstrate that EGT not only passivates uncoordinated Sn4+/Pb2+ defects, but also firmly anchors iodide ions and inhibits their oxidation to I2. Additionally, the modification by EGT enhances the oriented crystallization of perovskite, improves the carrier dynamics, and releases residual stresses. Consequently, the optimized all-air processed device (Rb0.02(FA0.95Cs0.05)0.98PbI2.91Br0.03Cl0.06) achieves a remarkable power conversion efficiency (PCE) of 25.13%, which is among the highest values reported for devices fabricated in air, along with ultrahigh open-circuit voltage (VOC) of 1.191V and fill factor (FF) of 84.9%. The optimized device without encapsulation exhibits strong humidity, thermal, and operational stability under ISOS protocol. Specifically, the initial efficiency of the device is retained at 90.12% after 1512 h of thermal ageing at 65°C and 90.14% after 930 h of continuous maximum power point tracking (MPPT) under simulated AM1.5 illumination.

Tailored Polymer Hole-Transporting Materials with Multisite Passivation Functions for Effective Buried-Interface Engineering of Inverted Quasi-2D Perovskite Solar Cells.

Although quasi-2D Ruddlesden‒Popper (RP) perovskite exhibits advantages in stability, their photovoltaic performance are still inferior to 3D counterparts. Optimizing the buried interface of RP perovskite and suppress energetic losses can be a promising approach for enhancing efficiency and stability of inverted quasi-2D RP perovskite solar cells (PSCs). Among which, constructing polymer hole-transporting materials (HTMs) with defect passivation functions is of great significance for buried-interface engineering of inverted quasi-2D RP PSCs. Herein, by employing side-chain tailoring strategy to extend the π-conjugation and regulate functionality of side-chain groups, target polymer HTMs (PVCz-ThSMeTPA and PVCz-ThOMeTPA) with high mobility and multisite passivation functions are achieved. The presence of more sulfur atom-containing groups in side-chain endows PVCz-ThSMeTPA with increased intra/intermolecular interaction, appropriate energy level, and enhanced buried interfacial interactions with quasi-2D RP perovskite. The hole mobility of PVCz-ThSMeTPA is up to 9.20×10-4 cm2 V-1 S-1. Furthermore, PVCz-ThSMeTPA as multifunctional polymer HTM with multiple chemical anchor sites for buried-interface engineering of quasi-2D PSCs can enable effective charge extraction, defects passivation, and perovskite crystallization modulation. Eventually, the PVCz-ThSMeTPA-based inverted quasi-2D PSC achieves a champion power conversion efficiency of 22.37%, which represents one of the highest power conversion efficiencies reported to date for quasi-2D RP PSCs.

Modifying the buried interface by a sulfamate enable efficient perovskite solar cells with high stability

The buried interface between the pivotal perovskite layer and the electron transfer layer (ETL) greatly affects the photoelectric property of perovskite layer and the final performance of a perovskite solar cell (PSC). Effectively modifying the buried interface is feasible to improve the photoelectric conversion efficiency (PCE) and stability of PSCs. Herein, we employ a sulfamate sodium 4-aminoazobenzene-4′-sulfonate (SABS) with zwitterion to modify the SnO2 film surface to improve the performance of PSCs. The post-treatment makes the surface of SnO2 film smoother and also passivate the anion and cation vacancies of SnO2, which are benefit to the growth of perovskite crystals and strengthen the interface contact between SnO2 layer and perovskite layer. Furthermore, SABS molecules can passivate defects of perovskite layer at the buried interface. By using this post-treating method, the PCE of the final PSC is increased from 21.76 % to 23.86 %, and the storage and operational stability are also significantly improved. This promotion the buried interface via post-treating the SnO2 film with a zwitterion passivator provides a convenient strategy to effectively improve the performance and stability of PSCs.

Influence of an ultrathin Mn ‘spy layer’ on the static and dynamic magnetic coupling within FePt/NiFe bilayers

Abstract We explore whether insertion of an ultrathin Mn ‘spy layer’ within a magnetic hard/soft bilayer can enable depth-sensitive element-specific measurements of the static and dynamic magnetization, while avoiding significant disruption of the original magnetic state. MgO(110)/FePt(100 Å)/NiFe(200 Å)/Mn(tMn Å)/NiFe(200 Å) samples with Mn thicknesses of tMn=0, 5, and 10Å were fabricated by magnetron sputtering and studied by element-selective x-ray magnetic circular dichroism (XMCD), vector network analyzer ferromagnetic resonance (VNA-FMR), and x-ray detected ferromagnetic resonance (XFMR). For tMn= 5 Å, the magnetic reversal properties remain broadly similar to tMn= 0 Å. For tMn=10 Å, the two NiFe layers decouple with XMCD hysteresis loops at the Mn edge showing two switching events that suggest the presence of two distinct Mn-containing regions. While the Mn moments within each region have ferromagnetic order, their relative alignment is antiparallel at high field. Analysis of the magnetic data and additional scanning transmission electron microscopy (STEM) measurements point to the presence of a Mn layer at the lower NiFe/Mn interface, and the formation of a NiFeMn alloy at the upper Mn/NiFe interface. The Mn moments of the former region lie antiparallel to those of the underlying NiFe layer. The VNA-FMR data suggests that for tMn= 5 and 10 Å, the interfacial exchange coupling at the FePt/NiFe is suppressed and the in-plane uniaxial magnetic anisotropy of the NiFe is increased, perhaps due to migration of Mn towards the buried interface. The above findings show that Mn is a problematic magnetic spy, and that a Mn thickness of less than 5Å would be required.

Implementing Lattice and Energy Level Matching to Optimize Buried Interfaces for High-Performance Perovskite Solar Cells.

In n-i-p type perovskite solar cells (PSCs), mismatches in energy level and lattice at the buried interface is highly detrimental to device performance. Here, thin PbS interconnect layer in situ coating on the SnO2 surface is grown. The function of PbS at the interface is different from the commonly used function of crystalline seeds in perovskite bulk. The theoretical calculation show that it helps construct an interconnect structure of SnO2/PbS/Perovskite with matched energy level and lattice. This not only increases conductivity of SnO2, but also upshifts Fermi energy levels (EF) of both SnO2 and buried perovskite due to charge transfer and perovskite's internal defect changes. Such a suitable energy level arrangement ensures a better energy level match at the interface, favoring efficient charge transfer and less open circuit voltage (Voc) loss. Additionally, in situ PL reveals that the template effect of PbS enable perovskite grain to grow bottom-up because of their highly matched lattice parameters. This growth mode optimizes buried interface contact and crystallinity of perovskite. Ultimately, after PbS modification, a remarkable power conversion efficiency (PCE) exceeding 24% and better device stability are obtained. This work demonstrates an effective interconnect layers strategy to realize ideal interface contact toward high-performance PSCs.

Multidentate Polymer-Stabilized Buried Interface for Efficient Planar Perovskite Solar Cells.

Buried interface engineering is crucial to improve the performance and stability of perovskite solar cells (PSCs). Although coordination materials have been widely used for buried interface modification, they are generally engineered on one surface of the interface through monodentate or bidentate molecules. Here, we propose that a multidentate polymer, sodium alginate (SA), acts with both surfaces via numerous C═O groups to reinforce buried interfaces. SA effectively reduces buried interface defects, adjusts the energy level alignment, and refines carrier dynamics. Notably, it also induces the growth of a perovskite film that is less tensile stressed and free of voids. Consequently, the champion device efficiency after SA treatment increased from 23.05% to 24.98%, along with significant improvements in both light and thermal stability. This work offers insights into efficiency and stability improvement from the perspective of multidentate polymer anchoring.

Generation and Clearance of Superoxide Radicals at Buried Interfaces of Perovskites with Different Crystal Structures.

One of the most notorious issues with classic perovskite (MAPbI3) is its rapid degradation caused by generating superoxide radicals (O2 •-) on its surface under light and oxygen environments (light/O2). The differences in O2 •- generation rate and tolerance to O2 •- among perovskite with different structures are pending. For the first time it is validated through solid-electron paramagnetic resonance (EPR) that MAPbI3 and Cs0.175FA0.75MA0.075PbI3 (PVSK) crystals can generate O2 •- in an air atmosphere. The rapid degradation of perovskite buried interfaces caused by O2 •- dominates the nonexposed air aging process of SnO2-based perovskite film, and the degradation rate of MAPbI3 film is faster than that of PVSK film. The fullerene pyridine derivatives (C60OPD), which function as a buffer layer between SnO2 and PVSK to scavenge O2 •- and prevent degradation at the buried interface of the PVSK film, reduce the density of defect states, and accelerate the transmission of photogenerated electrons. The photoelectric conversion efficiency (PCE) of perovskite solar cells (PSCs) optimizes with C60OPD increased from 21.15% to 23.11% while significantly improving the stability in light/O2. This work reveals the hidden degradation of perovskite-buried interfaces caused by O2 •- and explores efficient ways for perovskite to resist O2 •-.

Efficient and Stable Perovskite Solar Cells and Modules Enabled by Tailoring Additive Distribution According to the Film Growth Dynamics

HighlightsTwo pre-crystallization processes of gas quenching and vacuum quenching lead to different order of crystallization dynamics within the perovskite thin film, resulting in the differences of additive distribution.A tailor designed 1,3-bis(4-methoxyphenyl)thiourea was utilized to improve the buried interface, leading to a certified efficiency of 23.75% for blade-coated perovskite solar cell.The perovskite solar module (aperture area: 60.84 cm2) demonstrates an efficiency of 20.18% with excellent operational stability (maximum power point tracking of T90 > 1000 h).

Sputter-deposited TiOx thin film as a buried interface modification layer for efficient and stable perovskite solar cells

Despite perovskite solar cells (PSCs) based on a SnO2 hole-blocking layer (HBL) are achieving excellent performance, the non-perfect buried interface between the SnO2 HBL and the perovskite layer is still an obstacle in achieving further improvement in power conversion efficiency (PCE) and stability. The poor morphology with numerous defects and the energy level mismatch at the buried interface constrain the open circuit voltage and cause instability. Herein, a sputter-deposited TiOx thin film is used as a buried interface modification layer to address the aforementioned issues. Utilizing in situ grazing-incidence small-angle X-ray scattering (GISAXS) during the sputter deposition, we monitor and unveil the growth process of the TiOx thin film, identifying a 10 nm thickness optimum. The defects at the buried interface are passivated through tuning the growth, leading to a suppressed non-radiative recombination and improved PCE (from 22.19 % to 23.93 %). The evolution of the device performance and the degradation process of PSCs using operando grazing-incidence wide-angle X-ray scattering (GIWAXS) under the protocol ISOS-L-1I explains the enhanced stability introduced by the buried interface modification via a sputter-deposited TiOx thin layer. The perovskite decomposition process and the detrimental formation of PbI2 are both slowed down by the TiOx thin layer.

Buried interface management for FAPbI3-based perovskite solar cells via multifunctional benzothiadiazole derivatives

Attaining high efficiency in perovskite solar cells (PSCs) often necessitates effective interfacial passivation, which poses challenges, especially concerning the buried interface due to the dissolution of passivation agents during perovskite deposition. In this work, we report a multifunctional modification strategy by introducing the variations of benzothiadiazole (BTD) derivatives to function as interface-modified layers in PSCs. This buried interface modification mitigates oxygen vacancies on the SnO2 surface and fine-tunes the energy level of the electron transport layer, resulting in an improved alignment with the FAPbI3 layer. Furthermore, the introduced BTD derivatives led to the improved crystallinity of FAPbI3 films as well as suppressed the non-radiative recombination losses through passivating the interfacial defects. Consequently, a device with modified SnO2 exhibited an enhanced power conversion efficiency (PCE) of 25.04% along with an improved long-term device stability.

Regulation of the Buried Interface to Achieve Efficient HTL-Free All-Inorganic CsPbI2Br-Based Perovskite Solar Cells.

The large voltage loss (Vloss) mainly stems from the mismatch between the perovskite film and electron transport layer in CsPbI2Br-based all-inorganic perovskite solar cells (I-PSCs), which restricts the power conversion efficiency (PCE) of devices. To address this issue, potassium benzoate (BAP) is first introduced as a bifunctional passivation material to regulate the TiO2/CsPbI2Br interface, reduce the Vloss, and improve the photovoltaic performance of CsPbI2Br-based I-PSCs. Eventually, the champion PCE of CsPbI2Br-based I-PSCs without a hole transport layer modified by BAP (Target-PSCs) improves to 14.90% from the 12.14% of reference PSCs. The open-circuit voltage (Voc) increases to 1.27 V from the initial 1.14 V after BAP modification. A series of characterizations show that BAP modification can not only optimize the energy level alignment of I-PSCs but also passivize the surface defects caused by uncoordinated Cs+/Pb2+. Moreover, the Target-PSCs without encapsulation demonstrate better thermal stability, which can maintain 107.6% of the original PCE after annealing at 160 °C for 140 min in humid air. While the reference PSCs only maintain 76.5% of their initial PCE after annealing at the same process. This work provides a simple strategy to modify the buried interface and improve the performance of CsPbI2Br-based I-PSCs.

Optical Extinction-Based 3D Nano-Imaging of WS2 on Gold.

Broadband nanoextinction images recorded in tip-enhanced optical spectroscopy geometry track the 3D topography of a single layer of WS2 on Au substrate. The described nano-optical method is complementary to conventional atomic force microscopy and offers additional information about the buried material-metal interface that is not accessible using conventional topographic imaging. Beyond 3D optical imaging, we observe large variations in the junction plasmon resonance on the nanoscale. The latter is important to understand and account for in tip-enhanced Raman and photoluminescence studies that target low-dimensional materials specifically. Our observations and (coherent) optical scattering-based method are also relevant to emerging efforts aimed at exploring strong coupling and Fano interferences in hybrid plasmonic-low dimensional quantum material systems.

Study on the enhancement of device performance by the action of carbonohydrazide at the buried bottom interface of inverted mesoporous perovskite solar cells

The interface of perovskite solar cells (PSCs) significantly influences their efficiency and stability. Researchers tend to pay more attention to the upper surface of the perovskite absorber layer and conduct relatively less research on the bottom buried interface, mainly because the bottom of the perovskite film is challenging to peel off, which increases the difficulty of the characterization of the observation and analysis. Defects at the bottom interface make it more challenging to optimize the treatment than the upper surface. For inverted PSCs, the interface located in direct contact between the light absorption layer of perovskite and the hole transport layer is the buried interface. The buried interface is the direct interface for transporting charge carriers of PSCs and is also the center of non-radiative compound enrichment. The defect density is higher than the defect density of perovskite film crystal. Due to the DMSO initially left in the commonly used perovskite precursor solution during the film formation process, evaporation during the annealing and crystallization process creates vacancy holes at the bottom of the perovskite layer film. These holes and crystal boundaries tend to produce many non-radiative recombinations. These holes are also the sites of photodecomposition, leading to reduced efficiency and stability in PSCs, ultimately impacting the overall performance of PSCs. The work adds an Al2O3 mesoporous layer on top of the hole transport layer (HTL), which reduces the direct contact area between PTAA and perovskite film. In the perovskite precursor solution, we incorporate a solid additive called Carbonohydrazide (CBH), this substance replaces some of the DMSO and fills in the voids at the bottom of the perovskite film that is left when the DMSO evaporates. This process helps to reduce non-radiative recombination and photodegradation caused by the voids at the bottom of the perovskite, leading to an improvement in the efficiency and stability of the cell. The optimization of the buried bottom interface has improved the cell’s average efficiency from 17.6 % to 19.7 %, an 11.9 % increase. The aperture area of the devices in this work is 0.048 cm2, and the photoelectric conversion efficiency of our device still reaches 80.64 % of the initial efficiency after 600 h of continuous heating in a glove box with a nitrogen atmosphere, maintaining a test temperature of 60 °C.

Redox reaction at buried ZnO/Ti thin film interface as seen by hard x-ray photoemission and thermal desorption spectroscopy

In the context of low-emissivity glazing, the redox reaction at a buried ZnO/Ti interface is studied in model nanometer-thick film stacks synthesized by magnetron sputtering deposition. For a given amount of Ti, the roles of annealing temperature up to 550 °C, of ZnO layer thickness, and of its crystalline quality are explored. The main originality of the approach is the use of hard x-ray photoemission spectroscopy to probe in situ chemical reactions at a buried interface in a non-destructive way. The detailed analysis of relevant core levels reveals the formation of a ZnxTiyOz ternary compound and the nearly complete oxidation of Ti into TiO2. Thanks to complementary measurements of thermal desorption spectroscopy and electron probe microanalysis, unexpected diffusion of the Zn redox reaction by-product through the upper part of the stack and its desorption in vacuum are clearly evidenced. The reaction and mass transport pathways are rationalized through thermodynamic simulations.

Bottom Contact Engineering for Ambient Fabrication of >25% Durable Perovskite Solar Cells.

The bottom contact in perovskite solar cells (PSCs) is easy to cause deep trap states and severe instability issues, especially under maximum power point tracking (MPPT). In this study, sodium gluconate (SG) is employed to disperse tin oxide (SnO2) nanoparticles (NPs) and regulate the interface contact at the buried interface. The SG-SnO2 electron transfer layer (ETL) enabled the deposition of pinhole-free perovskite films in ambient air and improved interface contact by bridging effect. SG-SnO2 PSCs achieved an impressive power conversion efficiency (PCE) of 25.34% (certified as 25.17%) with a high open-circuit voltage (VOC) exceeding 1.19V. The VOC loss is less than 0.34V relative to the 1.53eV bandgap, and the fill factor (FF) loss is only 2.02% due to the improved contact. The SG-SnO2 PSCs retained around 90% of their initial PCEs after 1000h operation (T90 = 1000h), higher than T80 = 1000h for the control SnO2 PSC. Microstructure analysis revealed that light-induced degradation primarily occurred at the buried holes and grain boundaries and highlighted the importance of bottom-contact engineering.

Lead Iodide Redistribution Enables In Situ Passivation for Blading Inverted Perovskite Solar Cells with 24.5% Efficiency.

Blade-coating stands out as an alternative for fabricating scalable perovskite solar cells. However, it demands special control of the precursor composition regarding nucleation and crystallization and currently exhibits lower performance than the spin-coating process. It is mainly the resulting film morphology and excess lead iodide (PbI2) distribution that influences the optoelectronic properties. Here, the effectiveness of introducing N-Methyl-2-pyrrolidone (NMP) to regulate the structure of the perovskite layer and the redistribution of PbI2 is found. The introduction of NMP leads to the accumulation of excess PbI2, mainly on the top surface, reducing residual PbI2 at the perovskite buried interface. This not only facilitates the passivation of perovskite grain boundaries but also eliminates the potential degradation of the PbI2 triggered by light illumination in the perovskite buried interface. The optimized NMP-modified inverted perovskite solar cell achieves a champion efficiency of 24.5%, among the highest reported blade-coated perovskite solar cells. Furthermore, 13.68cm2 blading perovskite solar modules are fabricated and demonstrate an efficiency of up to 20.4%. These findings underscore that with proper modulation of precursor composition, blade-coating can be a feasible and superior alternative for manufacturing high-quality perovskite films, paving the way for their large-scale applications in photovoltaic technology.

Dipropyl sulfide optimized buried interface to improve the performance of inverted perovskite solar cells

Recently, [4–(3,6-dimethyl-9H-carbazol-9-yl)butyl] phosphonic acid (Me-4PACz) has garnered significant attention as a highly effective passivation layer for NiOx. However, the Me-4PACz passivation layer shows low wettability to perovskite precursors, hindering the crystallization of perovskite. Moreover, Me-4PACz does not uniformly and completely cover NiOx, failing to achieve an optimal passivation effect. The presence of high-valence-state Ni species and reactive hydroxyls on the NiOx film surface leads to perovskite degradation. To address this, dipropyl sulfide (DPS) was incorporated into a solution of Me-4PACz. This approach not only enhances the wettability of Me-4PACz, facilitating the growth of larger perovskite grains but also enables Me-4PACz to form a homogeneous passivation layer with strong coverage. This effectively prevents direct contact between NiOx and perovskite films. Additionally, DPS interacts with reactive hydroxyls, removing them from the NiOx surface and mitigating the deprotonation reaction of MA/FA in perovskite. Furthermore, DPS is reducible, which helps in reducing high-valent Ni (Ni4+), thereby decreasing redox reactions at the interface. As a result, the optimized perovskite solar cells with DPS achieved a power conversion efficiency (PCE) of 22.29%, higher than the control device of 20.52%. Moreover, the DPS-decorated device demonstrated excellent stability, retaining over 80% of its initial PCE value, compared to only 60% retention in the control device. This work modified the buried interface and offers valuable insights for subsequent similar studies.

Perovskite Crystallization Control for Large, Oriented Grains with Residual Solvent Restrain via Hydrogen-Bonded Organic Frameworks.

Void-free perovskite films with oriented large grains are considered good performance. However, contradictory requirements on solvent volatilization arise that the growth of large grains requires slow volatilization while the residual solvent problem, which leads to difficult-handled voids at buried interface, requires quick and complete volatilization. Currently, although grain boundaryadditives help reach large and oriented grains, the occupation of additives in the grain boundary volatilization channel may further deteriorate the residual solvent problem. Herein, porous structures with "switchable pore" nature are constructed based on flexible hydrogen-bonded (HOF-FJU-2) in perovskite grain boundaries to meet both contradictory requirements with achieving crystallization control and residual solvent restrain. The additive moleculesprolongs the perovskite crystallization through the Pb-O bond and guides the growth of (100) facet based on its strong ordered accumulation trend. The pre-embedded porous structure opens up the solvent volatilization channel for complete volatilization in annealing stage and then switches to a closed pore state via phase transformation after the solvent completely leaves, preventing the intrusion of the external environment. Combined with theoretical calculations and in situ spectrum tests, the crystallization thermodynamics and dynamics are analyzed. As expected, the target device exhibits enhanced performance (improved from 22.14% to 24.18%) and stability.

Stepwise Crystallization and Mass Transport Limitations in Annealed SPEEK Thin Films

Pt-supported SPEEK (sulfonated poly ether ether ketone) thin films, mimicking the ionomer-electrode interface in polymer electrolyte fuel cells (PEFCs), were synthesized with thicknesses from 12 to 105 nm. Their glass transition temperature (Tg) was analyzed via in-situ thermal ellipsometry, revealing a thickness-dependent Tg decrease, indicative of confinement effects. Particularly, a 30 nm film, typical of practical ionomer films, exhibited surface crystallization preceding that at the buried interface, a phenomenon linked to higher mobility at the free surface, as con-firmed by grazing incidence wide-angle X-ray scattering (GI-WAXS) at both sub-critical (0.09º) and supercritical (0.14º) angles. This study elucidates the dynamic interplay between the high-mobility free surface and the interaction-intensive buried interface in confined SPEEK thin films. It was observed that below 30 nm thickness, interfacial interactions become the primary factor influencing transition temperature. Additionally, spatially heterogeneous crystallization, more pronounced in the out-of-plane direction, correlates with reduced proton conduction.