Removal of Surface Oxygen Vacancies Increases Conductance Through TiO2 Thin Films for Perovskite Solar Cells

Oxygen Vacancy Mediation in SnO2 Electron Transport Layers Enables Efficient, Stable, and Scalable Perovskite Solar Cells

Previous findings have suggested a close association between oxygen vacancies in SnO2 and charge carrier recombination as well as perovskite decomposition at the perovskite/SnO2 interface. Underlying the fundamental mechanism holds great significance in achieving a more favorable balance between the efficiency and stability. In this study, we prepared three SnO2 samples with different oxygen vacancy concentrations and observed that a low oxygen vacancy concentration is conducive to long-term device stability. Iodide ions were observed to easily diffuse into regions with high oxygen vacancies, thereby speeding up the deprotonation of FAI, as made evident by the detection of the decomposition product formamide. In contrast, a high oxygen vacancy concentration in SnO2 could prevent hole injection, leading to a decrease in interfacial recombination losses. To suppress this decomposition reaction and address the trade-off, we designed a bilayer SnO2 structure to ensure highly efficient carrier transport still while maintaining a chemically inert surface. As a result, an enhanced efficiency of 25.06% (certified at 24.55% with an active area of 0.09 cm2 under fast scan) was achieved, and the extended operational stability maintained 90% of their original efficiency (24.52%) after continuous operation for nearly 2000 h. Additionally, perovskite submodules with an active area of 14 cm2 were successfully assembled with a PCE of up to 22.96% (20.09% with an aperture area).

Defect Engineering at Buried Interface of Perovskite Solar Cells

Perovskite solar cells (PSC) have developed rapidly since the past decade with the aim to produce highly efficient photovoltaic technology at a low cost. Recently, physical and chemical defects at the buried interface of PSC including vacancies, impurities, lattice strain, and voids are identified as the next formidable hurdle to the further advancement of the performance of devices. The presence of these defects has unfavorably impacted many optoelectronic properties in the PSC, such as band alignment, charge extraction/recombination dynamics, ion migration behavior, and hydrophobicity. Herein, a broad but critical discussion on various essential aspects related to defects at the buried interface is provided. In particular, the defects existing at the surface of the underlying charge transporting layer (CTL) and the bottom surface of the perovskite film are initially elaborated. In situ and ex situ characterization approaches adopted to unveil hidden defects are elucidated to determine their influence on the efficiency, operational stability, and photocurrent-voltage hysteresis of PSC. A myriad of innovative strategies including defect management in CTL, the introduction of passivation materials, strain engineering, and morphological control used to address defects are also systematically elucidated to catalyze the further development of more efficient, reliable, and commercially viable photovoltaic devices.

Reduced Work Function in Anatase ⟨101⟩ TiO2 Films Self-Doped by O-Vacancy-Dependent Ti3+ Bonds Controlling the Photocatalytic Dye Degradation Performance

TiO2 has the proven capability of catalytically decomposing pollutants under light illumination, thereby embracing potential applications in wastewater management. The photocatalytic dye degradation activity is largely controlled by the optical band gap that dictates the extent of electron-hole pair generation via photon absorption, and the recombination kinetics of charges. In this context, the material's work function governs how easily the charge carriers can be transferred at the dye-adsorbed photocatalytically active sites. Accordingly, nanocrystalline TiO2 thin films are grown in the anatase phase with ⟨101⟩ orientation, using RF magnetron sputtering at 200 °C. Besides studying the film's structural morphology, optical band gap, and elemental composition, the electronic properties are extensively investigated. The work function of the material was controlled by varying the O-vacancy-dependent Ti3+ bonding configuration in the network. It has been demonstrated how the photocatalytic methylene blue dye degradation activity of the nanocrystalline TiO2 films of predominantly the anatase phase improves on reducing the sputtering pressure during deposition. At a low deposition pressure of 20 mTorr, a low work function of ∼4.2 eV of the film, resulting from the formation of a Ti3+-bond through the O vacancies in the network, potentially increases its carrier lifetime and delivers the superior photocatalytic activity (∼82.7% dye degradation with a rate constant of k ∼ 0.0073 min-1) via silently facilitating fast electron transfer from the photocatalyst to the dye in the aqueous solution. The higher stoichiometric film prepared at p = 40 mTorr exhibits an inferior photocatalytic activity (∼20.4% dye degradation with a rate constant of k ∼ 0.0009 min-1), as retarded by its higher work function of ∼4.62 eV, despite retaining a relatively low band gap. Thus, without using any heterojunction or extrinsically doped photocatalyst, the dye degradation can be controlled simply by reducing the work function of nanocrystalline TiO2 thin films via controlling the O-vacancy-dependent Ti3+ bonding in its self-doped network.

Nickel Oxide Hole Injection Layers for Balanced Charge Injection in Quantum Dot Light-Emitting Diodes

Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation displays, but suffer from carrier imbalance arising from lower hole injection compared to electron injection. A defect engineering strategy is reported to tackle transport limitations in nickel oxide-based inorganic hole-injection layers (HILs) and find that hole injection is able to enhance in high-performance InP QLEDs using the newly designed material. Through optoelectronic simulations, how the electronic properties of NiOx affect hole injection efficiency into an InP QD layer, finding that efficient hole injection depends on lowering the hole injection barrier and enhancing the acceptor density of NiOx is explored. Li doping and oxygen enriching are identified as effective strategies to control intrinsic and extrinsic defects in NiOx, thereby increasing acceptor density, as evidenced by density functional theory calculations and experimental validation. With fine-tuned inorganic HIL, InP QLEDs exhibit a luminance of 45 200 cd m-2 and an external quantum efficiency of 19.9%, surpassing previous inorganic HIL-based QLEDs. This study provides a path to designing inorganic materials for more efficient and sustainable lighting and display technologies.

Influence of oxygen vacancies, surface composition, and crystallite size on the photoelectrochemical oxidation activity of C,N-codoped TiO2 for cefadroxil abatement along with O3

This study aims the development of photoelectrodes to be incorporated in a photoelectrocatalytic ozonation (PECO) process for tertiary treatment of urban wastewaters, targeting the removal of contaminants of emerging concern (CEC). PECO tests were performed using urban wastewater after secondary treatment fortified with Cefadroxil (CFX, C16H17N3O5S), as target model CEC. Three Nitrogen and Carbon doped TiO2 (CN-TiO2) electrodes were synthesized by anodizing at 50, 70, and 90 V, and calcined. These materials were characterized by X-Ray diffraction and Rietveld refinement, Scanning Electron Microscopy, Diffuse Reflectance Spectroscopy, X-ray photoelectron spectroscopy, chronoamperometry, and electrochemical impedance spectroscopy, to correlate defects with photoactivity. All photoanodes considerably reduced their main bandgaps by the incorporation of C and N species, to enable absorption capacities in the UV region using a Xe lamp. The lowest oxygen vacancy content and largest crystallite size were found for CN-TiO2-70, favoring the reduction of bulk defects that could act as recombination of charge carriers. Therefore, oxygen vacancies affect more the TiO2 photoactivity compared to the crystallite size or the light absorption capacity, confirming that a lower content of vacancies in the material bulk and surface doping significantly influence the activity as detected by Rietveld refinement, DRS, and XPS. The electrochemical techniques confirm that the highest photocurrent was obtained for CN-TiO2-70, whence this photoanode was chosen to carry out the CFX degradation. A point defect model simulating Nyquist plot reveals that the photoactivity depends on the speed to diffuse oxygen vacancies through the TiO2 coating. All abatement processes were followed by high-performance liquid chromatography, and Total Organic Carbon (TOC). At neutral and alkaline conditions, CFX is eliminated to levels below the analytical detection limit after 90 min of treatment (TOC removals of 87 and 91%, respectively), indicating that the coupling between the CN-TiO2-70 photocatalyst and ozone is effective in eliminating the contaminant due to parallel routes forming •OH species. Lower CFX degradation observed at acidic pH (TOC removal of 70%) is assigned to the difficulty of oxidizing protonated CFX species.

Stratified Oxygen Vacancies Enhance the Performance of Mesoporous TiO2 Electron Transport Layer in Printable Perovskite Solar Cells

The low electrical conductivity and the high surface defect density of the TiO2 electron transport layer (ETL) limit the power conversion efficiency (PCE) of corresponding perovskite solar cells (PSCs). Here, the conductivity and defect modulation of the mesoporous TiO2 (mp-TiO2 ) ETL via oxygen vacancy (OV) management by the reduction and oxidation treatment are reported. Reduction treatment via reducing agent introduces abundant OVs into the TiO2 nanocrystalline particles on the surface and at the subsurface. The following oxidation treatment via hydrogen peroxide removes the surface OVs while remains the subsurface OVs, resulting in stratified OVs. The stratified OVs improve the conductivity of TiO2 ETL by increasing carrier donors and decrease nonradiative centers by reducing surface defects. Such synergy ensures the capability of mp-TiO2 as the well-performed ETL with improved energy level alignment, suppressed interface recombination, enhanced carrier extraction, and transport. As a result, printable hole-conductor-free carbon-based mesoscopic PSCs based on the modulated mp-TiO2 ETL demonstrate a highest reported PCE of 18.96%.

Recovery of oxidized two-dimensional MXenes through high frequency nanoscale electromechanical vibration

MXenes hold immense potential given their superior electrical properties. The practical adoption of these promising materials is, however, severely constrained by their oxidative susceptibility, leading to significant performance deterioration and lifespan limitations. Attempts to preserve MXenes have been limited, and it has not been possible thus far to reverse the material's performance. In this work, we show that subjecting oxidized micron or nanometer thickness dry MXene films-even those constructed from nanometer-order solution-dispersed oxidized flakes-to just one minute of 10 MHz nanoscale electromechanical vibration leads to considerable removal of its surface oxide layer, whilst preserving its structure and characteristics. Importantly, electrochemical performance is recovered close to that of their original state: the pseudocapacitance, which decreased by almost 50% due to its oxidation, reverses to approximately 98% of its original value, with good capacitance retention ( ≈ 93%) following 10,000 charge-discharge cycles at 10 A g^-1. These promising results allude to the exciting possibility for rejuvenating the material for reuse, therefore offering a more economical and sustainable route that improves its potential for practical translation.

Cancer Stem Cell Derived Extracellular Vesicles with Self-Functionalized 3D Nanosensor for Real-Time Cancer Diagnosis: Eliminating the Roadblocks in Liquid Biopsy

Liquid biopsy for determining the presence of cancer and the underlying tissue of origin is crucial to overcome the limitations of existing tissue biopsy and imaging-based techniques by capturing critical information from the dynamic tumor heterogeneity. A newly emerging liquid biopsy with extracellular vesicles (EVs) is gaining momentum, but its clinical relevance is in question due to the biological and technical challenges posed by existing technologies. The biological barriers of existing technologies include the inability to generate fundamental details of molecular structure, chemical composition as well as functional variations in EVs by gathering simultaneous information on multiple intra-EV molecules, unavailability of holistic qualitative analysis, in addition to the inability to identify tissue of origin. Technological barriers include reliance on EV isolation with a few labeled biomarkers, resulting in the inability to generate comprehensive information on the disease. A more favorable approach would be to generate holistic information on the disease without the use of labels. Such a marker-free diagnosis is impossible with the existing liquid biopsy due to the unavailability clinically validated cancer stem cells (CSC)-specific markers and dependence of existing technologies on EV isolation, undermining the clinical relevance of EV-based liquid biopsy. Here, CSC EVs were employed as an independent liquid biopsy modality. We hypothesize that tracking the signals of CSCs in peripheral blood with CSC EVs will provide a reliable solution for accurate cancer diagnosis, as CSC are the originators of tumor contributing to tumor heterogeneity. We report nanoengineered 3D sensors of extremely small nano-scaled probes self-functionalized for SERS, enabling integrative molecular and functional profiling of otherwise undetectable CSC EVs. A substantially enhanced SERS and ultralow limit of detection (10 EVs per 10 μL) were achieved. This was attributed to the efficient probe-EV interaction due to the 3D networks of nanoprobes, ensuring simultaneous detection of multiple EV signals. We experimentally demonstrate the crucial role of CSC EVs in cancer diagnosis. We then completed a pilot validation of this modality for cancer detection as well as for identification of the tissue of origin. An artificial neural network distinguished cancer from noncancer with 100% sensitivity and 100% specificity for three hard to detect cancers (breast, lung, and colorectal cancer). Binary classification to distinguish one tissue of origin against all other achieved 100% accuracy, while simultaneous identification of all three tissues of origin with multiclass classification achieved up to 79% accuracy. This noninvasive tool may complement existing cancer diagnostics, treatment monitoring as well as longitudinal disease monitoring by validation with a large cohort of clinical samples.

The Potential Effect of Annealing Mesostructured Titanium Dioxide Electrode in a Closed Box Furnace on the Concentration of Lead (II) Iodide Solution Required for Optimal Performance of Mesoscopic Perovskite Solar Cells

Highly reproducible mesoscopic perovskite solar cells (PSCs) can be fabricated using two-step sequential deposition of organo-lead halide (perovskite) active layer. However, differences in the processing conditions of individual layers which are subsequently assembled to construct the ultimate device can result in variations in the solar cell performance. For instance, here we report trends in the device performance as a function of PbI2 solution concentration, where the compact and mesoporous TiO2 layers were annealed in a closed box furnace (instead of doing it in open air). We observed that the devices prepared using 1.2 M PbI2 solution concentration performed better than those prepared from 0.8 M and 1 M PbI2 solutions. Generally, the researchers use the hot plate in an open-air environment or use a special hot plate where a continuous flow of air is ensured while annealing TiO2 electron selective layers (ESL) for perovskite solar cells. In this case, the highest possible device efficiencies are achieved using 1 M concentration of PbI2 solution. Although the influence of PbI2 solution concentration has been previously studied in detail, here our prime focus is to briefly comment on slight differences in the device performance trends which we observed in comparison to the previously reported results, where TiO2 layers were calcined in open air.

Single-crystalline TiO2 nanoparticles for stable and efficient perovskite modules

Despite the remarkable progress in power conversion efficiency of perovskite solar cells, going from individual small-size devices into large-area modules while preserving their commercial competitiveness compared with other thin-film solar cells remains a challenge. Major obstacles include reduction of both the resistive losses and intrinsic defects in the electron transport layers and the reliable fabrication of high-quality large-area perovskite films. Here we report a facile solvothermal method to synthesize single-crystalline TiO₂ rhombohedral nanoparticles with exposed (001) facets. Owing to their low lattice mismatch and high affinity with the perovskite absorber, their high electron mobility and their lower density of defects, single-crystalline TiO₂ nanoparticle-based small-size devices achieve an efficiency of 24.05% and a fill factor of 84.7%. The devices maintain about 90% of their initial performance after continuous operation for 1,400 h. We have fabricated large-area modules and obtained a certified efficiency of 22.72% with an active area of nearly 24 cm², which represents the highest-efficiency modules with the lowest loss in efficiency when scaling up.

Laser-Assisted Ultrafast Fabrication of Crystalline Ta-Doped TiO2 for High-Humidity-Processed Perovskite Solar Cells

A titanium dioxide (TiO₂) compact film is a widely used electron transport layer (ETL) for n-i-p planar perovskite solar cells (PSCs). However, TiO₂ sufferers from poor electrical conductivity, leading to high energy loss at the perovskite/ETL/transparent conductive oxide interface. Doping the TiO₂ film with alkali- and transition-metal elements is an effective way to improve its electrical conductivity. The conventional method to prepare these metal-doped TiO₂ films commonly requires time-consuming furnace treatments at 450-600 °C for 30 min to 3 h. Herein, a rapid one-step laser treatment is developed to enable doping of tantalum (Ta) in TiO₂ (Ta-TiO₂) and to simultaneously induce the crystallization of TiO₂ films from its amorphous precursor to an anatase phase. The PSCs based on the Ta-TiO₂ films treated with the optimized fiber laser (1070 nm) processing parameters (21 s with a peak processing temperature of 800-850 °C) show enhanced photovoltaic performance in comparison to that of the device fabricated using furnace-treated films at 500 °C for 30 min. The ambient-processed planar PSCs fabricated under high relative humidity (RH) of 50-70% display power conversion efficiencies (PCEs) of 18.34% and 16.04% for devices based on Cs_0.1FA_0.9PbI₃ and CH₃NH₃PbI₃ absorbers, respectively. These results are due to the improved physical and chemical properties of the Ta-TiO₂ films treated by the optimal laser process in comparison to those for the furnace process. The laser process is rapid, simple, and potentially scalable to produce metal-doped TiO₂ films for efficient PSCs.

Tracking the Evolution of Metastasis with Self-Functionalized 3D Nanoprobes

Despite recent advances in cancer treatment, metastasis is the cause of mortality in 90% of cancer cases. It has now been well-established that dissemination of cancer cells to distant sites occurs very early during tumorigenesis, resulting in the minimal effect of surgical or chemotherapeutic treatments after the detection of metastasis. The underlying reason for this challenge is mostly due to the limited understanding of molecular mechanisms of the metastasis cascade, particularly related to metastatic traits. Therefore, there is an urgent need to investigate this currently invisible evolution of metastasis. The tracking of metastasis evolution has not been addressed yet. Here, we introduce, for the first time, a synchronous approach to unveil the molecular mechanisms of the metastasis cascade. As cancer stem cells (CSCs) demonstrate cancer initiation, drug resistance, metastasis, and tumor relapse and can exist in a quasi-intermediate epithelial-mesenchymal transition state, the tumor-initiating events during a CSCs metamorphosis were monitored with single-cell sensitivity. Because of the invasive and resistive properties of the metastable intermediate CSCs, investigation of the molecular profiles of the quasi-intermediate CSCs was necessary for the detection of metastasis dissemination. For this purpose, the ultrasensitive technique of surface-enhanced Raman scattering (SERS) was adopted. Titanium-based, biocompatible three-dimensional (3D) nanoprobes that were synthesized for multiphoton ionization achieved a substantial SERS enhancement of ∼80-fold due to the oxygen vacancy-enriched composition of the nanoprobes. The 3D interconnected complex nanoarchitecture of the nanoprobes enabled us to entrap the nonadherent CSCs of three metastatic cancer cell lines (triple negative breast adenocarcinoma (MDAMB231), human Caucasian colon adenocarcinoma (COLO 205), and cervical adenocarcinoma (HeLa)─all very aggressive forms of cancer). The nanoprobes not only promoted the CSC proliferation to successfully attain the quasi-intermediate states but also monitored its reprogramming into a cancer cell state. The nanoprobes substantially amplified weak intracellular Raman signals to capture the molecular events during a CSC transformation. The detection of cancer was achieved with 100% accuracy. We experimentally demonstrated that the molecular signatures of CSC reprogramming are cancer-type specific. This observation enabled us to identify the origin of metastasis with 100% accuracy, providing more clarity on the relatively unknown quasi-intermediate states. This first demonstration of CSC-based tracking of metastasis evolution has the potential to provide an insightful perspective of tumorigenesis that could be useful in cancer diagnosis and prognosis as well as in the monitoring of therapeutic interventions.

Metal oxide charge transporting layers for stable high-performance perovskite solar cells

This review summarizes the recent progress in metal oxide charge transporting layers to achieve stable high-performance perovskite solar cells.

Hydration Dynamics and the Future of Small-Amplitude AFM Imaging in Air

Here, we discuss the effects that the dynamics of the hydration layer and other variables, such as the tip radius, have on the availability of imaging regimes in dynamic AFM-including multifrequency AFM. Since small amplitudes are required for high-resolution imaging, we focus on these cases. It is possible to fully immerse a sharp tip under the hydration layer and image with amplitudes similar to or smaller than the height of the hydration layer, i.e., ~1 nm. When mica or HOPG surfaces are only cleaved, molecules adhere to their surfaces, and reaching a thermodynamically stable state for imaging might take hours. During these first hours, different possibilities for imaging emerge and change, implying that these conditions must be considered and reported when imaging.

Boosting the sub-cellular biomolecular cancer signals by self-functionalized tag-free nano sensor

Surface Enhanced Raman Scattering (SERS)-based sub-cellular cancer diagnosis can simultaneously obtain multiple biomolecular signals crucial in diagnostic platform for a heterogeneous disease like cancer. But, SERS-probes being typically tagged with chemical functionalization demonstrate limitations due to adverse biocompatibility, ineffective cellular internalization, SERS-signal quenching and spectral contamination. Although, tag-free SERS-probes overcome these limitations; complexity in spectral interpretation and detection insensitivity make it disadvantageous. In this study, we have exploited the inherent charges of cellular biomolecules and introduced self-functionalized complementary charged, tag-free SERS nano probes for biomolecule-specific investigation. Extremely small nano probes (sub 10 nm), synthesized with multiphoton ionization were functionalized with charge by physical synthesis without any ligands or chemical processes. The probes demonstrated significant SERS (EF~10⁶) with analyte molecules (4ATP & 4MBA). Multifold signal boost was achieved for the signals of cellular components - amplification of ~7 fold for DNA, ~16 fold for proteins and ~24 fold for lipids with the commentary charged nano probes as compared to the neutral nano probes. The signal boost was attributed to the efficient delivery of extremely small, complementary charged probes to the cellular biomolecules of interest enabling simultaneous detection of sub-cellular biomolecules such as DNA, proteins and lipids and with high reproducibility. Cancer classification and investigation of drug resistance in cancer with single cell sensitivity was demonstrated. Such biomolecule-specific investigation of cancer from intact cells will open pathways for comprehensive cancer diagnosis.

Flame Synthesized Blue TiO2- x with Tunable Oxygen Vacancies from Surface to Grain Boundary to Bulk

Fabrication of nonstoichiometric metal oxides containing oxygen vacancies (OVs) has been an effective strategy to modulate their (photo)catalytic or (photo)electrochemical performances which are all affected by charge transfer at the interface and in the bulk. Considerable efforts are still needed to achieve tunability of OVs, as well as their quantitative characterization. Herein, a one-step flame synthesis method is reported for the first time for fast fabrication of blue TiO_{2- x} with controllable defect content and location. Temperature-programmed oxidation (TPO) analysis is applied for the first time and found to be an excellent technique in both differentiating and quantifying OVs at the surface, grain boundary (GB), and bulk of TiO_{2- x} . The results indicate that a moderate level of OVs can greatly enhance the charge transfer. Importantly, the OVs locked at GBs due to the thermal sintering of nanoparticles during the synthesis can facilitate the anchoring and reduction of Pt species.

Ambient Fabrication of Organic-Inorganic Hybrid Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted significant attention in recent years due to their high-power conversion efficiency, simple fabrication, and low material cost. However, due to their high sensitivity to moisture and oxygen, high efficiency PSCs are mainly constructed in an inert environment. This has led to significant concerns associated with the long-term stability and manufacturing costs, which are some of the major limitations for the commercialization of this cutting-edge technology. Over the past few years, excellent progress in fabricating PSCs in ambient conditions has been made. These advancements have drawn considerable research interest in the photovoltaic community and shown great promise for the successful commercialization of efficient and stable PSCs. In this review, after providing an overview to the influence of an ambient fabrication environment on perovskite films, recent advances in fabricating efficient and stable PSCs in ambient conditions are discussed. Along with discussing the underlying challenges and limitations, the most appropriate strategies to fabricate efficient PSCs under ambient conditions are summarized along with multiple roadmaps to assist in the future development of this technology.

TiO2 with controllable oxygen vacancies for efficient isopropanol degradation: photoactivity and reaction mechanism

Flame-synthesized TiO_2−x with controllable defects exhibits a remarkable photooxidation efficiency of gaseous isopropanol with the reaction mechanism investigated.

Electronic effects of nano-confinement in functional organic and inorganic materials for optoelectronics

This review provides a comprehensive overview of the electronic effects of nano-confinement (from 1D to 3D geometries) on optoelectronic materials and their applications.

The dual interfacial modification of 2D g-C3N4 for high-efficiency and stable planar perovskite solar cells

Carrier recombination and charge loss at the interfaces of perovskite layers have a significant influence on high-performance planar perovskite solar cells (PSCs). We employed two-dimensional graphitic carbon nitride (g-C₃N₄), which is a heat-resistant n-type semiconductor, to modify the electron-transport layer/perovskite and perovskite/hole-transport layer interfaces, respectively. g-C₃N₄ could passivate the surface trap states of the methylammonium lead iodide light absorber through the formation of a Lewis adduct between N and the under-coordinated Pb, and it could also remarkably reduce the grain boundaries between perovskite crystal particles. A maximum power conversion efficiency (PCE) of 19.67% (V _oc = 1.14 V, J _sc = 21.45 mA cm^-2, FF = 0.807) could be obtained from planar PSCs with long-term stability using dual-positioned g-C₃N₄. Therefore, we consider that ultrathin semiconductor films with a Lewis base nature are suitable as dual-functional transport materials for devices. This work provides new guidance for dual-interfacial modification to improve the PCE and stability of devices.

Enhanced Vertical Charge Transport of Homo- and Blended Semiconducting Polymers by Nanoconfinement

The morphology of conjugated polymers has critical influences on electronic and optical properties of optoelectronic devices. Even though lots of techniques and methods are suggested to control the morphology of polymers, very few studies have been performed inducing high charge transport along out-of-plane direction. In this study, the self-assembly of homo- and blended conjugated polymers which are confined in nanostructures is utilized. The resulting structures lead to high charge mobility along vertical direction for both homo- and blended conjugated polymers. Both semicrystalline and amorphous polymers show highly increased population of face-on crystallite despite intrinsic crystallinity of polymers. They result in more than two orders of magnitude enhanced charge mobility along vertical direction revealed by nanoscale conductive scanning force microscopy and macroscale IV characteristic measurements. Moreover, blends of semicrystalline and amorphous polymers, which are known to show inferior optical and electrical properties due to their structural incompatibility, are formed into harmonious states by this approach. Assembly of blends of semicrystalline and amorphous polymers under nanoconfinement shows charge mobility in out-of-plane direction of 0.73 cm² V^-1 s^-1 with wide range of absorption wavelength from 300 to 750 nm demonstrating the synergistic effects of two different polymers.

Atomic Layer Deposition of an Effective Interface Layer of TiN for Efficient and Hysteresis-Free Mesoscopic Perovskite Solar Cells

Perovskite solar cells (PSCs) have experienced outstanding advances in power conversion efficiencies (PCEs) by employing new electron transport layers (ETLs), interface engineering, optimizing perovskite morphology, and improving charge collection efficiency. In this work, we study the role of a new ultrathin interface layer of titanium nitride (TiN) conformally deposited on a mesoporous TiO₂ (mp-TiO₂) scaffold using the atomic layer deposition method. Our characterization results revealed that the presence of TiN at the ETL/perovskite interface improves the charge collection as well as reduces the interface recombination. We find that the morphology (grain size) and optical properties of the perovskite film deposited on the optimized mp-TiO₂/TiN ETL are improved drastically, leading to devices with a maximum PCE of 19.38% and a high open-circuit voltage (V_oc) of 1.148 V with negligible hysteresis and improved environmental (∼40% RH) and thermal (80 °C) stabilities.

Over 20% Efficiency in Methylammonium Lead Iodide Perovskite Solar Cells with Enhanced Stability via "in Situ Solidification" of the TiO2 Compact Layer

In methylammonium lead iodide (MAPbI₃) perovskite solar cells (PSCs), the device performance is strongly influenced by the TiO₂ electron transport layer (ETL). Typically, the ETL needs to simultaneously be thin and pinhole-free to have high transmittance and avoid shunting. In this work, we develop an "in situ solidification" process following spin coating in which the titanium-based precursor (titanium(diisopropoxide) bis(2,4-pentanedionate)) is dried under vacuum to rapidly achieve continuous TiO₂ layers. We refer to this as "gas-phase quenching". This results in thin (60 ± 10 nm), uniform, and pinhole-free TiO₂ films. The PSCs based on the gas-phase quenched TiO₂ exhibits improved power conversion efficiency, with a median value of 18.23% (champion value of 20.43%), compared to 9.03 and 14.09% for the untreated devices. Gas-phase quenching is further shown to be effective in enabling efficient charge transfer at the MAPbI₃/TiO₂ heterointerface. Furthermore, the stability of the gas-phase quenched devices is enhanced in ambient air as well as under 1 sun illumination. In addition, we achieve 12.1% efficiency in upscaled devices (1.1 cm² active area).