Enhanced Self-Assembled Monolayer Surface Coverage by ALD NiO in p-i-n Perovskite Solar Cells

Efficient perovskite solar modules enabled by a UV-stable and high-conductivity hole transport material

Ultraviolet (UV) radiation poses a substantial challenge to the stability of prevalent p-i-n (positive-intrinsic-negative) perovskite solar cells (PSCs), demanding more robust hole-transport layers (HTLs) due to light incident from the HTL side. Here, we unveil that commonly used self-assembled monolayer (SAM)-type HTLs suffer from poor UV stability that causes irreversible damage to hole extraction and impairs device stability. To address this issue, we develop a polymeric and UV-stable HTL named Poly-2PACz, which exhibits strong binding to substrates and exceptional UV resistance over SAM-type HTLs. The PSCs blade-coated under ambient conditions using Poly-2PACz HTL achieved a remarkable efficiency of 26.0% and outstanding UV stability. Our cells retain 80% of the initial PCE even after about 500 hours of high-intensity UV illumination [7.7 times higher than that of air mass 1.5 global (AM 1.5G) solar spectrum]. Furthermore, Poly-2PACz exhibits good wettability and high conductance, enabling the fabrication of blade-coated minimodules with an aperture efficiency of 22.2% and excellent uniformity.

Synergic MXene and S-benzyl-L-cysteine Passivation Strategies for Wide Bandgap Perovskite Solar Cells for 4T Tandem Applications

Bilayer nickel oxide (NiOx)/[2-(3,6-dimethoxy-9H-carbazol-9yl) ethyl] phosphonic acid (MeO-2PACz) hole transport layers have become attractive for perovskite solar cells and tandem architectures. However, challenges such as the instability of NiOx ink, hole accumulation, and trap-assisted non-radiative recombination at the interface remain major drawbacks for using NiOx/MeO-2PACz HTL bilayer. In this work, two synergic strategies are employed to address these issues such as the doping of the NiOx ink with niobium (Nb)-based MXene) and the introduction of S-benzyl-L-cysteine (SBLC) molecule to passivate the MeO-2PACz/perovskite interface. These modifications effectively reduced defect states in the perovskite layer and enhanced the dipole moment of MeO-2PACz, minimizing the valence band offset at the MeO-2PACz/perovskite interface with the reduction of the charge recombination rates. Consequently, the target PSC device, made of 1.68 eV-bandgap perovskite, demonstrated a power conversion efficiency (PCE) of 19.5% and improved stability compared to the control device when tested under ISOS protocols. Furthermore, semi-transparent (ST) PSCs have been fabricated for application in 4T tandem perovskite-silicon cell showing PCE of 18.15% and 27.95% in single-junction and in tandem architectures, respectively. These findings demonstrate the effectiveness of combining strategic doping and passivation techniques for inverted PSCs enhancing the device performance without discarding long-term stability.

Optimizing Molecular Packing and Interfacial Contact via Halogenated N-Glycidyl Carbazole Small Molecules for Low Energy Loss and Highly Efficient Inverted Perovskite Solar Cells

Nonideal interfacial contact and non-radiative voltage loss in self-assembled monolayers (SAMs)-based inverted perovskite solar cells (PSCs) limit their further development. Herein, two carbazole-based molecules with different halogen atoms (X-OCZ, X = Cl or Br) are developed as efficient interfacial regulators. The halogen effect not only finely modulates the molecular packing, crystallinity, and surface contact potential of the MeO-2PACz analogue via self-induced intermolecular interactions but also significantly influences the subsequent crystal growth of perovskite, thus resulting in the formation of high-quality films with enhanced crystallinity, improved energy level alignment, and depressed non-radiative recombination. Importantly, the Cl-OCZ-mediated device exhibits a minimal interfacial carrier transport energy barrier of 0.10 eV and an impressive charge collection efficiency of 93.6%. Moreover, the target device (aperture area: 0.09 cm2) shows an exceptional efficiency of 26.57% (certified 26.4%) along with enhanced thermal and operational stability. The strategy is also extended to large area devices, delivering efficiencies of 25.0% for a 1 cm2 device and 22.9% for a 12.96 cm2 minimodule. This study highlights the halogen role of interfacial small molecules in optimizing molecular packing and interfacial contact toward highly efficient PSCs with minimized energy loss and non-radiative recombination.

Multifunctional Hole Transport Strategy for Highly Efficient and Stable Inverted Perovskite Solar Cells

Self-assembled monolayer (SAM)-based inverted perovskite solar cells (PSCs) have exhibited excellent performance in efficiency, while the stability and reproducibility of the PSCs still need to be improved. In this work, we present a multifunctional hole transport approach for inverted PSCs, where NiOX, SAM ((E)-3-(4-(bis(4-methoxyphenyl)amino)phenyl)acrylic acid, abbreviated as MPTCA) and a wetting agent (2-phenylethylamine hydroiodide, known as PEAI) are employed for hole-transport materials (HTMs). This NiOX/MPTCA/PEAI composite layer is uniform and has good wetting properties, which enables the formation of a high-quality perovskite film, effectively minimizing defects that typically occur at the buried interface. An outstanding champion efficiency of 24.74% was obtained for the devices, followed by enhanced reproducibility with an average power conversion efficiency (PCE) of 24.13 ± 0.26%, which is notably higher than that (22.73 ± 0.62%) of the pristine MPTCA-based PSCs. More importantly, the composited HTL-based devices without encapsulation demonstrated remarkable stability, with a decrease of less than 10% in the initial efficiency after 500 h of continuous light soaking.

Enhanced Buried Interface Engineering for Efficient Inverted Perovskite Solar Cells Fabricated via Vapor-Solid Reaction

Vapor-deposited inverted perovskite solar cells utilizing self-assembled monolayer (SAM) as hole transport material have gained significant attention for their high efficiencies and compatibility with silicon/perovskite monolithic tandem devices. However, as a small molecule, the SAM layer suffers low thermal tolerance in comparison with other metal oxide or polymers, rendering poor efficiency in solar device with high-temperature (> 160 °C) fabricating procedures. In this study, a dual modification approach involving AlOx and F-doped phenyltrimethylammonium bromide (F-PTABr) layers is introduced to enhance the buried interface. The AlOx dielectric layer improves the interface contact and prevents the upward diffusion of SAM molecules during the vapor-solid reaction at 170 °C, while the F-PTABr layer regulates crystal growth and reduces the interfacial defects. As a result, the AlOx/F-PTABr-treated perovskite film exhibits a homogeneous, pinhole-free morphology with improved crystal quality compared to the control films. This leads to a champion power conversion efficiency of 21.53% for the inverted perovskite solar cells. Moreover, the encapsulated devices maintained 90% of the initial efficiency after 600 h of ageing at 85 °C in air, demonstrating promising potential for silicon/perovskite tandem application.

Reinforcing Coverage of Self-assembled Monomolecular Layers for Inverted Perovskite Solar Cells with Efficiency of 25.70

Self-assembled monolayers (SAM) as hole transport layers have been widely used in high-efficiency inverted perovskite solar cells (PSCs) exceeded 26 %. However, the poor coverage and non-uniform distribution on the substrate of SAM further restrict the improvement of device performance. Herein, we utilize the mixed SAM strategy via the MeO-2PACz along with perfluorotripropylamine (FC-3283) to improve the SAM coverage, aiming to accelerate the carrier transport, promote the perovskite growth, regulate the surface energy levels and suppress the nonradiative recombination. The champion device with the mixed-SAM achieves an efficiency of 25.70 % (certified efficiency of 25.6 %) with long-term stability (maintained the initial efficiency of 90 % after 1000 h and 180 h under ISOS-L-1 and ISOS-L-2).

ALD-Deposited Hydroxyl-Rich NiOx to Enhance SAM Anchoring for Stable and Efficient Perovskite Solar Cells

The interface between nickel oxide (NiOx) and self-assembled monolayers (SAMs) in perovskite solar cells (PSCs) often suffers from limited adsorption strength, poor energy-level alignment, and inadequate defect passivation, which hinder device performance and stability. To address these issues, we introduce a hybrid hole selective layer (HSL) combining atomic layer deposition (ALD)-fabricated NiOx with full-aromatic SAM molecules, creating a highly stable and efficient interface. ALD NiOx, enriched with hydroxyl groups, provides robust adsorption sites for the SAM molecule MeO-PhPACz, ensuring a strong, stable interaction. This hybrid HSL enhances energy-level alignment, hole selectivity, and defect passivation at the NiOx/perovskite interface. Devices utilizing this approach demonstrate significant performance improvements, achieving a power conversion efficiency (PCE) of 21.74%, with reduced voltage losses and minimal hysteresis. Furthermore, operational stability tests reveal enhanced durability under elevated humidity and temperature conditions. These findings highlight the potential of ALD NiOx and SAM hybrid HSL to overcome existing barriers, advancing the commercial viability of PSC technologies.

Enhancing Performance of NiOx-Based Inverted Perovskite Solar Cells: Advances in Buried Interface Material Modification Strategy

Inverted perovskite solar cells (PSCs) have become a current research hotspot due to their advantages such as low-temperature preparation, low hysteresis, and compatibility with stacked other cells. NiOx, as a metal oxide hole transport layer material, is widely used in inverted PSCs. However, challenges such as high defect density, low intrinsic conductivity, and unfavorable valence band mismatch at the NiOx/perovskite interface hinder further improvement of device performance. Therefore, enhancing the buried interface between NiOx and perovskite layers is crucial for optimizing performance. This review systematically categorizes materials based on their types, including organic small molecules, self-assembled monolayers (SAMs), polymers, and salts. Additionally, it incorporates other strategies, such as the introduction of low-dimensional materials, metal doping, and advancements in NiOx deposition technology. By reviewing the materials and technologies used in the past 2 years, this article aims to provide insights for enhancing the buried interface to achieve more efficient and stable NiOx-based PSCs. Finally, we also discuss future directions and challenges.

Enhancing efficiency and stability in perovskite solar cells: innovations in self-assembled monolayers

Perovskite solar cells (PVSCs) show remarkable potential due to their high-power conversion efficiencies and scalability. However, challenges related to stability and long-term performance remain significant. Self-assembled monolayers (SAMs) have emerged as a crucial solution, enhancing interfacial properties, facilitating hole extraction, and minimizing non-radiative recombination. This review examines recent advancements in SAMs for PVSCs, focusing on three key areas: anchoring groups and interface engineering, electronic structure modulation as well as band alignment, and stability optimization. We emphasize the role of anchoring groups in reducing defects and improving crystallinity, alongside the ability of SAMs to fine-tune energy levels for more effective hole extraction. Additionally, co-adsorbed SAM strategies was discussed which can enhance the durability of PVSCs against thermal and moisture degradation. Overall, SAMs present a promising avenue for addressing both efficiency and stability challenges in PVSCs, paving the way toward commercial viability. Future research should prioritize long-term environmental durability and the scaling up of SAM applications for industrial implementation.

Interfacial Dipole Engineering for Energy Level Alignment in NiOx-Based Quantum Dot Light-Emitting Diodes

The solution-derived non-stoichiometric nickel oxide (NiOx) is a promising hole-injecting material for stable quantum dot light-emitting diodes (QLEDs). However, the carrier imbalance due to the misalignment of energy levels between the NiOx and polymeric hole-transporting layers (HTLs) curtails the device efficiency. In this study, the modification of the NiOx surface is investigated using either 3-cyanobenzoic acid (3-CN-BA) or 4-cyanobenzoic acid (4-CN-BA) in the QLED fabrication. Morphological and electrical analyses revealed that both 4-CN-BA and 3-CN-BA can enhance the work function of NiOx, reduce the oxygen vacancies on the NiOx surface, and facilitate a uniform morphology for subsequent HTL layers. Moreover, it is found that the binding configurations of dipole molecules as a function of the substitution position of the tail group significantly impact the work function of underlying layers. When integrated in QLEDs, the modification layers resulted in a significant improvement in the electroluminescent efficiency due to the enhancement of energy level alignment and charge balance within the devices. Specifically, QLEDs incorporating 4-CN-BA achieved a champion external quantum efficiency (EQE) of 20.34%, which is a 1.8X improvement in comparison with that of the devices utilizing unmodified NiOx (7.28%). Moreover, QLEDs with 4-CN-BA and 3-CN-BA modifications exhibited prolonged operational lifetimes, indicating potential for practical applications.

A Polymeric Hole Transporter with Dual-Interfacial Interactions Enables 25%-Efficiency Blade-Coated Perovskite Solar Cells

Self-assembly monolayer (SAM) hole transporters, consisting of anchoring, spacer, and terminal groups, have played a significant role in the development of inverted perovskite solar cells (PSCs). However, the weak interaction between perovskite and hydrophobic terminal group of SAMs limits surface wettability and interface stability. To address this issue, two novel hole transporters (named DBPP and Poly-DBPP) with centrosymmetric biphosphonic acid groups are developed. Unlike conventional SAM hole transporters, the biphosphonic acid groups in DBPP and Poly-DBPP can anchor to the underlying conductive substrate and interact with the perovskite layer simultaneously, improving surface wettability and suppressing interface recombination. Furthermore, compared to the small-molecular DBPP, Poly-DBPP exhibits higher conductance and excellent uniformity. This translates to a remarkable power conversion efficiency of 25.1% for blade-coated PSCs and 22.0% for large-area modules, respectively. Additionally, the PSCs based on Poly-DBPP demonstrate impressive operational stability, retaining 92% of their initial PCE after 1,600 h of light soaking. This work presents a promising strategy for designing multifunctional hole transporters, paving the way for highly efficient and stable PSCs.

Application of PACz-Based Self-Assembled Monolayer Materials in Efficient Perovskite Solar Cells

Due to the advantages of low interface resistance, high work function, and high stability, PACz family materials have developed rapidly in p-i-n structure perovskite solar cells (PSCs) in recent years. Numerous studies have shown that PSCs prepared on the basis of PACz family materials or their derivatives as hole transport layers (HTLs) generally exhibit superior performance compared to PSCs prepared on the basis of organic HTL PTAA and inorganic HTL NiOx, especially in terms of stability, demonstrating unparalleled charm. Since the application of PACz-like molecule V1036 as a HTL in PSCs in 2018, research reports on high-performance PSCs based on the PACz family HTL have been widely disseminated. Currently, PSCs based on the PACz HTL exhibit a world record value of 26.7% power conversion efficiency (PCE), breaking the long-standing world record held by n-i-p-structured PSCs, indicating its great potential for application in PSCs. The main problem with using PACz as a HTL is that it exhibits poor wettability toward perovskite precursor solutions, is sensitive to the thickness of the HTL and the roughness of the substrate, has poor thermal stability, and lacks preparation methods, making it difficult to achieve large-area device fabrication. This review summarizes the outstanding achievements of PACz to date, describes the mechanism and unique properties of PACz in PSCs, and looks forward to the future development prospects of PACz.

Suppressing Hole Accumulation Through Sub-Nanometer Dipole Interfaces in Hybrid Perovskite/Organic Solar Cells for Boosting Near-Infrared Photon Harvesting

The potential of hybrid perovskite/organic solar cells (HSCs) is increasingly recognized owing to their advantageous characteristics, including straightforward fabrication, broad-spectrum photon absorption, and minimal open-circuit voltage (VOC) loss. Nonetheless, a key bottleneck for efficiency improvement is the energy level mismatch at the perovskite/bulk-heterojunction (BHJ) interface, leading to charge accumulation. In this study, it is demonstrated that introducing a uniform sub-nanometer dipole layer formed of B3PyMPM onto the perovskite surface effectively reduces the 0.24 eV energy band offset between the perovskite and the donor of BHJ. This strategic modification suppresses the charge recombination loss, resulting in a noticeable 30 mV increase in the VOC and a balanced carrier transport, accompanied by a 5.0% increase in the fill factor. Consequently, HSCs that achieve power conversion efficiency of 24.0% is developed, a new record for Pb-based HSCs with a remarkable increase in the short-circuit current of 4.9 mA cm-2, attributed to enhanced near-infrared photon harvesting.

On the V OC loss in NiO-based inverted metal halide perovskite solar cells

Recent reports have shown that nickel oxide (NiO) when adopted as a hole transport layer (HTL) in combination with organic layers, such as PTAA or self-assembled monolayers (SAMs), leads to a higher device yield for both single junction as well as tandem devices. Nevertheless, implementing NiO in devices without PTAA or SAM is seldom reported to lead to high-performance devices. In this work, we assess the effect of key NiO properties deemed relevant in literature, namely- resistivity and surface energy, on the device performance and systematically compare the NiO-based devices with those based on PTAA. To this purpose, (thermal) atomic layer deposited (ALD) NiO (NiOBu-MeAMD), Al-doped NiO (Al:NiOBu-MeAMD), and plasma-assisted ALD NiO (NiOMeCp) films, characterized by a wide range of resistivity, are investigated. Although Al:NiOBu-MeAMD (∼400 Ω cm) and NiOMeCp(∼80 Ωcm) films have a lower resistivity than NiOBu-MeAMD (∼10 kΩ cm), the Al:NiOBu-MeAMD and NiOMeCp-based devices are found to have a modest open circuit voltage (V OC) gain of ∼30 mV compared to NiOBu-MeAMD-based devices. Overall, the best-performing NiO-based devices (∼14.8% power conversion efficiency (PCE)) still lag behind the PTAA-based devices (∼17.5%), primarily due to a V OC loss of ∼100 mV. Further investigation based on light intensity analysis of the V OC and FF and the decrease in V OC compared to the quasi-Fermi level splitting (QFLS) indicates that the V OC is limited by trap-assisted recombination at the NiO/perovskite interface. Additionally, SCAPS simulations show that the presence of a high interfacial trap density leads to a V OC loss in NiO-based devices. Upon passivation of the NiO/perovskite interface with Me-4PACz, the V OC increases by 170-200 mV and is similar for NiOBu-MeAMD and Al:NiOBu-MeAMD, leading to the conclusion that there is no influence of the NiO resistivity on the V OC once interface passivation is realized. Finally, our work highlights the necessity of comparing NiO-based devices with state-of-the-art HTL-based devices to draw conclusion about the influence of specific material properties on device performance.

Understanding the Impact of SAM Fermi Levels on High Efficiency p-i-n Perovskite Solar Cells

Completing the picture of the underlying physics of perovskite solar cell interfaces that incorporate self-assembled molecular layers (SAMs) will accelerate further progress in p-i-n devices. In this work, we modified the Fermi level of a nickel oxide-perovskite interface by utilizing SAM layers with a range of dipole strengths to establish the link between the resulting shift of the built-in potential of the solar cell and the device parameters. To achieve this, we fabricated a series of high-efficiency perovskite solar cells with no hysteresis and characterized them through stabilize and pulse (SaP), JV curve, and time-resolved photoluminescence (TRPL) measurements. Our results unambiguously show that the potential drop across the perovskite layer (in the range of 0.6-1 V) exceeds the work function difference at the device's electrodes. These extracted potential drop values directly correlate to work function differences in the adjacent transport layers, thus demonstrating that their Fermi level difference entirely drives the built-in potential in this device configuration. Additionally, we find that selecting a SAM with a deep HOMO level can result in charge accumulation at the interface, leading to reduced current flow. Our findings provide insights into the device physics of p-i-n perovskite solar cells, highlighting the importance of interfacial energetics on device performance.

Development of Lightweight and Flexible Perovskite Solar Cells on Ultrathin Colorless Polyimide Foils

The development of Perovskite Solar Cells (PSCs) on flexible substrates marks a significant advancement in thin-film photovoltaic technology. However, current state-of-the-art research predominantly utilizes Poly(ethylene terephthalate) (PET) substrate, which limits the deployment to less challenging environments. To address this limitation, we explore the fabrication of inverted PSCs on colorless polyimide (CPI) substrates that can withstand harsh environmental conditions. We employed a sequential sputtering technique to deposit indium tin oxide (bottom electrode) and nickel oxide (hole transport layer) as a base stack for the perovskite. This base layer was further enhanced by incorporating MeO-2PACz into the hole transport bilayer, significantly improving the NiOx interface, and thereby enhancing the efficiency of the devices. The PSCs fabricated on CPI demonstrated a power conversion efficiency (PCE) of 15.52% and a remarkable power-to-weight ratio (PWR) of 4.39 W/g, which is five times higher than that of devices on PET (0.87 W/g). Moreover, the active stack developed in this study can be used on any transparent substrate, showing its broader application potential.

Co-adsorbed self-assembled monolayer enables high-performance perovskite and organic solar cells

Self-assembled monolayers (SAMs) have become pivotal in achieving high-performance perovskite solar cells (PSCs) and organic solar cells (OSCs) by significantly minimizing interfacial energy losses. In this study, we propose a co-adsorb (CA) strategy employing a novel small molecule, 2-chloro-5-(trifluoromethyl)isonicotinic acid (PyCA-3F), introducing at the buried interface between 2PACz and the perovskite/organic layers. This approach effectively diminishes 2PACz's aggregation, enhancing surface smoothness and increasing work function for the modified SAM layer, thereby providing a flattened buried interface with a favorable heterointerface for perovskite. The resultant improvements in crystallinity, minimized trap states, and augmented hole extraction and transfer capabilities have propelled power conversion efficiencies (PCEs) beyond 25% in PSCs with a p-i-n structure (certified at 24.68%). OSCs employing the CA strategy achieve remarkable PCEs of 19.51% based on PM1:PTQ10:m-BTP-PhC6 photoactive system. Notably, universal improvements have also been achieved for the other two popular OSC systems. After a 1000-hour maximal power point tracking, the encapsulated PSCs and OSCs retain approximately 90% and 80% of their initial PCEs, respectively. This work introduces a facile, rational, and effective method to enhance the performance of SAMs, realizing efficiency breakthroughs in both PSCs and OSCs with a favorable p-i-n device structure, along with improved operational stability.

Recent Advances in Carbazole-Based Self-Assembled Monolayer for Solution-Processed Optoelectronic Devices

Self-assembled molecules (SAMs) have shown great potential in the application of optoelectronic devices due to their unique molecular properties. Recently, emerging phosphonic acid-based SAMs, 2-(9Hcarbazol-9-yl)ethyl]phosphonic acid (2PACz), have successfully applied in perovskite solar cells (PSCs), organic solar cells (OSCs) and perovskite light emitting diodes (PeLEDs). More importantly, impressive results based on 2PACz SAMs are reported recently in succession. Therefore, it is essential to provide an insightful summary to promote it further development. In this review, the molecule design strategies about 2PACz are first concluded. Subsequently, this work systematically reviews the recent advances of 2PACz and its derivatives for single junction PSCs, tandem PSCs, OSCs and PeLEDs. Finally, this work concludes and discusses future challenges for 2PACz and its derivatives to further develop in optoelectronic devices.

Tuning Hole-Injection in Organic-Light Emitting Diodes with Self-Assembled Monolayers

Improving hole injection through the surface modification of indium tin oxide (ITO) with self-assembled monolayers (SAMs) is a promising method for modulating the carrier injection in organic light-emitting diodes (OLEDs). However, developing SAMs with the required characteristics remains a daunting challenge. Herein, we functionalize ITO with various phosphonic acid SAMs and evaluate the SAM-modified anodes in terms of their work function (WF), molecular distribution, coverage, and electrical conductivity. We fabricate and characterize green phosphorescent SAM-based OLEDs and compared their performance against devices based on the conventional poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) hole-injection layer. We find that the usage of [2-(3,6-diiodo-9H-carbazol-9-yl)ethyl]phosphonic acid (I-2PACz) SAM yields devices with superior performance characteristics, including a maximum luminance of ∼57,300 cd m-2 and external quantum efficiency of up to ∼17%. This improvement is attributed to synergistic factors, including the deep WF of ITO/I-2PACz (5.47 eV), the formation of larger I-2PACz molecular clusters, and the intrinsic I-2PACz dipole, that collectively enhance hole-injection.

Key Roles of Interfaces in Inverted Metal-Halide Perovskite Solar Cells

Metal-halide perovskite solar cells (PSCs), an emerging technology for transforming solar energy into a clean source of electricity, have reached efficiency levels comparable to those of commercial silicon cells. Compared with other types of PSCs, inverted perovskite solar cells (IPSCs) have shown promise with regard to commercialization due to their facile fabrication and excellent optoelectronic properties. The interlayer interfaces play an important role in the performance of perovskite cells, not only affecting charge transfer and transport, but also acting as a barrier against oxygen and moisture permeation. Herein, we describe and summarize the last three years of studies that summarize the advantages of interface engineering-based advances for the commercialization of IPSCs. This review includes a brief introduction of the structure and working principle of IPSCs, and analyzes how interfaces affect the performance of IPSC devices from the perspective of photovoltaic performance and device lifetime. In addition, a comprehensive summary of various interface engineering approaches to solving these problems and challenges in IPSCs, including the use of interlayers, interface modification, defect passivation, and others, is summarized. Moreover, based upon current developments and breakthroughs, fundamental and engineering perspectives on future commercialization pathways are provided for the innovation and design of next-generation IPSCs.

Impact of the TCO Microstructure on the Electronic Properties of Carbazole-Based Self-Assembled Monolayers

Carbazole-based self-assembled monolayers (PACz-SAMs), anchored via their phosphonic acid group on a transparent conductive oxide (TCO), have demonstrated excellent performance as hole-selective layers in perovskite/silicon tandem solar cells. Yet, whereas different PACz-SAMs have been explored, the role of the TCO, and specifically its microstructure, on the hole transport properties of the TCO/PACz-SAMs stack has been largely overlooked. Here, we demonstrate that the TCO microstructure directly impacts the work function (WF) shift after SAM anchoring and is responsible for WF variations at the micro/nanoscale. Specifically, we studied Sn-doped In2O3 (ITO) substrates with amorphous and polycrystalline (featuring either nanoscale- or microscale-sized grains) microstructures before and after 2PACz-SAMs and NiOx/2PACz-SAMs anchoring. With this, we established a direct correlation between the ITO crystal grain orientation and 2PACz-SAMs local potential distribution, i.e., the WF. Importantly, these variations vanish for amorphous oxides (either in the form of amorphous ITO or when adding an amorphous NiOx buffer layer), where a homogeneous surface potential distribution is found. These findings highlight the importance of TCO microstructure tuning, to enable both high mobility and broadband transparent electrodes while ensuring uniform WF distribution upon application of hole transport SAMs, both critical for enhanced device performance.

Understanding the Heterointerfaces in Perovskite Solar Cells via Hole Selective Layer Surface Functionalization

Interfaces in perovskite solar cells (PSCs) play a pivotal role in determining device performance by influencing charge transport and recombination. Understanding the physical processes at these interfaces is essential for achieving high-power conversion efficiency in PSCs. Particularly, the interfaces involving oxide-based transport layers are susceptible to defects like dangling bonds, excess oxygen, or oxygen deficiency. To address this issue, the surface of NiOx is passivated using octadecylphosphonic acid (ODPA), resulting in improved charge transport across the perovskite hole transport layer (HTL) interface. This surface treatment has led to the development of hysteresis-free devices with an impressive ≈13% increase in power conversion efficiency. Computational studies have explored the halide perovskite architecture of ODPA-treated HTL/Perovskite, aiming to unlock superior photovoltaic performance. The ODPA surface functionalization has demonstrated enhanced device performance, characterized by superior charge exchange capacity. Moreover, higher band-to-band recombination in photoluminescence and electroluminescence indicates presence of lower mid-gap energy states, thereby increasing the effective photogenerated carrier density. These findings are expected to promote the utilization of various phosphonic acid-based self-assembly monolayers for surface passivation of oxide-based transport layers in perovskite solar cells. Ultimately, this research contributes to the realization of efficient halide PSCs by harnessing the favorable architecture of NiOx interfaces.

Homogenized NiOx nanoparticles for improved hole transport in inverted perovskite solar cells

The power conversion efficiency (PCE) of inverted perovskite solar cells (PSCs) is still lagging behind that of conventional PSCs, in part because of inefficient carrier transport and poor morphology of hole transport layers (HTLs). We optimized self-assembly of [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) onto nickel oxide (NiOx) nanoparticles as an HTL through treatment with hydrogen peroxide, which created a more uniform dispersion of nanoparticles with high conductivity attributed to the formation of Ni3+ as well as surface hydroxyl groups for bonding. A 25.2% certified PCE for a mask size of 0.074 square centimeters was obtained. This device maintained 85.4% of the initial PCE after 1000 hours of stabilized power output operation under 1 sun light irradiation at about 50°C and 85.1% of the initial PCE after 500 hours of accelerated aging at 85°C. We obtained a PCE of 21.0% for a minimodule with an aperture area of 14.65 square centimeters.

Low-loss contacts on textured substrates for inverted perovskite solar cells

Inverted perovskite solar cells (PSCs) promise enhanced operating stability compared to their normal-structure counterparts1-3. To improve efficiency further, it is crucial to combine effective light management with low interfacial losses4,5. Here we develop a conformal self-assembled monolayer (SAM) as the hole-selective contact on light-managing textured substrates. Molecular dynamics simulations indicate that cluster formation during phosphonic acid adsorption leads to incomplete SAM coverage. We devise a co-adsorbent strategy that disassembles high-order clusters, thus homogenizing the distribution of phosphonic acid molecules, and thereby minimizing interfacial recombination and improving electronic structures. We report a laboratory-measured power conversion efficiency (PCE) of 25.3% and a certified quasi-steady-state PCE of 24.8% for inverted PSCs, with a photocurrent approaching 95% of the Shockley-Queisser maximum. An encapsulated device having a PCE of 24.6% at room temperature retains 95% of its peak performance when stressed at 65 °C and 50% relative humidity following more than 1,000 h of maximum power point tracking under 1 sun illumination. This represents one of the most stable PSCs subjected to accelerated ageing: achieved with a PCE surpassing 24%. The engineering of phosphonic acid adsorption on textured substrates offers a promising avenue for efficient and stable PSCs. It is also anticipated to benefit other optoelectronic devices that require light management.

Electrochemical Activation of Atomic-Layer-Deposited Nickel Oxide for Water Oxidation

NiO-based electrocatalysts, known for their high activity, stability, and low cost in alkaline media, are recognized as promising candidates for the oxygen evolution reaction (OER). In parallel, atomic layer deposition (ALD) is actively researched for its ability to provide precise control over the synthesis of ultrathin electrocatalytic films, including film thickness, conformality, and chemical composition. This study examines how NiO bulk and surface properties affect the electrocatalytic performance for the OER while focusing on the prolonged electrochemical activation process. Two ALD methods, namely, plasma-assisted and thermal ALD, are employed as tools to deposit NiO films. Cyclic voltammetry analysis of ∼10 nm films in 1.0 M KOH solution reveals a multistep electrochemical activation process accompanied by phase transformation and delamination of activated nanostructures. The plasma-assisted ALD NiO film exhibits three times higher current density at 1.8 V vs RHE than its thermal ALD counterpart due to enhanced β-NiOOH formation during activation, thereby improving the OER activity. Additionally, the rougher surface formed during activation enhanced the overall catalytic activity of the films. The goal is to unravel the relationship between material properties and the performance of the resulting OER, specifically focusing on how the design of the material by ALD can lead to the enhancement of its electrocatalytic performance.

Advances in chloride additives for high-efficiency perovskite solar cells: multiple points of view

Chloride (Cl) additives are rather effective in improving the performance of perovskite solar cells (PSCs) through the modulation of crystallization process and surface morphology. After incorporating Cl-containing additives, the optoelectrical properties of perovskite films, such as the electron/hole diffusion length and carrier lifetime, are greatly enhanced. However, only a trace amount of Cl has been identified in the resultant perovskite film, and the mechanism of efficiency improvement induced by Cl remains unclear. In this review, we discuss organic and inorganic Cl additives systematically from the perspective of their solubility, volatility, cation size and chemical groups. In addition, the roles of residual Cl anions and cations are analyzed in detail. Finally, some valuable future perspectives of Cl additives are proposed.

Efficient All-Perovskite Tandem Solar Cells with Low-Optical-Loss Carbazolyl Interconnecting Layers

Combining wide-band gap (WBG) and narrow-band gap (NBG) perovskites with interconnecting layers (ICLs) to construct monolithic all-perovskite tandem solar cell is an effective way to achieve high power conversion efficiency (PCE). However, optical losses from ICLs need to be further reduced to leverage the full potential of all-perovskite tandem solar cells. Here, metal oxide nanocrystal layers anchored with carbazolyl hole-selective-molecules (CHs), which exhibit much lower optical loss, is employed to replace poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT : PSS) as the hole transporting layers (HTLs) in lead-tin (Pb-Sn) perovskite sub-cells and ICLs in all-perovskite tandem solar cells. Optically transparent indium tin oxide nanocrystals (ITO NCs) layers are employed to enhance anchoring of CHs, while a mixture of two CHs is adopted to tune the surface energy-levels of ITO NCs. The optimized mixed Pb-Sn NBG perovskite solar cells demonstrate a high PCE of 23.2 %, with a high short-circuit current density (Jsc ) of 33.5 mA cm-2 . A high PCE of 28.1 % is further obtained in all-perovskite tandem solar cells, with the highest Jsc of 16.7 mA cm-2 to date. Encapsulated tandem solar cells maintain 90 % of their reference point after 500 h of operation at the maximum power point (MPP) under 1-Sun illumination.

Enhanced optoelectronic coupling for perovskite/silicon tandem solar cells

Monolithic perovskite/silicon tandem solar cells are of great appeal as they promise high power conversion efficiencies (PCEs) at affordable cost. In state-of-the-art tandems, the perovskite top cell is electrically coupled to a silicon heterojunction bottom cell by means of a self-assembled monolayer (SAM), anchored on a transparent conductive oxide (TCO), which enables efficient charge transfer between the subcells1-3. Yet reproducible, high-performance tandem solar cells require energetically homogeneous SAM coverage, which remains challenging, especially on textured silicon bottom cells. Here, we resolve this issue by using ultrathin (5-nm) amorphous indium zinc oxide (IZO) as the interconnecting TCO, exploiting its high surface-potential homogeneity resulting from the absence of crystal grains and higher density of SAM anchoring sites when compared with commonly used crystalline TCOs. Combined with optical enhancements through equally thin IZO rear electrodes and improved front contact stacks, an independently certified PCE of 32.5% was obtained, which ranks among the highest for perovskite/silicon tandems. Our ultrathin transparent contact approach reduces indium consumption by approximately 80%, which is of importance to sustainable photovoltaics manufacturing4.

Stabilized hole-selective layer for high-performance inverted p-i-n perovskite solar cells

P-i-n geometry perovskite solar cells (PSCs) offer simplified fabrication, greater amenability to charge extraction layers, and low-temperature processing over n-i-p counterparts. Self-assembled monolayers (SAMs) can enhance the performance of p-i-n PSCs but ultrathin SAMs can be thermally unstable. We report a thermally robust hole-selective layer comprised of nickel oxide (NiOx) nanoparticle film with a surface-anchored (4-(3,11-dimethoxy-7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (MeO-4PADBC) SAM that can improve and stabilize the NiOx/perovskite interface. The energetic alignment and favorable contact and binding between NiOx/MeO-4PADBC and perovskite reduced the voltage deficit of PSCs with various perovskite compositions and led to strong interface toughening effects under thermal stress. The resulting 1.53-electron-volt devices achieved 25.6% certified power conversion efficiency and maintained >90% of their initial efficiency after continuously operating at 65 degrees Celsius for 1200 hours under 1-sun illumination.

Managing Excess Lead Iodide with Functionalized Oxo-Graphene Nanosheets for Stable Perovskite Solar Cells

Stability issues could prevent lead halide perovskite solar cells (PSCs) from commercialization despite it having a comparable power conversion efficiency (PCE) to silicon solar cells. Overcoming drawbacks affecting their long-term stability is gaining incremental importance. Excess lead iodide (PbI2 ) causes perovskite degradation, although it aids in crystal growth and defect passivation. Herein, we synthesized functionalized oxo-graphene nanosheets (Dec-oxoG NSs) to effectively manage the excess PbI2 . Dec-oxoG NSs provide anchoring sites to bind the excess PbI2 and passivate perovskite grain boundaries, thereby reducing charge recombination loss and significantly boosting the extraction of free electrons. The inclusion of Dec-oxoG NSs leads to a PCE of 23.7 % in inverted (p-i-n) PSCs. The devices retain 93.8 % of their initial efficiency after 1,000 hours of tracking at maximum power points under continuous one-sun illumination and exhibit high stability under thermal and ambient conditions.

Advances on the Application of Wide Band-Gap Insulating Materials in Perovskite Solar Cells

In recent years, the development of perovskite solar cells (PSCs) is advancing rapidly with their recorded photoelectric conversion efficiency reaching 25.8%. However, for the commercialization of PSCs, it is also necessary to solve their stability issue. In order to improve the device performance, various additives and interface modification strategies have been proposed. While, in many cases, they can guarantee a significant increase in efficiency, but not ensure improved stability. Therefore, materials that improve the device efficiency and stability simultaneously are urgently needed. Some wide band-gap insulating materials with stable physical and chemical properties are promising alternative materials. In this review, the application of wide band-gap insulating materials in PSCs, including their preparation methods, working roles, and mechanisms are described, which will promote the commercial application of PSCs.

Enhanced Interface Compatibility by Ionic Dendritic Molecules To Achieve Efficient and Stable Perovskite Solar Cells

Poly(3-hexylthiophene) (P3HT) represents a promising hole transport material for emerging perovskite solar cells (PSCs) due to its appealing merits of high thermal stability and appropriate hydrophobicity. Nonetheless, large energy losses at the P3HT/perovskite interface lead to unsatisfied efficiency and stability of the devices. Herein, two ionic dendritic molecules, 3,3'-(2,7-bis(3,6-bis(bis(4-methoxyphenyl)amino)-9H-carbazol-9-yl)-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) iodide and 3,3'-(2,7-bis(bis(4-(bis(4-methoxyphenyl)amino)phenyl)amino)-9H-fluorene-9,9-diyl)bis(N,N,N-trimethylpropan-1-aminium) iodide, namely, MPA-Cz-FAI and MPA-PA-FAI, are rationally designed as the interlayer to enhance interfacial compatibility. The dendritic backbone with conjugated structure endows the hole transport layer with high conductivity, derived from the more ordered microstructure with larger crystallization and higher connectivity of domain zones. Besides, a better energy level alignment is established between P3HT and perovskite, which enhances the charge extraction and transport yield. In addition, the peripheral methoxy groups enable effective defect passivation at the interface to suppress nonradiative recombination and the quaternary ammonium iodide serving as side chains enable efficient interfacial hole extraction contributing to enhanced charge collection yield. As a result, the dopant-free P3HT-based PSCs modified with MPA-Cz-PAI deliver a champion efficiency of 19.7%, significantly higher than that of the control devices (15.4%). More encouragingly, the unencapsulated devices demonstrate competitive environmental stability by retaining over 85% of its initial efficiency after 1500 h of storage under humid conditions (70% relative humidity). This work provides an effective molecular design strategy for interface engineering, envisaging a bright prospect for the further development of efficient and stable perovskite solar cells.

Nanocrystalline Flash Annealed Nickel Oxide for Large Area Perovskite Solar Cells

The industrialization of perovskite solar cells requires adequate materials and processes to make them economically viable and environmentally sustainable. Despite promising results in terms of power conversion efficiency and operational stability, several hole-transport layers currently in use still need to prove their industrial feasibility. This work demonstrates the use of nanocrystalline nickel oxide produced through flash infrared annealing (FIRA), considerably reducing the materials cost, production time, energy, and the amount of solvents required for the hole transport layer. X-ray photoelectron spectroscopy reveals a better conversion to nickel oxide and a higher oxygen-to-nickel ratio for the FIRA films as compared to control annealing methods, resulting in higher device efficiency and operational stability. Planar inverted solar cells produced with triple cation perovskite absorber result in 16.7% power conversion efficiency for 1 cm2 devices, and 15.9% averaged over an area of 17 cm2 .

Buried Interface Dielectric Layer Engineering for Highly Efficient and Stable Inverted Perovskite Solar Cells and Modules

Stability and scalability are essential and urgent requirements for the commercialization of perovskite solar cells (PSCs), which are retarded by the non-ideal interface leading to non-radiative recombination and degradation. Extensive efforts are devoted to reducing the defects at the perovskite surface. However, the effects of the buried interface on the degradation and non-radiative recombination need to be further investigated. Herein, an omnibearing strategy to modify buried and top surfaces of perovskite film to reduce interfacial defects, by incorporating aluminum oxide (Al₂ O₃ ) as a dielectric layer and growth scaffolds (buried surface) and phenethylammonium bromide as a passivation layer (buried and top surfaces), is demonstrated. Consequently, the open-circuit voltage is extensively boosted from 1.02 to 1.14 V with the incorporation of Al₂ O₃ filling the voids between grains, resulting in dense morphology of buried interface and reduced recombination centers. Finally, the impressive efficiencies of 23.1% (0.1 cm² ) and 22.4% (1 cm² ) are achieved with superior stability, which remain 96% (0.1 cm² ) and 89% (1 cm² ) of its initial performance after 1200 (0.1 cm² ) and 2500 h (1 cm² ) illumination, respectively. The dual modification provides a universal method to reduce interfacial defects, revealing a promising prospect in developing high-performance PSCs and modules.

Fully Textured, Production-Line Compatible Monolithic Perovskite/Silicon Tandem Solar Cells Approaching 29% Efficiency

Perovskite/silicon tandem solar cells are promising avenues for achieving high-performance photovoltaics with low costs. However, the highest certified efficiency of perovskite/silicon tandem devices based on economically matured silicon heterojunction technology (SHJ) with fully textured wafer is only 25.2% due to incompatibility between the limitation of fabrication technology which is not compatible with the production-line silicon wafer. Here, a molecular-level nanotechnology is developed by designing NiO_x /2PACz ([2-(9H-carbazol-9-yl) ethyl]phosphonic acid) as an ultrathin hybrid hole transport layer (HTL) above indium tin oxide (ITO) recombination junction, to serve as a vital pivot for achieving a conformal deposition of high-quality perovskite layer on top. The NiO_x interlayer facilitates a uniform self-assembly of 2PACz molecules onto the fully textured surface, thus avoiding direct contact between ITO and perovskite top-cell for a minimal shunt loss. As a result of such interfacial engineering, the fully textured perovskite/silicon tandem cells obtain a certified efficiency of 28.84% on a 1.2-cm² masked area, which is the highest performance to date based on the fully textured, production-line compatible SHJ. This work advances commercially promising photovoltaics with high performance and low costs by adopting a meticulously designed HTL/perovskite interface.

Gas-Assisted Spray Coating of Perovskite Solar Cells Incorporating Sprayed Self-Assembled Monolayers

Self-assembled monolayers (SAMs) are becoming widely utilized as hole-selective layers in high-performance p-i-n architecture perovskite solar cells. Ultrasonic spray coating and airbrush coating are demonstrated here as effective methods to deposit MeO-2PACz; a carbazole-based SAM. Potential dewetting of hybrid perovskite precursor solutions from this layer is overcome using optimized solvent rinsing protocols. The use of air-knife gas-quenching is then explored to rapidly remove the volatile solvent from an MAPbI3 precursor film spray-coated onto an MeO-2PACz SAM, allowing fabrication of p-i-n devices with power conversion efficiencies in excess of 20%, with all other layers thermally evaporated. This combination of deposition techniques is consistent with a rapid, roll-to-roll manufacturing process for the fabrication of large-area solar cells.

Surface Passivation of Sputtered NiO x Using a SAM Interface Layer to Enhance the Performance of Perovskite Solar Cells

Sputtered NiO _x (sp-NiO _x ) is a preferred hole transporting material for perovskite solar cells because of its hole mobility, ease of manufacturability, good stability, and suitable Fermi level for hole extraction. However, uncontrolled defects in sp-NiO _x can limit the efficiency of solar cells fabricated with this hole transporting layer. An interfacial layer has been proposed to modify the sp-NiO _x /perovskite interface, which can contribute to improving the crystallinity of the perovskite film. Herein, a 2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz) self-assembled monolayer was used to modify an sp-NiO _x surface. We found that the MeO-2PACz interlayer improves the quality of the perovskite film due to an enlarged domain size, reduced charge recombination at the sp-NiO _x /perovskite interface, and passivation of the defects in sp-NiO _x surfaces. In addition, the band tail states are also reduced, as indicated by photothermal deflection spectroscopy, which thus indicates a reduction in defect levels. The overall outcome is an improvement in the device efficiency from 11.9% to 17.2% due to the modified sp-NiO _x /perovskite interface, with an active area of 1 cm² (certified efficiency of 16.25%). On the basis of these results, the interfacial engineering of the electronic properties of sp-NiO _x /MeO-2PACz/perovskite is discussed in relation to the improved device performance.

All-vacuum deposited perovskite solar cells with glycine modified NiO x hole-transport layers

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted enormous research attention due to their high efficiency and low cost. However, most of the PSCs with high efficiencies still need expensive organic materials as their hole-transport layer (HTL). Obviously, the highly expensive materials go against the low-cost concept of advanced PSCs. In this regard, inorganic NiO _x was considered as an idea HTL due to its good transmittance in the visible region and outstanding chemical stability. But for most of the PSCs with a NiO _x HTL, the hole-extraction efficiency was limited by the unmatched valence band and too many surface defects of the NiO _x layer, especially for the vacuum-deposited NiO _x and perovskite. Herein, we developed a facile strategy to overcome this issue by using self-assembled glycine molecules to treat the NiO _x surface. With glycine on the surface, the NiO _x exhibited a deeper valence band maximum and a faster charge-extraction at the NiO _x /perovskite interface. What's more, the vacuum-deposited perovskite showed a better crystallinity on the NiO _x + glycine substrate. As a result, the PSCs with a glycine interfacial layer achieved a champion PCE of 17.96% with negligible hysteresis. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cells.