Review of Interface Passivation of Perovskite Layer

Influence of Adjustable CeO2 Morphology on the Performance of Ambient Hole Transport Layer-Free Carbon-Based Perovskite Solar Cells

The combined effect of TiO2 and CeO2 as the electron transport layer (ETL) in the hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) to enhance performance characteristics is a less explored research area. In this context, we investigated the effect of morphology-tuned CeO2 in combination with TiO2 in the C-PSCs. Considering the light scattering effect in C-PSCs and the property of extending the light-traveling distance across the photoelectrode, we synthesized rod and cubic CeO2 nanostructures. The synthesized nanoparticles were used over the TiO2 layer, and their photovoltaic performance was compared to that of the TiO2-only C-PSC and analyzed by using impedance and quantum efficiency studies. The light-scattering effect on the C-PSCs, investigated with the diffused reflectance study, found that the rod structure of CeO2 provides better light travel toward the photosensitizer, and the highest power conversion efficiency (PCE) of nearly 12.5% was recorded for the rod-shaped CeO2 in the HTL-free C-PSC, which is 24% higher compared to a pristine TiO2-based C-PSC. Moreover, the devices with rod-shaped CeO2 demonstrated suitable charge transport properties along the perovskite layer and a lower charge recombination rate when compared with the cube structure. This work demonstrates a major breakthrough in the performance enhancement of HTL-free C-PSCs by nanomaterial morphology alteration and fabrication engineering, which can significantly influence future research.

Organic Salt-Doped Polymer Alloy: A New Prototype Hole Transporter for High-Photovoltaic-Performance Perovskite Solar Cells

Hole-transporting layer (HTL) is one of the key components in a regular perovskite solar cell (r-PSC), which has the function of extracting the photon-excited holes from the absorber and then transporting them to the electrode. The most commonly used HTL in r-PSC is LiTFSI and tBP-doped spiro-OMeTAD. The inevitable instability induced by a deliquescent inorganic salt (LiTFSI), the migration of small lithium ions, and the necessary oxidation process in air hinder the commercialization of this technology. In this paper, a new undoped D-A copolymer (P15) is used as a hole-transporting material (HTM) for r-PSC but with moderate photovoltaic performance. Therefore, an organic salt, DPI-TPFB, having a big organic cation and a hydrophobic anion, was used as a dopant to increase the conductivity/hole mobility of P15 while avoiding the instability caused by lithium salt and moisture. Furthermore, an amphiphilic polymer, PDTON (with hole- transporting and perovskite-passivation ability), was added to P15 to form a polymer alloy, (P15 + PDTON), to further enhance the crystallinity and, therefore, the conductivity/hole mobility of P15 via space-confined interaction. As a result, r-PSCs based on DPI-TPFB-doped (P15 + PDTON) HTLs exhibit the highest power conversion efficiency (PCE) of 18.8%, which is higher than those of the cells based on DPI-TPFB-doped P15 (15.08%), DPI-TPFB-doped PDTON (7.37%), and undoped (P15 + PDTON) (15.66%) HTLs. Cells based on DPI-TPFB-doped (P15 + PDTON) HTL also have much better long-term stability than those using LiTFSI and tBP-doped spiro-OMeTAD as an HTL. The studies show that a polymer-compatible organic salt, DPI-TPFB, can be used as a stable dopant to increase the hole mobility of polymeric HTL without sacrificing the stability of the resulting cells, and mixing two ordinary photovoltaic performance polymeric HTLs (such as P15 and PDTON) can form a high- photovoltaic-performance polymer alloy (P15 + PDTON) HTL. Therefore, organic salt-doped polymer alloy can be regarded as a new prototype hole transporter for high-photovoltaic- performance PSCs.

Optoelectric coordinated modulation of resistive switching behavior in perovskite based synaptic device

Triple cation halide perovskite (TCP) stands out as a superior photoelectric material, with a broader absorption range, higher absorption efficiency, and improved environmental stability. Due to its excellent synaptic plasticity, TCP facilitates advanced neural morphological operations like light-assisted learning. Here, a modifying layer of polythiophene (P3HT) was incorporated onto the TCP thin film to enhance the resistive switching (RS) characteristics of the synaptic device, which exhibits excellent stability (103 endurance cycles and > 103 s retention time) and low energy consumption (~ 6.3 pJ for electrical stimulus and ~ 6 pJ for optical stimulus). Additionally, the synaptic properties of the perovskite / P3HT heterojunction synaptic device were explored under optoelectric coordinated modulation, encompassing Long-Term Potentiation (LTP), Long-Term Depression (LTD), frequency-dependent plasticity (SRDP) and voltage-dependent plasticity (SVDP). By leveraging the linear characteristics of synaptic plasticity, arithmetic operations, Pavlovian conditioned reflex and vision recognition are achieved. The recognition accuracies of 89.8% / 88.1% (electric synapse) are enhanced to 92.4% / 92.2% after the introduction of optoelectronic cooperative stimulation on the 8 × 8 and 28 × 28 modified national institute of standards and technology (MNIST) handwritten digit datasets. This study holds significant implications for guiding the optoelectronic co-regulation of perovskite synaptic devices in the field of synaptic electronics.

The dawn of MXene duo: revolutionizing perovskite solar cells with MXenes through computational and experimental methods

Integrating MXene into perovskite solar cells (PSCs) has heralded a new era of efficient and stable photovoltaic devices owing to their supreme electrical conductivity, excellent carrier mobility, adjustable surface functional groups, excellent transparency and superior mechanical properties. This review provides a comprehensive overview of the experimental and computational techniques employed in the synthesis, characterization, coating techniques and performance optimization of MXene additive in electrodes, hole transport layer (HTL), electron transport layer (ETL) and perovskite photoactive layer of the perovskite solar cells (PSCs). Experimentally, the synthesis of MXene involves various methods, such as selective etching of MAX phases and subsequent delamination. At the same time, characterization techniques encompass X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, which elucidate the structural and chemical properties of MXene. Experimental strategies for fabricating PSCs involving MXene include interfacial engineering, charge transport enhancement, and stability improvement. On the computational front, density functional theory calculations, drift-diffusion modelling, and finite element analysis are utilized to understand MXene's electronic structure, its interface with perovskite, and the transport mechanisms within the devices. This review serves as a roadmap for researchers to leverage a diverse array of experimental and computational methods in harnessing the potential of MXene for advanced PSCs.

Element Regulation and Dimensional Engineering Co-Optimization of Perovskite Memristors for Synaptic Plasticity Applications

Capitalizing on rapid carrier migration characteristics and outstanding photoelectric conversion performance, halide perovskite memristors demonstrate an exceptional resistive switching performance. However, they have consistently faced constraints due to material stability issues. This study systematically employs elemental modulation and dimension engineering to effectively control perovskite memristors with different dimensions and A-site elements. Compared to pure 3D and 2D perovskites, the quasi-2D perovskite memristor, specifically BA0.15MA0.85PbI3, is identified as the optimal choice through observations of resistive switching (HRS current < 10-5 A, ON/OFF ratio > 103, endurance cycles > 1000, and retention time > 104 s) and synaptic plasticity characteristics. Subsequently, a comprehensive investigation into various synaptic plasticity aspects, including paired-pulse facilitation (PPF), spike-variability-dependent plasticity (SVDP), spike-rate-dependent plasticity (SRDP), and spike-timing-dependent plasticity (STDP), is conducted. Practical applications, such as memory-forgetting-memory and recognition of the Modified National Institute of Standards and Technology (MNIST) database handwritten data set (accuracy rate reaching 94.8%), are explored and successfully realized. This article provides good theoretical guidance for synaptic-like simulation in perovskite memristors.

Lead-Free Halide Double Perovskite for High-Performance Photodetectors: Progress and Perspective

Lead halide perovskite has become a promising candidate for high-performance photodetectors (PDs) due to its attractive optical and electrical properties, such as high optical absorption coefficient, high carrier mobility, and long carrier diffusion length. However, the presence of highly toxic lead in these devices has limited their practical applications and even hindered their progress toward commercialization. Therefore, the scientific community has been committed to searching for low-toxic and stable perovskite-type alternative materials. Lead-free double perovskite, which is still in the preliminary stage of exploration, has achieved inspiring results in recent years. In this review, we mainly focus on two types of lead-free double perovskite based on different Pb substitution strategies, including A₂M(I)M(III)X₆ and A₂M(IV)X₆. We review the research progress and prospects of lead-free double perovskite photodetectors in the past three years. More importantly, from the perspective of optimizing the inherent defects in materials and improving device performance, we propose some feasible pathways and make an encouraging perspective for the future development of lead-free double perovskite photodetectors.

Chemical approaches for electronic doping in photovoltaic materials beyond crystalline silicon

Electronic doping is applied to tailor the electrical and optoelectronic properties of semiconductors, which have been widely adopted in information and clean energy technologies, like integrated circuit fabrication and PVs. Though this concept has prevailed in conventional PVs, it has achieved limited success in the new-generation PV materials, particularly in halide perovskites, owing to their soft lattice nature and self-compensation by intrinsic defects. In this review, we summarize the evolution of the theoretical understanding and strategies of electronic doping from Si-based photovoltaics to thin-film technologies, e.g., GaAs, CdTe and Cu(In,Ga)Se₂, and also cover the emerging PVs including halide perovskites and organic solar cells. We focus on the chemical approaches to electronic doping, emphasizing various chemical interactions/bonding throughout materials synthesis/modification to device fabrication/operation. Furthermore, we propose new classifications and models of electronic doping based on the physical and chemical properties of dopants, in the context of solid-state chemistry, which inspires further development of optoelectronics based on perovskites and other hybrid materials. Finally, we outline the effects of electronic doping in semiconducting materials and highlight the challenges that need to be overcome for reliable and controllable doping.

Simultaneous Optimization of Charge Transport Properties in a Triple-Cation Perovskite Layer and Triple-Cation Perovskite/Spiro-OMeTAD Interface by Dual Passivation

Molecular engineering of additives is a highly effective method to increase the efficiency of perovskite solar cells by reducing trap states and charge carrier barriers in bulk and on the thin film surface. In particular, the elimination of undercoordinated lead species that act as the nonradiative charge recombination center or contain defects that may limit interfacial charge transfer is critical for producing a highly efficient triple-cation perovskite solar cell. Here, 2-iodoacetamide (2I-Ac), 2-bromoacetamide (2Br-Ac), and 2-chloroacetamide (2Cl-Ac) molecules, which can be coordinated with lead, have been used by adding them into a chlorobenzene antisolvent to eliminate the defects encountered in the triple-cation perovskite thin film. The passivation process has been carried out with the coordination between the oxygen anion (-) and the lead (+2) cation on the enolate molecule, which is in the resonance structure of the molecules. The Spiro-OMeTAD/triple-cation perovskite interface has been improved by surface passivation by releasing HX (X = I, Br) as a byproduct because of the separation of alpha hydrogen on the molecule. As a result, a solar cell with a negligible hysteresis operating at 19.5% efficiency has been produced by using the 2Br-Ac molecule, compared to the 17.6% efficiency of the reference cell.

Semitransparent Perovskite Solar Cells with > 13% Efficiency and 27% Transperancy Using Plasmonic Au Nanorods

Semitransparent hybrid perovskites open up applications in windows and building-integrated photovoltaics. One way to achieve semitransparency is by thinning the perovskite film, which has several benefits such as cost efficiency and reduction of lead. However, this will result in a reduced light absorbance; therefore, to compromise this loss, it is possible to incorporate plasmonic metal nanostructures, which can trap incident light and locally amplify the electromagnetic field around the resonance peaks. Here, Au nanorods (NRs), which are not detrimental for the perovskite and whose resonance peak overlaps with the perovskite band gap, are deposited on top of a thin (∼200 nm) semitransparent perovskite film. These semitransparent perovskite solar cells with 27% average visible transparency show enhancement in the open-circuit voltage (V_oc) and fill factor, demonstrating 13.7% efficiency (improved by ∼6% compared to reference cells). Space-charge limited current, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses shed more light on the trap density, nonradiative recombination, and defect density in these Au NR post-treated semitransparent perovskite solar cells. Furthermore, Au NR implementation enhances the stability of the solar cell under ambient conditions. These findings show the ability to compensate for the light harvesting of semitransparent perovskites using the plasmonic effect.

Colloidal Metal-Halide Perovskite Nanoplatelets: Thickness-Controlled Synthesis, Properties, and Application in Light-Emitting Diodes

Colloidal metal-halide perovskite nanocrystals (MHP NCs) are gaining significant attention for a wide range of optoelectronics applications owing to their exciting properties, such as defect tolerance, near-unity photoluminescence quantum yield, and tunable emission across the entire visible wavelength range. Although the optical properties of MHP NCs are easily tunable through their halide composition, they suffer from light-induced halide phase segregation that limits their use in devices. However, MHPs can be synthesized in the form of colloidal nanoplatelets (NPls) with monolayer (ML)-level thickness control, exhibiting strong quantum confinement effects, and thus enabling tunable emission across the entire visible wavelength range by controlling the thickness of bromide or iodide-based lead-halide perovskite NPls. In addition, the NPls exhibit narrow emission peaks, have high exciton binding energies, and a higher fraction of radiative recombination compared to their bulk counterparts, making them ideal candidates for applications in light-emitting diodes (LEDs). This review discusses the state-of-the-art in colloidal MHP NPls: synthetic routes, thickness-controlled synthesis of both organic-inorganic hybrid and all-inorganic MHP NPls, their linear and nonlinear optical properties (including charge-carrier dynamics), and their performance in LEDs. Furthermore, the challenges associated with their thickness-controlled synthesis, environmental and thermal stability, and their application in making efficient LEDs are discussed.

A Brief Review of the Role of 2D Mxene Nanosheets toward Solar Cells Efficiency Improvement

This article discusses the application of two-dimensional metal MXenes in solar cells (SCs), which has attracted a lot of interest due to their outstanding transparency, metallic electrical conductivity, and mechanical characteristics. In addition, some application examples of MXenes as an electrode, additive, and electron/hole transport layer in perovskite solar cells are described individually, with essential research issues highlighted. Firstly, it is imperative to comprehend the conversion efficiency of solar cells and the difficulties of effectively incorporating metal MXenes into the building blocks of solar cells to improve stability and operational performance. Based on the analysis of new articles, several ideas have been generated to advance the exploration of the potential of MXene in SCs. In addition, research into other relevant MXene suitable in perovskite solar cells (PSCs) is required to enhance the relevant work. Therefore, we identify new perspectives to achieve solar cell power conversion efficiency with an excellent quality-cost ratio.

Application of MXenes in Perovskite Solar Cells: A Short Review

Application of MXene materials in perovskite solar cells (PSCs) has attracted considerable attention owing to their supreme electrical conductivity, excellent carrier mobility, adjustable surface functional groups, excellent transparency and superior mechanical properties. This article reviews the progress made so far in using Ti3C2Tx MXene materials in the building blocks of perovskite solar cells such as electrodes, hole transport layer (HTL), electron transport layer (ETL) and perovskite photoactive layer. Moreover, we provide an outlook on the exciting opportunities this recently developed field offers, and the challenges faced in effectively incorporating MXene materials in the building blocks of PSCs for better operational stability and enhanced performance.