Perovskite Photoluminescence Research Articles

Toward efficient and industrially compatible fully textured perovskite silicon tandem solar cells: Controlled process parameters for reliable perovskite formation

AbstractCapitalizing on the existing silicon industry, fully textured perovskite‐silicon tandem solar cells have a great potential to penetrate the electricity market. While the use of textured silicon with large pyramid size (> 1 μm) enhances the power conversion efficiency (PCE), it also presents process complications. To achieve high performance, meticulous control of deposition parameters on textured silicon is required. This study provides a guideline for the use of the hybrid evaporation/spin‐coating route to form high‐quality perovskite absorbers. Using various characterization techniques, we highlight intrinsic differences between perovskite growth on flat versus textured substrates. Furthermore, we provide pathways to ensure a high perovskite phase purity, reveal mitigation strategies to avoid the formation of undesired dendritic perovskite structures, give guidelines to ensure photostability, and discuss the “misleading” effect of residual PbI2 on the perovskite photoluminescence response. A good understanding of the perovskite growth on textured silicon enables the fabrication of a tandem device with a PCE > 26% (without employing additives or surface treatments) and a good operational stability. The comprehensive guidelines in this study provide a better understanding of perovskite formation on textured silicon and can be transferred when upscaling the hybrid route perovskite deposition.

(Invited) Plasma Processes on Metal Halide Perovskite Interfaces for Photovoltaic Applications

Metal Halide Perovskite (MHP) semiconductors are currently standing out for their exceptional optoelectronic properties and, particularly, for their exploitation in photovoltaics. Their structure can be described by the formula , where A is usually an organic cation, such as methylammonium (MA) or formamidinium (FA), B is a metal cation and X is a halogen anion, typically I or Br.The exceptional properties of MHPs derive by their hybrid organic-inorganic nature, which also allows for low-cost fabrication processing. The raise of perovskite photovoltaics 1 followed progresses on three main research fronts: i) material deposition optimization, ii) material compositional tuning and iii) device interface engineering. The interfaces play a fundamental role in the device function affecting charge extraction, recombination processes and material/device overall stability. Therefore, to further improve the performances of these devices, many surface processes have been applied to solar cells interfaces, most of which include a solution-based methodology 2. The aim of these treatments is not only to improve solar cells efficiency in terms of carrier concentration and transport properties, but also to improve the device stability under working conditions, which is one of the main issues of these materials.Among the different surface treatments exploitable, the use of plasma represents a solvent-free and non-invasive promising strategy to boost MHP solar cells performances. Plasma-deposited coatings on perovskite, as fluorocarbon polymers, have shown to improve material resistance to humidity and photoluminescence properties 3.We have explored the effect of low-pressure plasmas fed with different gases, namely Ar, , and , on Metylammonium Lead Iodide surface4. An interesting improvement of perovskite photoluminescence and solar cell efficiency was observed for Ar and plasma treatments, ascribable both to the removal of organic components, proven to be beneficial to device performances 5, and to other chemical and morphological modifications depending on the gas used. Starting from these results, new plasma surface treatments, plasma-assisted deposition and encapsulation processes will be object of study of future research, to achieve a more complete understanding of the interfacial defects and charge carrier dynamics and to further minimize performance losses and instability issues. References NREL Best Research-Cell Efficiency Chart. https://www.nrel.gov/pv/cell-efficiency.html Han TH, Tan S, Xue J, Meng L, Lee JW, Yang Y. Interface and Defect Engineering for Metal Halide Perovskite Optoelectronic Devices. Advanced Materials. 2019;31(47). doi:10.1002/adma.201803515 Armenise V, Colella S, Milella A, Palumbo F, Fracassi F, Listorti A. Plasma-Deposited Fluorocarbon Coatings on Methylammonium Lead Iodide Perovskite Films. Energies (Basel). 2022;15(13):4512. doi:10.3390/en15134512 Andrea Listorti, Sara Covella, Alberto Perrotta, et al. A study on plasma-assisted modifications of Methylammonium Lead Iodide Perovskite surfaces for photovoltaic applications. Xiao X, Bao C, Fang Y, et al. Argon Plasma Treatment to Tune Perovskite Surface Composition for High Efficiency Solar Cells and Fast Photodetectors. Advanced Materials. 2018;30(9):1-7. doi:10.1002/adma.201705176 Figure 1

Interfacial Topochemical Fluoridation of MAPbI3 by Fluoropolymers

Herein it is demonstrated that, under conditions relevant to perovskite synthesis (>140 °C in air), fluoride can topochemically react across the interface between a halide perovskite and a fluoropolymer when in close contact, thereby creating a small quantity of strongly bonded lead fluoride species. The quantity increases with temperature and processing duration. Photoinduced charge carrier lifetime provides a metric for the resulting changes in electronic structure of the perovskite. Under short-duration and/or moderate temperature processing, fluoride transfer to the perovskite yields increased carrier lifetimes, up to 3-fold longer than control samples, which is attributed to passivation of surface defects. Under more forcing conditions, the trend reverses: excessive fluoridation leads to shortened carrier lifetimes, which is ascribed to substantial interfacial formation of PbF2. It is demonstrated that an interface with bulk crystalline PbF2 quenches perovskite photoluminescence, likely due to PbF2 serving as an electron acceptor for the conduction band of MAPbI3.

Precise Tuning of Multiple Perovskite Photoluminescence by Volume-Controlled Printing of Perovskite Precursor Solution on Cellulose Paper.

Metal halide perovskite nanocrystals (PeNCs) with a controlled quantum size effect have received intense interest for potential applications in optoelectronics and photonics. Here, we present a simple and innovative strategy to precisely tune the photoluminescence color of PeNCs by simply printing perovskite precursor solutions on cellulose papers. Depending on the volume of the printed precursor solutions, the PeNCs are autonomously grown into three discrete sizes, and their relative size population is controlled; accordingly, not only the number of multiple PL peaks but also their relative intensities can be precisely tuned. This autonomous size control is obtained through the efflorescence, which is advection of salt ions toward the surface of a porous medium during solvent evaporation and also through the confined crystal growth in the hierarchical structure of cellulose fibers. The infiltrated PeNCs are environmentally stable against moisture (for 3 months in air at 70% relative humidity) and strong light exposure by hydrophobic surface treatment. This study also demonstrates invisible encryption and highly secured unclonable anticounterfeiting patterns on deformable cellulose substrates and banknotes.

The roles of surface defects in MAPbBr3 and multi-structures in MAPbI3

The research of perovskites optical properties is of great value for dual wavelength lasers. However, the phenomenon of double peaks in perovskites photoluminescence (PL) has not been explained systematically, which makes the optical research of perovskites still a challenge. In order to have a deep understanding of the optical properties and applications of new perovskite materials, this phenomenon of MAPbX3 (X = I−, Br−) is explained in this paper. The structural characteristics of the materials were investigated by XRD. We found that there were PbBr2 defects in MAPbBr3 and orthorhombic structure defects in MAPbI3; By calculating the energy level distribution of perovskites and defects, the PbBr2 in MAPbBr3 and orthorhombic phase structure in MAPbI3 can introduce a new energy level into crystals and these two structures lead to the PL peaks of 542 nm and 771 nm, respectively. It is the surface defects in MAPbBr3 and multi-structures in MAPbI3 that leads to the two peaks phenomenon of perovskite photoluminescence. All the work explained the mechanism of perovskites PL double peaks. This study can provide theoretical reference for perovskites researches and experimental references for new materials and a promising pathway for dual-wavelength, practical laser based on perovskite crystals.

First Conventional Solution Sol–Gel-Prepared Nanoporous Materials of Nickel Oxide for Efficiency Enhancing and Stability Extending MAPbI3 Inverted Perovskite Solar Cells

With a judicious selection of the nickel complex (precursor) and stabilizer, that is, nickel formate and enthylenediamine, respectively, a conventional sol–gel method followed by a sintering process at 450 °C, nanoporous NiOx (np-NiOx) thin films have been successfully prepared. However, the alcohol solvent used in the sol–gel process is critical that only low-viscosity ones, such as methanol, ethanol, 2-methoxyethanol, and iso-propanol, afford np-NiOx instead of plate/flake-like compact NiOx (cp-NiOx). Some stabilizers, such as 1,3-diaminopropane, diethylenetriamine, and N,N-dimethylethylenediamine, provide nothing but seemly amorphous NiOx fragmentary thin films, which are unsuitable for the hole-transporting material (HTM) in the inverted perovskite solar cells (PVSCs). SEM or AFM study has a clear differentiation between np-NiOx and cp-NiOx. Moreover, we have characterized that the np-NiOx thin films show a better conductivity, a higher hole mobility, a stronger perovskite photoluminescence quenching, and a superior transparency than those of cp-NiOx thin films. Using MAPbI3, inverted PVSCs were fabricated with either np-NiOx or cp-NiOx as HTM. A high power conversion efficiency approaching 20% was achieved by np-NiOx-based PVSCs, which was better than our best PVSC (17.95%) based on cp-NiOx. Electrochemical impedance spectroscopy (EIS) has observed a lower charge recombination resistance but a higher charge transport resistance for the cp-NiOx device comparing with those of each np-NiOx devices. Moreover, np-NiOx MAPbI3 PVSCs exhibit a less hysteresis effect and an extended lifetime in terms of shelf stability compared with those of cp-NiOx MAPbI3 PVSCs. The SEM and XRD have demonstrated the larger grain size and less gain boundary of MAPbI3 thin films on np-NiOx HTM, where MAPbI3 is in fact more hydrophobic, evident by the water contact angle.

Efficiency of bulk perovskite-sensitized upconversion: Illuminating matters

Photon upconversion via triplet–triplet annihilation could allow for the existing efficiency limit of single junction solar cells to be surpassed. Indeed, efficient upconversion at subsolar fluences has been realized in bulk perovskite-sensitized systems. Many questions have remained unanswered, in particular, regarding their behavior under photovoltaic operating conditions. Here, we investigate the impact of repeated and continuous illumination on bilayer perovskite/rubrene upconversion devices. We find that variations of the underlying perovskite carrier recombination dynamics greatly impact the upconversion process. Trap filling and triplet sensitization are in direct competition: more saturated trap states in the perovskite and, thus, longer underlying perovskite photoluminescence lifetimes allow for an increased number of carriers to diffuse to the perovskite/rubrene interface and undergo charge extraction to the triplet state of rubrene. As a result, the upconversion efficiency is greatly influenced by the underlying trap density: the upconverted photoluminescence intensity increases by two orders of magnitude under continuous illumination for 4 h. This shows that the upconversion efficiency is difficult to define for this system. Importantly, these results indicate that perovskite-sensitized upconversion devices exhibit peak performance under continuous illumination, which is a requirement for their successful integration into photovoltaics to help overcome the Shockley–Queisser limit in single junction solar cells.

Role of Photon Recycling and Band Filling in Halide Perovskite Photoluminescence under Focussed Excitation Conditions

We study the temporal, spatial, and spectral evolution of charge carriers in hybrid perovskite thin films after optical excitation with a small laser spot. These are conditions typical of microscop...

Underestimated effect of the polymer encapsulation process on the photoluminescence of perovskite revealed by in situ single-particle detection.

Photostability has always been an important issue that limits the performance of organo-metal halide perovskites in optoelectronic devices. Although the photostability can be partially improved by polymer coating/encapsulation, one rising question that needs to be considered is whether the improvement of photostability is accessed at the expense of intangible loss in photoluminescence (PL) properties. By in situ analyzing the evolution of PL properties of individual perovskite crystals during the polymer encapsulation procedure, we demonstrate here that poly(methyl methacrylate), a common polymeric encapsulant, would passivate the surface defects of perovskite crystals, leading to the suppress of PL blinking. However, somewhat counterintuitive, the toluene solvent will induce the PL decline of individual perovskite crystals via accumulation of the number of quenchers that, most probably, are related to the ion migration in perovskite. The findings at the single-particle level emphasize the often-neglected role of the polymer matrix and the solvent in the optical properties of perovskite material during the polymer encapsulation process, and will guide the further design of more stable and high-performance devices based on perovskite.

Impact of Mesoporous Silicon Template Pore Dimension and Surface Chemistry on Methylammonium Lead Trihalide Perovskite Photophysics

AbstractIn influencing fundamental properties—and ultimately device performance—of lead halide perovskites, interfacial interactions play a major role, notably with regard to carrier diffusion and recombination. Here anodized porous Si (pSi) as well as porous silica particles are employed as templates for formation of methylammonium lead trihalide nanostructures. This allows synthesis of relatively small perovskite domains and comparison of associated interfacial chemistry between as‐prepared hydrophobic hydrideterminated functionalities and hydrophilic oxide‐terminated surfaces. While physical confinement of MAPbBr3 has a uniform effect on carrier lifetime, pore size (7–18 nm) of the silicon‐containing template has a sensitive influence on perovskite photoluminescence (PL) wavelength maximum. Furthermore, identity of the surface functionality of the template significantly alters the PL quantum efficiency, with lowest PL intensity associated with the H‐terminated pSi and the most intense PL affiliated with the oxideterminated pSi surface. These effects are explored for green‐emitting MAPbBr3 as well as infrared‐emitting MAPbI3. In addition, the role of silicon surface chemistry on the time‐dependent stability of these perovskites packaged within a given mesoporous template is also evaluated, specifically, a lack of miscibility between MAPbI3 and the H‐terminated pSi template results in a diffusion of this specific perovskite composition eluting from this porous matrix over time.

Enhancement of perovskite photoluminescence characterizations by using lithography-free metal nanostructures

To date, organic–inorganic metal halide perovskite material has become an emerging research topic for scientists to alternate the semiconductor material in the optoelectronic applications. However, the photoluminescence (PL) efficiency of perovskite material is quite low, which impacts the performance of perovskite-based optoelectronic devices. Here, we propose and demonstrate an effective approach to enhance the PL efficiency of perovskite material. We utilize the metal nanostructures fabricated on the perovskite surface. Metal nanostructures possess extraordinary electromagnetic properties, e.g., easily controlled the amplitude, phase, and polarization of the incident light, which can be utilized to enhance the PL performance of the perovskite material. The intensity and spectral bandwidth of the PL spectrum could be enhanced significantly via metal nanostructures. The full width at half maximum of PL spectral bandwidth could be narrowed to several nanometers. This nanostructure-enhanced PL characterization of the perovskite material exhibits better monochromaticity and provides the simple, cost-effective, and potentially scalable method for the development of high-efficiency light emitting diodes, solar cells, photodetectors, etc.

Single-Particle Organolead Halide Perovskite Photoluminescence as a Probe for Surface Reaction Kinetics.

Photoluminescence (PL) of organolead halide perovskites (OHPs) is sensitive to OHPs' surface conditions and is an effective way to report surface states. Literature has reported that at the ensemble level, the PL of photoexcited OHP nanorods declines under an inert nitrogen (N2) atmosphere and recovers under subsequent exposure to oxygen (O2). At the single-particle level, we observed that OHP nanorods photoblink at rates dependent on both the excitation intensity and the O2 concentration. Combining the two sets of information with the charge-trapping/detrapping mechanism, we are able to quantitatively evaluate the interaction between a single surface defect and a single O2 molecule using a new kinetic model. The model predicts that the photodarkening of OHP nanorods in the N2 atmosphere has a different mechanism than conventional PL quenching, which we call photo-knockout. This model provides fundamental insights into the interactions of molecular O2 with OHP materials and helps design a suitable OHP interface for a variety of applications in photovoltaics and optoelectronics.

Identifying an Optimum Perovskite Solar Cell Structure by Kinetic Analysis: Planar, Mesoporous Based, or Extremely Thin Absorber Structure

Perovskite solar cells have rapidly been developed over the past several years. Choice of the most suitable solar cell structure is crucial to improve the performance further. Here, we attempt to determine an optimum cell structure for methylammonium lead iodide (MAPbI3) perovskite sandwiched by TiO2 and spiro-OMeTAD layers, among planar heterojunction, mesoporous structure, and extremely thin absorber structure, by identifying and comparing charge carrier diffusion coefficients of the perovskite layer, interfacial charge transfer, and recombination rates using transient emission and absorption spectroscopies. An interfacial electron transfer from MAPbI3 to compact TiO2 occurs with a time constant of 160 ns, slower than the perovskite photoluminescence (PL) lifetime (34 ns). In contrast, fast non-exponential electron injection to mesoporous TiO2 was observed with at least two different electron injection processes over different time scales; one (60–70%) occurs within an instrument response time of 1.2 ns...

Engineering the Emission of Broadband 2D Perovskites by Polymer Distributed Bragg Reflectors

Thanks to their broadband emission and solution processability, 2D hybrid perovskite materials are promising for the realization of large area and flexible lighting devices. The deposition of 2D perovskites, however, requires wide range solvents that are incompatible with commodity polymers used for structural support and light management. Here we demonstrate coupling of broad-emitting 2,2-(ethylenedioxy)bis(ethylammonium)PbCl4 perovskite with solution processed polymer distributed Bragg reflectors on both rigid fused silica and flexible polymer substrates. The optical functions of the chemically engineered perovskite were determined by ellipsometric measurements and used to design dielectric multilayer structures with photonic bandgap tunable over the entire visible range. The resulting photonic structures control directionality and spectral enhancement or suppression of the perovskite photoluminescence, in agreement with simple analytical optical models. These results pave the way to the development of ...

Cesium-Containing Perovskite Solar Cell Based on Graphene/TiO2 Electron Transport Layer

Graphene shows remarkably high mobility, electronic and thermal conductivity, which have been widely incorporated in solar cells as electron transport highway. Herein, graphene is incorporated in TiO2 compact layer as electron transport layer for cesium-containing perovskite (Cs0.1(CH3NH3)0.9PbI3) solar cell. Introducing graphene effectively improves mobility of electron transport layer and reduce the quenching of perovskite photoluminescence, which is correlated with improved electron transport and extraction property. A significant improvement of power conversion efficiency from 11.2% to 15.4% is achieved (37% enhancement) through simply introducing graphene in TiO2 compact layer. The improved efficiency is mainly due to the improved fill factor. This work highlights the roles of graphene in facilitating electron transport and extraction at interface of perovskite and electron transport layer.

An Investigation into Electric Field-Modulated Photoluminescence of Perovskite solar cells

ABSTRACTElectric field-modulated photoluminescence (PL) of perovskite solar cells is investigated to gain deeper insight about the role of the mobile ions in organometal halide perovskites. The PL intensity of perovskite solar cells show significant dependence on the polarity of the external electric field and the voltage scanning direction. This phenomenon is discussed in the framework of an ion migration mechanism, which has been widely accounted for the current density-voltage (J-V) hysteresis in perovskite solar cells. The result suggests that the mobile ions not only change the internal electric field of perovskite solar cells, but also have an effect on the recombination of photogenerated charge carriers.

Surface Decorating of CH₃NH₃PbBr₃ Nanoparticles with the Chemically Adsorbed Perylenetetracarboxylic Diimide.

An organic dye-modified organolead halide CH3NH3PbBr3 nanoparticle (cubic) is prepared successfully by using a perylenetetracarboxylic diimide (PDI) bearing an -NH3(+) headgroup as the capping ligand. The nanopartilces are homogeneous with high crystallinity. The photoluminescence of perovskite is quenched completely by the chemically adsorbed PDI molecules. This efficient fluorescence quenching has confirmed that the PDI molecules are anchored on the surface of CH3NH3PbBr3 nanoparticle. The resulting nanoparticles can be dispersed in organic solvents, and the resulting dispersion remains stable for days. This result provides a general guideline for surface engineering of organolead halide CH3NH3PbBr3 nanoparticles.

Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold.

A light-induced photoluminescence (PL) enhancement in surface-deposited methylammonium lead iodide (CH3NH3PbI3) perovskites was investigated in detail using time-resolved luminescence microscopy. We found the PL intensity to increase up to three orders of magnitude upon light illumination with an excitation power density of 0.01-1 W cm(-2). The PL enhancement is accompanied by an increase of the PL lifetime from several nanoseconds to several hundred nanoseconds and also by an increase of the initial amplitude of the PL decay. The latter suggests excited state quenching at the subpicosecond timescale. We propose a model where the trapping sites responsible for non-radiative charge recombination can be de-activated by a photochemical reaction involving oxygen. The reaction zone is spatially limited by the excitation light-penetration depth and diffusion length of the charge carriers. The latter increases in the course of the light-curing process making the reaction zone spreading from the surface towards the interior of the crystal. The PL enhancement can be reversed by switching on/off the excitation light or switching the atmosphere between oxygen and nitrogen. Slow diffusion of the reactants and products and equilibrium between the active and "cured" trapping sites are proposed to be the reasons for peculiar responses of PL to such varied experimental conditions.

Efficiency Enhancement of Perovskite Solar Cells through Fast Electron Extraction: The Role of Graphene Quantum Dots

We report on a significant power conversion efficiency improvement of perovskite solar cells from 8.81% to 10.15% due to insertion of an ultrathin graphene quantum dots (GQDs) layer between perovskite and TiO2. A strong quenching of perovskite photoluminescence was observed at ∼760 nm upon the addition of the GQDs, which is pronouncedly correlated with the increase of the IPCE and the APCE of the respective cells. From the transient absorption measurements, the improved cell efficiency can be attributed to the much faster electron extraction with the presence of GQDs (90-106 ps) than without their presence (260-307 ps). This work highlights that GQDs can act as a superfast electron tunnel for optoelectronic devices.