Stabilizing perovskite solar cells with modified indium oxide electron transport layer

Despite the impressive progress, the perovskite solar cells are still under the stage of laboratory research, mainly because of their inferior operational stability. To improve the device lifetime, one of the most important strategies is to eliminate the undesirable side reactions between the functional layers. In this study, we present the thermal oxidation method to yield high-quality pristine and modified indium oxide films applied as efficient electron transport layers (ETLs) for perovskite cells in a planar n-i-p configuration. The cells incorporating In2O3 as ETL material can deliver comparable efficiencies with the reference SnO2- based devices while showing much superior operational stability. We attributed the observed stabilizing effect of indium oxide to its reduced chemical activity at the interface with the perovskite absorber layer. In particular, In2O3 can hardly oxidize I- to molecular iodine on the contrary to SnO2 and TiO2 known for their photocatalytic activity. We believe that this study may provide researchers with general guidelines to develop a large variety of ETL materials for efficient yet stable perovskite cells

Reactive modification of zinc oxide with methylammonium iodide boosts the operational stability of perovskite solar cells

Low operational stability of perovskite solar cells represents a major obstacle for practical implementation of this technology. In that context, ZnO was considered as a promising electron transport material with suppressed oxidizing properties as compared to SnO2 and TiO2. However, the first studies revealed the chemical instability of the interface between lead halide perovskites and zinc oxide, whereas the underlying reasons are still under active debates. Still, the interfacial instability issues made ZnO a largely overlooked electron transport layer despite its excellent optoelectronic properties. This study presents a novel approach to the zinc oxide surface modification with methylammonium iodide that suppresses further reactions with the adjacent perovskite absorber layer. Consequently, the solar cells based on CH3NH3PbI3 exhibited largely improved thermal stability. Furthermore, the application of Cs0.12[HC(NH2)2]0.88PbI3 as absorber material in devices with the modified ZnO electron transport layer resulted in 82% retention of the initial efficiency after aging for 2100 h at 50 mW cm-2 and 65 ?C. On the contrary, the reference cells fabricated with the pristine non-modified ZnO degraded completely under the same conditions. We attribute the revealed stabilization effect of the methylammonium iodide treatment to passivation of the reactive ZnO surface and inhibiting the parasitic interfacial chemistry leading to the lead iodide formation. To our best knowledge, here we have demonstrated the highest operational stability for the perovskite cells when using ZnO-based ETL

Joint Studies of Spin Frustration Induced by Doping Small ZnSe Nanoparticles with Fe Atoms

Abstract As a 1.8 nm ZnSe nanocrystal is progressively doped with 1%, 5%, and 10% Fe, it shows a progressive change in its magnetic properties from a superparamagnetic FM‐dominated exchange type to an onset of AFM exchange with evidence of spin frustration. Magnetization measurements allow to obtain exchange coupling constants that are compared to the results of a Broken‐Symmetry Density Functional Theory (BS‐DFT) model of a doped (ZnSe)34 cluster. DFT shows a capability to reproduce the experimental pattern of the increasing influence of AFM exchange as doping concentration increases. The material phase segregates at the edges where strained rhombic surface sites are the preferred doping sites of iron. Large concentrations of iron leads to the formation of Fe clusters and complex exchange patterns that result in spin frustration in some iron trimers but none in the others. The spin frustration of these complex systems by assuming mirror symmetry of the sites when fitting by using BS‐DFT formalism is classified and analyzed. While some individual J constants obtained have significant errors, the averaged exchange constants are generally in good agreement with our experimental data

Surface Passivation for Efficient Bifacial HTL-free Perovskite Solar Cells with SWCNT Top Electrodes

Publisher Copyright: © 2021 American Chemical Society.Building-integrated photovoltaics is an emerging field that demands approaches to deliver efficient and flexible photovoltaic cells at a low cost. In this work, high-quality single-walled carbon nanotube (SWCNT) films were utilized as an electrode for the hole-transport-layer (HTL)-free perovskite solar cells using a methodology compatible with scalable low-temperature roll-to-roll fabrication. We report a simple passivation strategy of the perovskite/SWCNT interface using methylammonium iodide, which dramatically enhances the performance of the cells, delivering power conversion efficiencies of up to 16.7%. We believe that the device configuration presented here will facilitate the development of a generation of bifacial perovskite solar cells for integrated photovoltaics and tandems.Peer reviewe

Theoretical Modeling of the Magnetic Behavior of Thiacalix[4]arene Tetranuclear Mn^II₂Gd^III₂ and Co^II₂Eu^III₂ Complexes

In view of a wide perspective of 3d–4f complexes in single-molecule magnetism, here we propose an explanation of the magnetic behavior of the two thiacalix[4]­arene tetranuclear heterometallic complexes Mn^II₂Gd^III₂ and Co^II₂Eu^III₂. The energy pattern of the Mn^II₂Gd^III₂ complex evaluated in the framework of the isotropic exchange model exhibits a rotational band of the low-lying spin excitations within which the Landé intervals are affected by the biquadratic spin–spin interactions. The nonmonotonic temperature dependence of the χ<i>T</i> product observed for the Mn^II₂Gd^III₂ complex is attributed to the competitive influence of the ferromagnetic Mn–Gd and antiferromagnetic Mn–Mn exchange interactions, the latter being stronger (<i>J</i>(Mn, Mn) = −1.6 cm^–1, <i>J</i>_s(Mn, Gd) = 0.8 cm^–1, <i>g</i> = 1.97). The model for the Co^II₂Eu^III₂ complex includes uniaxial anisotropy of the seven-coordinate Co^II ions and an isotropic exchange interaction in the Co^II₂ pair, while the Eu^III ions are diamagnetic in their ground states. Best-fit analysis of χ<i>T</i> versus <i>T</i> showed that the anisotropic contribution (arising from a large zero-field splitting in Co^II ions) dominates (weak-exchange limit) in the Co^II₂Eu^III₂ complex (<i>D</i> = 20.5 cm^–1, <i>J</i> = −0.4 cm^–1, <i>g</i>_Co = 2.22). This complex is concluded to exhibit an easy plane of magnetization (arising from the Co^II pair). It is shown that the low-lying part of the spectrum can be described by a highly anisotropic effective spin-¹/₂ Hamiltonian that is deduced for the Co^II₂ pair in the weak-exchange limit

The first photochromic bimetallic assemblies based on Mn(III) and Mn(II) Schiff-base (salpn, dapsc) complexes and pentacyanonitrosylferrate

International audienceFour cyano-bridged bimetallic complexes, \[Mn(salpn)](2)[Fe(CN)(5)NO]\(n) (1), \[Mn(salpn)(CH3OH)](4)[Mn(CN)(5)NO]\[C(CN)(3)]center dot 3H(2)O (2), \[Mn(dapsc)][Fe(CN)(5)NO]center dot 0.5CH(3)OH center dot 0.25H(2)O\(n) (3) and \[Mn(salpn)(CH3OH)](4)[Fe(CN)(5)NO]\(ClO4)(2)center dot 4H(2)O (4), where salpn(2-) = N, N'-1,3-propylene-bis(salicylideneiminato) dianion and dapsc = 2,6-diacetylpyridine-bis(semicarbazone), have been synthesized and structurally characterized by single crystal X-ray diffraction. In 1, the nitroprusside anion [Fe(CN)(5)NO](2-) coordinates with four [Mn(salpn)](+) via four co-planar CN- groups, whereas each [Mn(salpn)](+) links two [Fe(CN)(5)NO](2-) ions, which results in a two-dimensional network. The structure of 3 contains two independent neutral infinite chains \[Mn(dapsc)][Fe(CN)(5)(NO)]\(infinity) consisting of alternating cationic [Mn-II(dapsc)](2+) and anionic [Fe-II(CN)(5)(NO)](2-) units connected through cyanide bridges. The cation complexes 2 and 4 have a pentanuclear molecular structure in which four [Mn(salpn)(MeOH)](+) fragments are linked by the [Mn(CN)(5)NO](3-) or [Fe(CN)(5)(NO)](2-) moieties, respectively. The magnetic and photochromic properties of 1 and 3 have been studied. The thermal magnetic behaviour of the complexes indicates the presence of weak antiferromagnetic interactions between Mn3+ or Mn2+ mediated by diamagnetic [Fe(CN)(NO)-N-5](2-) bridges. Irradiation of 1 and 3 with light gives birth to the long-lived metastable states of nitroprusside

Improving stability of perovskite solar cells using fullerene-polymer composite electron transport layer

Perovskite solar cells (PSCs) have attracted significant attention due to their high efficiency and potential for low-cost manufacturing, but their commercialization is strongly impeded by low operational stability. The engineering of charge-transport layer materials have been recognized as an effective strategy to improve both stability and performance of PSCs. Here, we introduce a pyrrolo[3,4-c]pyrrole-1,4-dione-based n-type copolymer as an electron transport material for perovskite solar cells. Using a composite of this polymer with the fullerene derivative [60]PCBM delivered an efficiency of 16.4% and enabled long-term operational stability of p-i-n perovskite solar cells

Rational Design of Fullerene Derivatives for Improved Stability of p-i-n Perovskite Solar Cells

Perovskite solar cells (PSCs) with p-i-n architecture attracted particular attention from the research community due to their simple and scalable fabrication at low temperatures. However, the operational stability of p-i-n PSCs has to be improved, which requires the development of advanced charge transport interlayers. Fullerene derivatives such as phenyl-C61-butyric acid methyl ester (PC61BM) are commonly used as electron transport layer (ETL) materials in PSCs, though they strongly compromise the device stability. Indeed, it has been shown that PC61BM films actively absorb volatile products resulting from photodegradation of lead halide perovskites and transport them towards top metal electrode. Thus, there is an urgent need for development of new fullerene-based electron transport materials with improved properties, in particular the ability to heal defects on the perovskite films surface and block the diffusion of volatile perovskite photodegradation products. To address this challenge, a systematic variation of organic addends structure should be performed in order to tailor the properties of fullerene derivatives. Herein, we rationally designed a series of fullerene derivatives with different side chains and explored their performance as ETL materials in perovskite solar cells. It has been shown that among all studied compounds, a methanofullerene with thiophene pendant group enables both high efficiency and improved device operational stability. The obtained results suggest that further engineering of fullerene-based materials could pave a way for the development of advanced ETL materials enabling long lifetimes of p-i-n perovskite solar cells

Enhanced Pseudocapacitive Performance of α‑MnO₂ by Cation Preinsertion

Although the theoretical capacitance of MnO₂ is 1370 F g^–1 based on the Mn³⁺/Mn⁴⁺ redox couple, most of the reported capacitances in literature are far below the theoretical value even when the material goes to nanoscale. To understand this discrepancy, in this work, the electrochemical behavior and charge storage mechanism of K⁺-inserted α-MnO₂ (or K_<i>x</i>MnO₂) nanorod arrays in broad potential windows are investigated. It is found that electrochemical behavior of K_<i>x</i>MnO₂ is highly dependent on the potential window. During cyclic voltammetry cycling in a broad potential window, K⁺ ions can be replaced by Na⁺ ions, which determines the pseudocapacitance of the electrode. The K⁺ or Na⁺ ions cannot be fully extracted when the upper cutoff potential is less than 1 V vs Ag/AgCl, which retards the release of full capacitance. As the cyclic voltammetry potential window is extended to 0–1.2 V, enhanced specific capacitance can be obtained with the emerging of new redox peaks. In contrast, the K⁺-free α-MnO₂ nanorod arrays show no redox peaks in the same potential window together with much lower specific capacitance. This work provides new insights on understanding the charge storage mechanism of MnO₂ and new strategy to further improve the specific capacitance of MnO₂-based electrodes