Exploring the Effects of the Pb²⁺ Substitution in MAPbI₃ on the Photovoltaic Performance of the Hybrid Perovskite Solar Cells

Here we report a systematic study of the Pb²⁺ substitution in the hybrid iodoplumbate MAPbI₃ with a series of elements affecting optoelectronic, structural, and morphological properties of the system. It has been shown that even partial replacement of lead with Cd²⁺, Zn²⁺, Fe²⁺, Ni²⁺, Co²⁺, In³⁺, Bi³⁺, Sn⁴⁺, and Ti⁴⁺ results in a significant deterioration of the photovoltaic characteristics. On the contrary, Hg-containing hybrid MAPb_1–<i>x</i>Hg_<i>x</i>I₃ salts demonstrated a considerably improved solar cell performance at optimal mercury loading. This result opens up additional dimension in the compositional engineering of the complex lead halides for designing novel photoactive materials with advanced optoelectronic and photovoltaic properties

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

Exploring the Photovoltaic Performance of All-Inorganic Ag₂PbI₄/PbI₂ Blends

We present an all-inorganic photoactive material composed of Ag₂PbI₄ and PbI₂, which shows unexpectedly good photovoltaic performance in planar junction solar cells delivering external quantum efficiencies of ∼60% and light power conversion efficiencies of ∼3.9%. The revealed characteristics are among the best reported to date for metal halides with nonperovskite crystal structure. Most importantly, the obtained results suggest a possibility of reaching high photovoltaic efficiencies for binary and, probably, also ternary blends of different inorganic semiconductor materials. This approach, resembling the bulk heterojunction concept guiding the development of organic photovoltaics for two decades, opens wide opportunities for rational design of novel inorganic and hybrid materials for efficient and sustainable photovoltaic technologies

Influence of Oxygen Ion Migration from Substrates on Photochemical Degradation of CH3NH3PbI3 Hybrid Perovskite

Measurements of XPS survey, core levels (N 1s, O 1s, Pb 4f, I 3d), and valence band (VB) spectra of CH3NH3PbI3 (MAPbI3) hybrid perovskite prepared on different substrates (glass, indium tin oxide (ITO), and TiO2) aged under different light-soaking conditions at room temperature are presented. The results reveal that the photochemical stability of MAPbI3 depends on the type of substrate and gradually decreases when glass is replaced by ITO and TiO2. Also, the degradation upon exposure to visible light is accompanied by the formation of MAI, PbI2, and Pb0 products as shown by XPS core levels spectra. According to XPS O 1s and VB spectra measurements, this degradation process is superimposed on the partial oxidation of lead atoms in ITO/MAPbI3 and TiO2/MAPbI3, for which Pb–O bonds are formed due to the diffusion of the oxygen ions from the substrates. This unexpected interaction leads to additional photochemical degradation

Direct Nanoscale Visualization of the Electric-Field-Induced Aging Dynamics of MAPbI₃ Thin Films

Perovskite solar cells represent the most attractive emerging photovoltaic technology, but their practical implementation is limited by solar cell devices’ low levels of operational stability. The electric field represents one of the key stress factors leading to the fast degradation of perovskite solar cells. To mitigate this issue, one must gain a deep mechanistic understanding of the perovskite aging pathways associated with the action of the electric field. Since degradation processes are spatially heterogeneous, the behaviors of perovskite films under an applied electric field should be visualized with nanoscale resolution. Herein, we report a direct nanoscale visualization of methylammonium (MA+) cation dynamics in methylammonium lead iodide (MAPbI3) films during field-induced degradation, using infrared scattering-type scanning near-field microscopy (IR s-SNOM). The obtained data reveal that the major aging pathways are related to the anodic oxidation of I− and the cathodic reduction of MA+, which finally result in the depletion of organic species in the channel of the device and the formation of Pb. This conclusion was supported by a set of complementary techniques such as time-of-flight secondary ion mass spectrometry (ToF-SIMS), photoluminescence (PL) microscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) microanalysis. The obtained results demonstrate that IR s-SNOM represents a powerful technique for studying the spatially resolved field-induced degradation dynamics of hybrid perovskite absorbers and the identification of more promising materials resistant to the electric field

Highly Efficient All-Inorganic Planar Heterojunction Perovskite Solar Cells Produced by Thermal Coevaporation of CsI and PbI₂

We report here all inorganic CsPbI₃ planar junction perovskite solar cells fabricated by thermal coevaporation of CsI and PbI₂ precursors. The best devices delivered power conversion efficiency (PCE) of 9.3 to 10.5%, thus coming close to the reference MAPbI₃-based devices (PCE ≈ 12%). These results emphasize that all inorganic lead halide perovskites can successfully compete in terms of photovoltaic performance with the most widely used hybrid materials such as MAPbI₃

Incorporation of Vanadium(V) Oxide in Hybrid Hole Transport Layer Enables Long-term Operational Stability of Perovskite Solar Cells

Recent studies have shown that charge transport interlayers with low gas permeability can increase the operational lifetime of perovskite solar cells serving as a barrier for migration of volatile decomposition products from the photoactive layer. Herein we present a hybrid hole transport layer (HTL) comprised of p-type polytriarylamine (PTAA) polymer and vanadium(V) oxide (VOx). Devices with PTAA/VOx top HTL reach up to 20% efficiency and demonstrate negligible degradation after 4500 h of light soaking, whereas reference cells using PTAA/MoOx as HTL lose ∼50% of their initial efficiency under the same aging conditions. It was shown that the main origin of the enhanced device stability lies in the higher tolerance of VOx toward MAPbI3 compared to the MoOx interlayer, which tends to facilitate perovskite decomposition. Our results demonstrate that the application of PTAA/VOx hybrid HTL enables long-term operational stability of perovskite solar cells, thus bringing them closer to commercial applications.Peer reviewe

Reversible and Irreversible Electric Field Induced Morphological and Interfacial Transformations of Hybrid Lead Iodide Perovskites

We report reversible and irreversible strain effects and interfacial atomic mixing in MAPbI₃/ITO under influence of external electric bias and photoillumination. Using conductive-probe atomic force microscopy, we locally applied a bias voltage between the MAPbI₃/ITO and the conductive tip and observed local dynamic strain effects and current under conditions of forward bias. We found that the reversible part of the strain is associated with a current spike at the current onset stage and can therefore be related to an electrochemical process accompanied by local molar volume change. Similar partly reversible surface deformation was observed when the tip–sample contact was illuminated by light. Time-of-flight secondary ion mass spectrometry of electrically biased regions revealed massive atomic mixing at the buried MAPbI₃/ITO interface, while the top MAPbI₃ surface, subjected to strong morphological damage at the tip–surface contact, revealed less significant chemical decomposition

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