Double-Mesoscopic Hole-Transport-Material-Free Perovskite Solar Cells: Overcoming Charge-Transport Limitation by Sputtered Ultrathin Al2O3 Isolating Layer

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.

Metal Halide Perovskite/Electrode Contacts in Charge-Transporting-Layer-Free Devices

Metal halide perovskites have drawn substantial interest in optoelectronic devices in the past decade. Perovskite/electrode contacts are crucial for constructing high-performance charge-transporting-layer-free perovskite devices, such as solar cells, field-effect transistors, artificial synapses, memories, etc. Many studies have evidenced that the perovskite layer can directly contact the electrodes, showing abundant physicochemical, electronic, and photoelectric properties in charge-transporting-layer-free perovskite devices. Meanwhile, for perovskite/metal contacts, some critical interfacial physical and chemical processes are reported, including band bending, interface dipoles, metal halogenation, and perovskite decomposition induced by metal electrodes. Thus, a systematic summary of the role of metal halide perovskite/electrode contacts on device performance is essential. This review summarizes and discusses charge carrier dynamics, electronic band engineering, electrode corrosion, electrochemical metallization and dissolution, perovskite decomposition, and interface engineering in perovskite/electrode contacts-based electronic devices for a comprehensive understanding of the contacts. The physicochemical, electronic, and morphological properties of various perovskite/electrode contacts, as well as relevant engineering techniques, are presented. Finally, the current challenges are analyzed, and appropriate recommendations are put forward. It can be expected that further research will lead to significant breakthroughs in their application and promote reforms and innovations in future solid-state physics and materials science.

Structural and compositional properties of 2D CH3NH3PbI3 hybrid halide perovskite: a DFT study

Two-dimensional (2D) hybrid halide perovskites have been scrutinized as candidate materials for solar cells because of their tunable structural and compositional properties. Results based on density functional theory demonstrate its thickness-dependent stability. We have observed that the bandgap decreases from the mono- to quad-layer because of the transformation from 2D towards 3D. Due to the transformation, the carrier mobility is lowered with the corresponding smaller effective mass. On the other hand, the multilayer structures have good optical properties with an absorption coefficient of about 10⁵ cm⁻¹. The calculated absorption spectra lie between 248 nm and 496 nm, leading to optical activity of the 2D multilayer CH₃NH₃PbI₃ systems in the visible and ultraviolet regions. The strength of the optical absorption increases with an increase in thickness. Overall results from this theoretical study suggest that this 2D multilayer CH₃NH₃PbI₃ is a good candidate for photovoltaic and optoelectronic device applications.

We have studied 2D CH₃NH₃PbI₃ and its multilayer halide perovskites. These systems have a high formation energy. The optical properties absorption spectra lie between 248 nm to 496 nm with an absorption coefficient of about 10⁵ cm⁻¹.

Charge transport materials for mesoscopic perovskite solar cells

An overview on recent advances in the fundamental understanding of how interfaces of mesoscopic perovskite solar cells (mp-PSCs) with different architectures, upon incorporating various charge transport layers, influence their performance.

Triple-Mesoscopic Carbon Perovskite Solar Cells: Materials, Processing and Applications

Perovskite solar cells (PSCs) have already achieved comparable performance to industrially established silicon technologies. However, high performance and stability must be also be achieved at large area and low cost to be truly commercially viable. The fully printable triple-mesoscopic carbon perovskite solar cell (mCPSC) has demonstrated unprecedented stability and can be produced at low capital cost with inexpensive materials. These devices are inherently scalable, and large-area modules have already been fabricated using low-cost screen printing. As a uniquely stable, scalable and low-cost architecture, mCPSC research has advanced significantly in recent years. This review provides a detailed overview of advancements in the materials and processing of each individual stack layer as well as in-depth coverage of work on perovskite formulations, with the view of highlighting potential areas for future research. Long term stability studies will also be discussed, to emphasise the impressive achievements of mCPSCs for both indoor and outdoor applications.

Function of Porous Carbon Electrode during the Fabrication of Multiporous-Layered-Electrode Perovskite Solar Cells

We demonstrate the effect of sheet conductivity and infiltration using the example of two graphite types, showing that, in general, the graphite type is very important. Amorphous and pyrolytic graphite were applied to carbon electrodes in fully printable carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs): <glass/F-doped SnO2/compact-TiO2/porous-TiO2+perovskite/porous-ZrO2+perovskite/porous-carbon+perovskite>. The power conversion efficiency (PCE) using amorphous graphite-based carbon (AGC) electrode was only 5.97% due to the low short-circuit photocurrent density (Jsc) value, which was due to the low incident photon-to-current efficiency (IPCE) in the short wavelength region caused by the poor perovskite filling into the porous TiO2-ZrO2 layers. Conversely, using pyrolytic graphite-based carbon (PGC) electrode, Jsc, open-circuit photovoltage (Voc), fill factors (FF), and PCE values of 21.09 mA cm−2, 0.952 V, 0.670, and 13.45%, respectively, were achieved in the champion device. PGC had poorer wettability and a small specific surface area as compared with AGC, but it had better permeability of the perovskite precursor solution into the porous TiO2/ZrO2 layers, and therefore a denser filling and crystallization of the perovskite within the porous TiO2/ZrO2 layers than AGC. It is confirmed that the permeability of the precursor solution depends on the morphology and structure of the graphite employed in the carbon electrode.

Electrochemical Impedance Spectroscopy Analysis of Hole Transporting Material Free Mesoporous and Planar Perovskite Solar Cells

The future photovoltaic technologies based on perovskite materials are aimed to build low tech, truly economical, easily fabricated, broadly deployable, and trustworthy solar cells. Hole transport material (HTM) free perovskite solar cells (PSCs) are among the most likely architectures which hold a distinctive design and provide a simple way to produce large-area and cost-effective manufacture of PSCs. Notably, in the monolithic scheme of the HTM-free PSCs, all layers can be printed using highly reproducible and morphology-controlled methods, and this design has successfully been demonstrated for industrial-scale fabrication. In this review article, we comprehensively describe the recent advancements in the different types of mesoporous (nanostructured) and planar HTM-free PSCs. In addition, the effect of various nanostructures and mesoporous layers on their performance is discussed using the electrochemical impedance spectroscopy (EIS) technique. We bring together the different perspectives that researchers have developed to interpret and analyze the EIS data of the HTM-free PSCs. Their analysis using the EIS tool, the limitations of these studies, and the future work directions to overcome these limitations to enhance the performance of HTM-free PSCs are comprehensively considered.