Improved hole-transporting property via HAT-CN for perovskite solar cells without lithium salts

Lowering Molecular Symmetry To Improve the Morphological Properties of the Hole-Transport Layer for Stable Perovskite Solar Cells

Inspired by the structural feature of the classical hole-transport material (HTM), Spiro-OMeTAD, many analogues based on a highly symmetrical spiro-core were reported for perovskite solar cells (PSCs). However, these HTMs were prone to crystallize because of the high molecular symmetry, forming non-uniform films, unfavorable for the device stability and large-area processing. By lowering the symmetry of spiro-core, we report herein a novel spirobisindane-based HTM, Spiro-I, which could form amorphous films with high uniformity and morphological stability. Compared to the Spiro-OMeTAD-based PSCs, those containing Spiro-I exhibit similar efficiencies for small area but higher ones for large area (1 cm² ), and especially much higher air stability (retaining 80 % of initial PCE after 2400 h storage without encapsulation). Moreover, the Spiro-I can be synthesized from a cheap starting material bisphenol A and used with a small amount for the device fabrication.

Bright monolayer tungsten disulfide via exciton and trion chemical modulations

Atomically thin transition metal dichalcogenides (TMDCs) with exceptional electrical and optical properties have drawn tremendous attention for use in novel optoelectronic applications as photodetectors, transistors, light emitters, etc. However, electron bound trions formed through the combination of neutral excitons and electrons significantly decrease the photoluminescence (PL) efficiency of TMDCs. In this study, we report a simple yet efficient chemical doping strategy to modulate the optical properties of monolayer tungsten disulfide (WS2). As a demonstrative example, a chemically doped monolayer of WS2 exhibits remarkable PL enhancement of about one order of magnitude higher than that of pristine WS2. This outstanding PL enhancement is attributed to the fact that excess electrons, which promote the formation of electron-bound trions, are reduced in number through charge transfer from WS2 to the chemical dopant. Furthermore, an improved degree of circular polarization from ∼9.0% to ∼41.5% was also observed in the chemically doped WS2 monolayer. This work describes a feasible strategy to manipulate the optical properties of TMDCs via exciton modulation, making TMDCs promising candidates for versatile semiconductor-based photonic devices.

Defects in metal triiodide perovskite materials towards high-performance solar cells: origin, impact, characterization, and engineering

The progress of defect science in metal triiodide perovskite is critically reviewed, including the origin, impacts, characterization, and engineering.

Water-Soluble Polymeric Interfacial Material for Planar Perovskite Solar Cells

Interfacial materials play a critical role in photoelectric conversion properties as well as the anomalous hysteresis phenomenon of the perovskite solar cells (PSCs). In this article, a water-soluble polythiophene PTEBS was employed as a cathode interfacial material for PSCs. Efficient energy level aligning and improved film morphology were obtained due to an ultrathin coating of PTEBS. Better ohmic contact between the perovskite layer and the cathode also benefits the charge transport and extraction of the device. Moreover, less charge accumulation at the interface weakens the polarization of the perovskite resulting in a relatively quick response of the modified device. The ITO/PTEBS/CH₃NH₃PbI₃/spiro-MeOTAD/Au cells by an all low-temperature process achieved power conversion efficiencies of up to 15.4% without apparent hysteresis effect. Consequently, the utilization of this water-soluble polythiophene is a practical approach for the fabrication of highly efficient, large-area, and low-cost PSCs and compatible with low-temperature solution process, roll-to-roll manufacture, and flexible application.

Stability of Perovskite Solar Cells: A Prospective on the Substitution of the A Cation and X Anion

In recent years, organometal trihalide perovskites have emerged as promising materials for low-cost, flexible, and highly efficient solar cells. Despite their processing advantages, before the technology can be commercialized the poor stability of the organic-inorganic hybrid perovskite materials with regard to humidity, heat, light, and oxygen has be to overcome. Herein, we distill the current state-of-the-art and highlight recent advances in improving the chemical stability of perovskite materials by substitution of the A-cation and X-anion. Our hope is to pave the way for the rational design of perovskite materials to realize perovskite solar cells with unprecedented improvement in stability.

Hexagonal β-NaYF4:Yb(3+), Er(3+) Nanoprism-Incorporated Upconverting Layer in Perovskite Solar Cells for Near-Infrared Sunlight Harvesting

Hexagonal β-NaYF4:Yb(3+), Er(3+) nanoprisms, successfully prepared using a hydrothermal method, were incorporated into CH3NH3PbI3 perovskite solar cells (PSCs) as an upconverting mesoporous layer. Due to their near-infrared (NIR) sunlight harvesting, the PSCs based on the upconverting mesoporous layer exhibited a power conversion efficiency of 16.0%, an increase of 13.7% compared with conventional TiO2 nanoparticle-based PSCs (14.1%). This result suggests that the hexagonal β-NaYF4:Yb(3+), Er(3+) nanoprisms expand the absorption range of the PSC via upconversion photoluminescence, leading to an enhancement of the photocurrent.

Novel Combination of Efficient Perovskite Solar Cells with Low Temperature Processed Compact TiO2 Layer via Anodic Oxidation

In this work, a facile and low temperature processed anodic oxidation approach is proposed for fabricating compact and homogeneous titanium dioxide film (AO-TiO2). In order to realize morphology and thickness control of AO-TiO2, the theory concerning anodic oxidation (AO) is unveiled and the influence of relevant parameters during the process of AO such as electrolyte ingredient and oxidation voltage on AO-TiO2 formation is observed as well. Meanwhile, we demonstrate that the planar perovskite solar cells (p-PSCs) fabricated in ambient air and utilizing optimized AO-TiO2 as electron transport layer (ETL) can deliver repeatable power conversion efficiency (PCE) over 13%, which possess superior open-circuit voltage (Voc) and higher fill factor (FF) compared to its counterpart utilizing conventional high temperature processed compact TiO2 (c-TiO2) as ETL. Through a further comparative study, it is indicated that the improvement of device performance should be attributed to more effective electron collection from perovskite layer to AO-TiO2 and the decrease of device series resistance. Furthermore, hysteresis effect about current density-voltage (J-V) curves in TiO2-based p-PSCs is also unveiled.

Strategic improvement of the long-term stability of perovskite materials and perovskite solar cells

This review provides a comprehensive overview of the recent strategies aimed at enhancing the long-term stability of perovskite materials and perovskite solar cells (PSCs). It also extensively discusses the stability problem of perovskite materials and PSCs from perspectives of experimental tests and theoretical calculations.

Undesirable role of remnant PbI2 layer on low temperature processed planar perovskite solar cells

In this work, we carefully study the influence of the remnant PbI₂ on the performance of planar PSCs including efficiency and thermal stability by varying the PbI₂ stoichiometry of the resultant CH₃NH₃PbI₃.

Novel Carbazole-Based Hole-Transporting Materials with Star-Shaped Chemical Structures for Perovskite-Sensitized Solar Cells

Novel carbazole-based hole-transporting materials (HTMs), including extended π-conjugated central core units such as 1,4-phenyl, 4,4'-biphenyl, or 1,3,5-trisphenylbenzene for promoting effective π-π stacking as well as the hexyloxy flexible group for enhancing solubility in organic solvent, have been synthesized as HTM of perovskite-sensitized solar cells. A HTM with 1,3,5-trisphenylbenzene core, coded as SGT-411, exhibited the highest charge conductivity caused by its intrinsic property to form crystallized structure. The perovskite-sensitized solar cells with SGT-411 exhibited the highest PCE of 13.00%, which is 94% of that of the device derived from spiro-OMeTAD (13.76%). Time-resolved photoluminescence spectra indicate that SGT-411 shows the shortest decay time constant, which is in agreement with the trends of conductivity data, indicating it having fastest charge regeneration. In this regard, a carbazole-based HTM with star-shaped chemical structure is considered to be a promising candidate HTM.

Open-shell doublet character in a hexaazatrinaphthylene trianion complex

Three-electron reduction of hexaazatrinaphthylene (HAN) with a magnesium(I) reagent leads to [(HAN){Mg(nacnac)}3] (1), containing a [HAN](3-) ligand with a spin of S = 1/2. Ab initio calculations reveal that the [HAN](3-) ligand in 1 has a ground-state wave function with multiconfigurational properties, and can be described as a triradicaloid species with a small amount of open-shell doublet character.