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Recently, perovskite solar cells have shown excellent performance under indoor light conditions. In a new approach using directional illumination combined with nanoscale scanning probe microscopy (SPM) characterization, morphology dependent‐charge transport measurements are performed to provide a comprehensive understanding of the optoelectronic behavior of (FAPbI3)0.85(MAPbBr3)0.15 containing 5 vol% cesium (Cs5vol%) with various electron transport layers (ETLs), i.e., SnO2, c‐TiO2, and [6,6]‐phenyl‐C61‐butyric acid methyl ester/SnO2 under indoor light. This approach allows the identification of the charge transport properties of the perovskite film and the perovskite/ETL interface separately. The light is applied from the top of the perovskite film to study the electronic properties of the surface. Lower photocurrent and lower surface photovoltage (SPV) are observed under top‐illumination conditions. The electronic interface behavior is investigated using bottom‐illumination and short excitation wavelengths, such as blue LED light. Higher photocurrent and higher SPV are observed under blue light illumination from the bottom. These results suggest that the charge transport capability is enhanced near the p–n junction. Conductive atomic force microscopy results show that SnO2 enhances the charge collection properties of the perovskite's grain boundaries (GBs). Kelvin probe force microscopy results confirm that SnO2 exhibits homogeneous and high surface potential because of the lowest trap states at GBs. [ABSTRACT FROM AUTHOR]

A series of chiral stereoisomers of electron transporting materials with two chiral substituents is rationally designed and synthesized, and the influence of stereoisomerism on their physical and electronic properties is investigated to demonstrate highly efficient and stable perovskite solar cells (PSCs). Compared to mesomeric naphthalene diimide (NDI) derivatives, which have heterochiral side groups with centrosymmetric molecular packing of symmetric‐shaped conformers in the crystalline state, enantiomeric NDI derivatives have homochiral side groups that exhibit non‐centrosymmetric molecular packing of asymmetric‐shaped conformers in the crystalline state and exhibit better solution processability based on one order of magnitude higher solubility. A similar trend is observed in different rylene diimide stereoisomers based on larger semiconducting core perylene diimide. The PSCs based on NDI enantiomers with good film‐forming ability and a very high lowest phase transition temperature (Tlowest) of 321 °C exhibit a high and uniform average power conversion efficiency (PCE) of 19.067 ± 0.654%. These PSCs also have a high temporal device stability, with less than 10% degradation of the PCE at 100 °C for 1000 h without encapsulation. Therefore, chiral stereoisomer engineering of charge transporting materials is a potential approach to achieve high solution processability, excellent performance, and significant temporal stability in organic electronic devices. [ABSTRACT FROM AUTHOR]

A design strategy is proposed for electron‐transporting materials (ETMs) with homochiral asymmetric‐shaped groups for highly efficient non‐fullerene perovskite solar cells (PSCs). The electron transporting N,N′‐bis[(R)‐1‐phenylethyl]naphthalene‐1,4,5,8‐tetracarboxylic diimide (NDI‐PhE) consists of two asymmetric‐shaped chiral (R)‐1‐phenylethyl (PhE) groups that act as solubilizing groups by reducing molecular symmetry and increasing the free volume. NDI‐PhE exhibits excellent film‐forming ability with high solubility in various organic solvents [about two times higher solubility than the widely used fullerene‐based phenyl‐C61‐butyric acid methyl ester (PCBM) in o‐dichlorobenzene]. NDI‐PhE ETM‐based inverted PSCs exhibit very high power conversion efficiencies (PCE) of up to 20.5 % with an average PCE of 18.74±0.95 %, which are higher than those of PCBM ETM‐based PSCs. The high PCE of NDI‐PhE ETM‐based PSCs may be attributed to good film‐forming abilities and to three‐dimensional isotropic electron transporting capabilities. Therefore, introducing homochiral asymmetric‐shaped groups onto charge‐transporting materials is a good strategy for achieving high device performance. Turn up the power: Homochiral asymmetric‐shaped electron‐transporting materials (ETMs) exhibit excellent film‐forming ability with high solubility in various organic solvents. The homochiral ETM‐based inverted perovskite solar cells exhibit very high power conversion efficiencies (PCE) up to 20.5 % and very high reproducibility with an average PCE of 18.74±0.95 %. [ABSTRACT FROM AUTHOR]

Organic electron‐transporting materials (ETMs) with low‐temperature solution processability and high electron‐transfer/transport characteristics have received significant attention for their use in high‐performance perovskite solar cells (PSCs). In contrast to widely investigated fullerene‐based organic ETMs for PSCs, only a few types of non‐fullerene‐based ETMs have been developed. In this Concept article, a representative design concept for non‐fullerene ETMs is described for use in normal (n‐i‐p) and inverted (p‐i‐n) type PSCs. On the basis of a discussion on ETM requirements for PSCs, recently developed non‐fullerene polymeric and small‐molecule‐based ETMs for PSCs are highlighted, alongside various other approaches for enhancing PSC device performance, such as using additional dopants and introducing amine terminal groups in the ETMs and ETM‐based interlayers. This Concept provides a basic design concept for non‐fullerene‐based ETMs in PSCs. A place in the sun: This Concept article describes the representative design concept of non‐fullerene organic electron‐transporting materials (ETMs) for normal‐ and inverted‐structured perovskite solar cells (PSCs). A discussion of the requirements of ETMs for PSCs is also discussed (HTM=hole‐transporting material; TCO=transparent conducting oxide). [ABSTRACT FROM AUTHOR]

Abstract: This study reports a new nonfullerene electron transporting material (ETM) based on naphthalene diimide (NDI) small molecules for use in high‐performance perovskite solar cells (PSCs). These solar cells simultaneously achieve high power conversion efficiency (PCE) of over 20% and long‐term stability. New NDI‐ID (N,N′‐Bis(1‐indanyl)naphthalene‐1,4,5,8‐tetracarboxylic diimide) consisting of an N‐substituted indane group having simultaneous alicyclic and aromatic characteristics is synthesized by a low‐cost, one‐step reaction, and facile purification method. The partially flexible characteristics of an alicyclic cyclopentene group on indane groups open the possibility of low‐temperature solution processing. The conformational rigidity and aromaticity of phenyl and alicyclic groups contribute to high temporal stability by strong secondary bonds. NDI‐ID has herringbone packed semiconducting NDI cores that exhibit up to 0.2 cm2 V−1 s−1 electron mobility in field effect transistors. The inverted PSCs based on CH(NH2)2PbI3–xBrx with NDI‐ID ETM exhibit very high PCEs of up to 20.2%, which is better than that of widely used PCBM (phenyl‐C61‐butyric acid methyl ester) ETM‐based PSCs. Moreover, NDI‐ID‐based PSCs exhibit very high long‐term temporal stability, retaining 90% of the initial PCE after 500 h at 100 °C with 1 sun illumination without encapsulation. Therefore, NDI‐ID is a promising ETM for highly efficient, stable PSCs. [ABSTRACT FROM AUTHOR]

Chiral Stereoisomer Engineering: Chiral Stereoisomer Engineering of Electron Transporting Materials for Efficient and Stable Perovskite Solar Cells (Adv. Funct. Keywords: chirality; electron transporting materials; perovskite solar cells; stereoisomers EN chirality electron transporting materials perovskite solar cells stereoisomers 1 1 1 03/28/20 20200324 NES 200324 In article number 1905951, Jong H. Kim, Sang Hyuk Im, O-Pil Kwon, and co-workers report a series of electron transporting homochiral and heterochiral stereoisomers of naphthalene diimide crystalline materials and show simultaneous achievement of low-temperature solution processability, high device performance, and long-term temporal device stability. Chirality, electron transporting materials, perovskite solar cells, stereoisomers. [Extracted from the article]

The Cover Feature shows the homochiral asymmetric‐shaped electron transporting materials (ETMs) exhibiting excellent film‐forming ability with high solubility in various organic solvents. The homochiral ETM‐based inverted perovskite solar cells exhibit very high power conversion efficiency with high reproducibility. Introducing homochiral asymmetric‐shaped groups on ETMs is good design strategy for various electronic devices. More information can be found in the Full Paper by S.‐K. Jung, J. H. Heo et al. on page 224 in Issue 1, 2019 (DOI: 10.1002/cssc.201802234). [ABSTRACT FROM AUTHOR]

The Front Cover shows high performance perovskite solar cells (PSCs) based on non‐fullerene organic electron transporting materials (ETMs). Organic ETMs are very attractive for high performance PSCs due to their efficient electron transporting characteristics and low‐temperature solution processability. In their Concept, S.‐K. Jung, D. S. Lee et al. discuss representative design concepts of non‐fullerene polymeric and small molecular‐based ETMs for normal and inverted PSCs and their ETM requirements. More information can be found in the Concept by S.‐K. Jung, D. S. Lee et al. on page 3882 in Issue 22, 2018 (DOI: 10.1002/cssc.201801908). [ABSTRACT FROM AUTHOR]

[Display omitted] • We investigated interface dipole effects on indoor perovskite solar cells. • QDPPO enabled homogeneous charge distribution and suppressed recombination. • Perovskite solar cells based on QDPPO exhibited iPCE of 36.90% at 800 lux light. • Mini-modules based on QDPPO generated power output of 2.4 mW at 1,000 lux light. Indoor-light harvesting-technology based on perovskite solar cells have attracted significant attention owing to their promising photovoltaic properties as indoor power generators. We investigated the effect of interfacial dipoles on the performance of perovskite solar cells in low-intensity indoor light environments. Interfacial dipoles were controlled by inserting different polar layers with different molecular dipole moments (BCP, QPPO and QDPPO) on top of electron transport layers (ETLs). Significantly improved uniformity of interfacial dipoles, in the QDPPO layer, effectively reduced charge recombination and enabled persistent fill factors (FF's) under low-intensity light environments. Perovskite solar cells based on QDPPO exhibited indoor power density (iPD) and indoor power conversion efficiency (iPCE) of 65.63 μ W/cm2 and 27.49 % under 800 lux LED, which were further enhanced up to 88.09 μ W/cm2 and 36.90 % by employing additional passivation layer under 800 lux LED. Finally, using QDPPO, we successfully demonstrated perovskite photovoltaic mini-modules with a high power output of 2.4 mW under a 1,000 lux halogen, which can be applied in Internet-of-Things sensors under indoor light conditions. [ABSTRACT FROM AUTHOR]

Herein, we report the dual functionality of a single n-type gallium nitride (n-GaN) layer as an electron transporter and transparent conductor, which has applications in reusable organic solar cells. After silicon doping with an optimized electron concentration, thin-film layer of GaN showed exceptional electrical properties including charge carrier mobility of 161 cm2 V−1s−1, electrical conductivity of 1.4ⅹ106 S cm−1, and sheet resistance of 11.1 Ω cm−2. Organic solar cells based on n-GaN exhibited power conversion efficiency comparable to those based on a conventional ITO/ZnO bilayered cathode. Furthermore, the n-GaN substrates exhibited reusability; due to excellent chemical stability of n-GaN, the reconstructed organic solar cells maintained their initial performance after the substrates were recycled. We suggest a new type of reusable n-GaN cathode layer featuring an integrated electron transporting layer and transparent electrode. Image 1 • Dual functionality of GaN as an electron transporter and transparent conductor for solar cell have been investigated. • Optimized N-doped GaN showed high charge carrier mobility of 161 cm2/Vs and low sheet resistance of 11.1 Ω/cm2. • N-type GaN substrates featured exceptional chemical stability which allowed recyclable uses for polymer solar cells. [ABSTRACT FROM AUTHOR]