A single-electron tetrel bond was predicted and characterized in FXH3···CH3 (X = C, Si, Ge, and Sn) complexes by performing quantum chemical calculations, where the methyl radical acts as the Lewis base and the σ-hole on the X atom in FXH3 as the Lewis acid. The interaction between the methyl radical and FXH3 is characterized by a red shift of F-X stretching frequency. The strength of the tetrel bond becomes stronger by not only increasing the atomic number of the central atom X (X = C, Si, Ge, and Sn) but also by enhancing the electron-withdrawing ability of substituents in the Lewis acid. The energy decomposition analysis highlights the importance of the electrostatic interaction in the formation of the tetrel bond, although the dispersion part is also non-negligible for the weak tetrel bond. There is a competition between the formation of single-electron tetrel bonds and hydrogen bonds for the complexes composed of the methyl radical and CNCH3 or NCCH3. Furthermore, the single-electron tetrel bond exhibits the cooperative effect not only with the hydrogen bond in the complex of NCH···NCCH3···CH3, but also with the conventional tetrel bond in NCCH3···NCCH3···CH3.

The inability to synthesize single-wall carbon nanotubes (SWCNTs) possessing uniform electronic properties and chirality represents the major impediment to their widespread applications. Recently, there is growing interest to explore and synthesize well-defined carbon nanostructures, including fullerenes, short nanotubes, and sidewalls of nanotubes, aiming for controlled synthesis of SWCNTs. One noticeable advantage of such processes is that no metal catalysts are used, and the produced nanotubes will be free of metal contamination. Many of these methods, however, suffer shortcomings of either low yield or poor controllability of nanotube uniformity. Here, we report a brand new approach to achieve high-efficiency metal-free growth of nearly pure SWCNT semiconductors, as supported by extensive spectroscopic characterization, electrical transport measurements, and density functional theory calculations. Our strategy combines bottom-up organic chemistry synthesis with vapor phase epitaxy elongation. We identify a strong correlation between the electronic properties of SWCNTs and their diameters in nanotube growth. This study not only provides material platforms for electronic applications of semiconducting SWCNTs but also contributes to fundamental understanding of the growth mechanism and controlled synthesis of SWCNTs.

production cost, simple processability, and remarkably high power conversion efficiency (PCE). [1][2][3][4] A great deal of research effort has been dedicated to the development of PSCs, including perovskite compositional engineering, advanced deposition techniques for the fabrication of high-quality perovskite films, device architecture design, and charge-selective layer optimization, as well as stability improvement etc. [5][6][7][8][9] In just a few years, the PCE of PSCs has been dramatically increased from the initial 3.8% to a certified value of over 23%, making them one of the most promising choices among low cost nextgeneration solar cell technologies. [10,11] In state-of-the-art PSCs, charge-selective contacts including hole-transporting materials (HTMs) and electron-transporting materials (ETMs) are indispensable components for achieving high PCE and high stability. [12][13][14] They play essential roles in extracting and collecting the photo-generated charge from the perovskite to the respective electrode, thus effectively reducing undesirable recombination losses at the interface and improving solar cell performance. To date, the most efficient PSCs typically utilize 2,2′,7,7′-tetrakis(N,N-di-pmethoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) Copper (II) phthalocyanines (CuPcs) have attracted growing interest as promising hole-transporting materials (HTMs) in perovskite solar cells (PSCs) due to their low-cost and excellent stability. However, the most efficient PSCs using CuPc-based HTMs reported thus far still rely on hygroscopic p-type dopants, which notoriously deteriorate device stability. Herein, two new CuPc derivatives are designed, namely CuPc-Bu and CuPc-OBu, by molecular engineering of the non-peripheral substituents of the Pc rings, and applied as dopant-free HTMs in PSCs. Remarkably, a small structural change from butyl groups to butoxy groups in the substituents of the Pc rings significantly influences the molecular ordering and effectively improves the hole mobility and solar cell performance. As a consequence, PSCs based on dopant-free CuPc-OBu as HTMs deliver an impressive power conversion efficiency (PCE) of up to 17.6% under one sun illumination, which is considerably higher than that of devices with CuPc-Bu (14.3%). Moreover, PSCs containing dopant-free CuPc-OBu HTMs show a markedly improved ambient stability when stored without encapsulation under ambient conditions with a relative humidity of 85% compared to devices containing doped Spiro-OMeTAD. This work thus provides a fundamental strategy for the future design of cost-effective and stable HTMs for PSCs and other optoelectronic devices.

The performance of polymer solar cells (PSCs) is commonly improved using additives or annealing treatment. However, these processes are accompanied by disadvantages, including poor reproducibility and stability. Herein, a molecular design strategy is proposed to obtain additive-and annealing-free PSCs. IDTOT2F containing two alkoxyl side chains at the central unit of the nonfullerene acceptor IDTT2F was developed. This molecular design results in excellent solubility in solutions, ordered molecular packing in films, slightly elevated energy levels, and a higher film absorption coefficient. Compared with its counterpart IDTT2F, its improved solubility provides an active layer with better morphology, its ordered molecular packing enhances the charge mobility in blend films, and its slightly elevated energy level furnishes a higher open-circuit voltage of devices. As a result, IDTOT2F-based devices display a maximum power conversion efficiency of 12.79%, which is one of the highest values reported for a PSC fabricated without any extra treatment.