Abstract:We fabricated cantilevers for magnetic force microscopy with carbon nanotube tips coated with magnetic material. Images of a custom hard drive demonstrated 20 nm lateral resolution, with prospects for further improvements.

To date, the most efficient perovskite solar cells (PSCs) require hole‐transporting materials (HTMs) that are doped with hygroscopic additives to improve their performance. Unfortunately, such dopants negatively impact the overall PSCs stability and add cost and complexity to the device fabrication. Hence, there is a need to investigate new strategies to boost the typically modest performance of dopant‐free HTMs for efficient and stable PSCs. Thionation is a simple and single‐step approach to enhance the carrier‐transport capability of organic semiconductors, yet still completely unexplored in the context of HTMs for PSCs. In this work, a novel polymeric semiconductor, P1, based on a diketopyrrolopyrrole (DPP) moiety, is proposed as a dopant‐free HTM. Its modest performance in PSCs (power conversion efficiency (PCE) = 7.1%) is significantly enhanced upon thionation of the DPP moiety. The resulting dithioketopyrrolopyrrole‐based HTM, P2, leads to PSCs with nearly 40% performance improvement (PCE = 9.7%) compared to devices based on the nonthionated HTM (P1). Furthermore, thionation also remarkably boosts the shelf‐storage and thermal stability with respect to traditional 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene‐based PSCs. This work provides useful insights to further design effective dopant‐free HTMs employing the straightforward one‐step thionation strategy for efficient and stable PSCs.

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The integration of a functional group into dopant‐free hole‐transport materials (HTMs) to modify the perovskite|HTM interface has become a promising strategy for high‐performance and stable perovskite solar cells (PSCs). In this work, a sulfonated phenothiazine‐based HTM is reported, namely TAS, which consists of a butterfly structure with a readily synthesized N,​N‐​bis[4‐​(methylthio)​phenyl]​aniline side functional group. The interaction between TAS and perovskite via Pb–S bond induces a dipole moment that deepens the valence band of perovskite and thereby leads to enhanced open‐circuit voltage in corresponding n‐i‐p PSCs. More importantly, the functionalization of perovskite surface via Pb–S bond promotes the hole extraction reaction while suppressing the interfacial non‐radiative recombination, contributing to a 20–50% performance improvement compared to less‐ (4‐​(methylthio)​‐​N‐​[4‐​(methylthio)​phenyl]​aniline, DAS) or non‐interacting (N,N‐bis(4‐methoxyphenyl)aniline, TAO) counterparts. Consequently, TAS‐based PSCs exhibit superior device stability with a high PCE retention (>90% of the initial value) after 125 days of storage in the air.

We demonstrate the ability to straighten and align metal-coated carbon nanotubes with a focused ion beam. The metal-coated nanotubes align toward the source of the ion beam allowing their orientation to be changed at precise angles. By this technique, metal-coated nanotube tips that are several micrometers in length are prepared for scanning probe microscopy. We image high-aspect-ratio structures on the surface of a cell using these tips.