ZnO layers doped with small molecule viologen derivatives, i.e., 1,1 0 -bis(4hydroxypropyl)-[4,4 0 -bipyridine]-1,1 0 -diium bromide (V─OH) or 1,1 0 -bis(2,3dihydroxypropyl)-[4,4 0 -bipyridine]-1,1 0 -diium bromide (V─2OH), are prepared and used as the electron transport layer in inverted polymer solar cells (iPSCs). The presence of V─OH (or V─2OH) in ZnO layer and the formation of homogeneous V─OH (or V─2OH) doped ZnO layer are confirmed by Xray photoelectron spectroscopy. The electron mobilities of doped ZnO layers are comparable to those of pristine ZnO because the crystallinity of the ZnO layer is not significantly affected by the doping process. Kelvin probe microscopy measurements show that the work function of doped ZnO layers is in the range of À4.2 -À4.3 eV, which is higher than that of pristine ZnO (À4.5 eV). This is due to the formation of interface dipoles at the interface between the ZnO layer and the active layer. The water contact angle data reflect the existence of quaternary ammonium bromide on the surface, and unreacted hydroxyl groups are pointed away from the surface of the ZnO layer. iPSCs based on V─OH doped ZnO and V─2OH doped ZnO exhibit power conversion efficiencies (PCEs) up to 9.0% and 8.6%, which are dramatically enhanced compared to the device based on pristine ZnO (PCE ¼ 7.4%).

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Two-dimensional transition-metal dichalcogenides (2D TMDs) such as molybdenum disulfide (MoS 2 ) have received great attention for various applications. However, large-scale synthesis of high-quality 2D TMDs remains a challenge. Atomic layer deposition (ALD) is a promising deposition method for synthesizing large-area 2D TMDs, but it shows poor film quality due to the narrow process temperature window caused by the low thermal stability of conventional precursors. In this study, a plasma-enhanced atomic layer deposition (PEALD) process utilizing a new cyclopentadienyl-based Mo precursor (r-cyclopentadienyl dicarbonyl nitrosyl molybdenum, IM-02) was presented for synthesizing crystalline MoS 2 at a low growth temperature. IM-02 exhibited excellent thermal stability and suitability as an ALD precursor. The resulting MoS 2 thin films showed good uniformity and crystallinity without additional thermal treatment. Interestingly, the quality of the MoS 2 film was further improved by exposure to H 2 S plasma, which increased crystallinity and reduced grain boundaries and surface defects, suppressing surface contamination by carbon and oxygen in air. The resulting MoS 2 thin films were highly selective for NO 2 gas, with a response rate of about 50% at 100 ppm NO 2 even at room temperature, indicating their potential for use in gas sensors. These results suggest the PEALD process using IM-02 and H 2 S plasma as a promising approach for synthesizing high-quality MoS 2 thin films, with potential applications in various fields.

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