ABSTRACT
Environment friendly molecular precursors are extensively studied for green, economical and scalable fabrication of inorganic thin films for various device applications. For compound semiconductors such as the chalcogenide solar absorber Cu2ZnSnS4 (CZTS), the stability of such precursor solution is highly sought after. The longer shelf life of the precursor could significantly improve the phase purity as well as the reproducibility of the resulting films, and also would aid the industrial scaling up of the fabrication process. Herein, the reason behind the exceptional stability shown by a precursor solution for CZTS is explored, by probing the nature of interaction between its various components. The unique combination of solvent and the sulfur source is shown as favorable for the stable bonds in the solution, especially the predominant bidentate bridging of sulfur source to the metal atoms. The insights elucidated through simple spectroscopic techniques can be handy when designing such sustainable precursors for other functional chalcogenides and technologically important inorganic compounds.
ABSTRACT
Ultraviolet (UV) photodetectors are considered as the major players in energy saving technology of the future. Efforts are needed to further develop such devices, which are capable of operating efficiently at low driving potential as well as with weak illumination. Herein, we report an all-oxide, highly transparent TiO2/MoO3 bilayer film, with nanoparticulate anatase TiO2 as the platform, fabricated by a simple solution based method and demonstrate its use in UV photodetection. Photoconductivity measurement with 352 nm light reveals the self-powered UV detection capability of the device due to the built-in potential at the bilayer interface. The device exhibits a high photoresponsivity (46.05 A W-1), detectivity (2.84 × 1012 Jones) and EQE (16 223%) even with a weak illumination of 76 µW cm-2, at a low bias of only -1 V. The self-powered performance of the bilayer device is comparable to that of commercial Si photodetectors as well as other such UV detectors reported based on metal oxide heterojunctions. The improved and faster photoresponse shown by the device is due to the formation of an effective heterojunction, as evidenced by XPS, electrochemical and I-V studies. It can be further attributed to the better charge transport through the densely aligned nanostructures, reduced recombination and the better mobility of anatase TiO2 nanoparticles. The performance is best-in-class and proves the potential of the transparent heterojunction to be used in highly responsive, self-powered UV detectors for low bias, low light applications.
ABSTRACT
ZnO nanorods were capped with a simple amino acid, viz., l-alanine to increase the carrier concentration and improve the performance of ZnO/CuI heterojunction diodes. The effect of l-alanine capping on the morphology, structural, optical, electrochemical and electrical properties of ZnO nanorods had been studied in detail. The stable structure with two equally strong Zn-O coordinate bonds predicted by density functional theory was in agreement with the experimental results of FTIR spectroscopy. Due to the presence of electron-releasing (+I effect) moieties in l-Alanine, the carrier concentration of capped ZnO nanorods was two orders of magnitude higher and the ZnO/CuI heterojunction device showed more than a two-fold increase in the photovoltaic power conversion efficiency.
