Electrical and optical characteristics of solution-processed MoO x and ZnO QDs heterojunction
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Research Letter
Electrical and optical characteristics of solution-processed MoOx and ZnO QDs heterojunction Hemant Kumar, Yogesh Kumar, Gopal Rawat, and Chandan Kumar, Department of Electronics Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India Bratindranath Mukherjee, Department of Metallurgical Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India Bhola N. Pal, School of Material Science and Technology, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India Satyabrata Jit, Department of Electronics Engineering, Indian Institute of Technology (Banaras Hindu University), Varanasi 221005, India Address all correspondence to Hemant Kumar, Satyabrata Jit at [email protected], [email protected] (Received 3 June 2017; accepted 1 August 2017)
Abstract In this work, effects of heat treatment on the heterojunction between MoOx and ZnO quantum dots (QDs) are analyzed possibly for the first time. Solution-processed and thermal deposition technique is used for the growth of MoOx over the ZnO QDs and compared for the electrical analysis. The absorption and photoluminescence properties of ZnO QDs and MoOx have been analyzed for the optical behavior. Further, the heat-treated heterojunctions are analyzed for built-in potential (0.25 V), carrier density (∼2.9 × 1018 cm−3), and responsivity (3.93 mAW−1). The heterojunction of solution-processed MoOx and ZnO QDs shows better stability after heat treatment compared with other devices.
Introduction The role of charge transport layer is one of the most important parameters in the field of solar cells[1,2] and photodetectors.[3,4] Multiple materials are used as a charge transport layer among which ZnO,[4] TiO2,[4] Cs2CO3,[5] and Nb2O[56] are the mostly used as an electron transport layer (ETL).[2] While the materials such as PEDOT:PSS,[7,8] MoOx,[9] NiO,[10] WO3,[8] and V2O[511] are used as a hole transport layer (HTL). Wide and direct band gap metal–oxide semiconductors such as ZnO and TiO2 are the most viable option for ETL due to their inherent n-type nature, high transparency in the visible region, and suitability for widespread deposition techniques from physical to chemical deposition methods. However, the solution-based deposition technique is considered to be the most cost-effective and simplest method for large area nanoelectronics.[12] Furthermore, ZnO is widely investigated due to its low cost,[13] large abundance,[13,14] and consistent nature of being n-type, whereas TiO2 varies between semiconductor to insulator depending upon the phase of the TiO2 thin film or nanocrystal.[15–18] Similarly, MoOx is mostly preferred HTL[1,2] the involvement of MoOx layer as HTL provides greater air stability to the fabricated device structure compared with other HTL counterparts.[19] However, for the deposition of MoOx thin-film thermal evaporation is the most used technique.[2] MoOx deposited via thermal evaporation are very sensitive toward the temperature and det
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