Surface Modification of Aluminum Doped Zinc Oxide by Ozone-Gas Treatment for Perovskite Solar Cells
Arun Singh Chouhan a, Naga Prathibha Jasti a b, Sushobhan Avasthi a
a Indian Institute of Science, Bengaluru, IN, Bangalore, India
b Institute of Nanotechnology and Advanced Materials, Bar Ilan University, ISRAEL
nanoGe Perovskite Conferences
Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
International Conference on Perovskite Thin Film Photovoltaics
Jerusalem, Israel, 2019 February 24th - 27th
Organizers: Lioz Etgar and Kai Zhu
Oral, Arun Singh Chouhan, presentation 026
Publication date: 21st November 2018

Zinc oxide (ZnO) is a well-known electron transport layer (ETL) for efficient Organometal halide perovskite (CH3NH3PbI3) based solar cell with efficiency as high as 17.5% [1]. Over other ETL like TiO2, it has various advantages: higher electron mobility, easy to etch and ability to be doped. However, perovskite material deposited over ZnO suffers from chemical reaction at interface and fast degradation of perovskite material [2], which leads to less stable device. Interestingly, doping ZnO with aluminum i.e, aluminum doped zinc oxide (AZO) is found to be more suitable for perovskite solar cell, as the latter has more stable interface with perovskite [3], [4]. Also, AZO is highly-conductive (as low as 9 ohm/sq.) and transparent (> 80%), so it doubles up as the transparent conducting oxide (TCO) thus replacing hard-to-etch FTO and expensive ITO.

In this work, we present fabrication and device physics of AZO/Perovskite/HTL/Au stack, in which AZO has dual role: as TCO and ETL. AZO replacing the conventional FTO/c-TiO2/meso-TiO2 stack, simplifying the fabrication process and reduction in thermal budget. Combining results from Ultraviolet photoelectron spectroscopy (UPS) and UV-Visible spectroscopy (UV-Vis), suggests AZO will act as an effective ETL for perovskite thin-film, with a large valence-band offset and a small conduction-band offset. Constructed electronic band diagram provide the details of possible path for carrier recombination at the interface. Here, we have addressed this problem by ozone treating the surface of AZO (AZO:O3). Ozone-treated AZO interface yields planar CH3NH3PbI3 solar cells with significantly reduced hysteresis and open-circuit voltage (VOC) up to 1.05 V.

We show that AZO:O3 has better charge extraction as compared to AZO and hence a better ETL for perovskite solar cell. By exposing AZO to ozone-gas reduces the oxygen vacancies film (claim supported by O1s spectra of X-ray photoelectron spectroscopy) and hence doping in the 6-10 nm of the AZO thin-film. This gradient in n-type doping at the AZO surface creates electric field at the AZO surface and enhance charge extraction. Steady state photoluminescence (SSPL) was used to experimentally prove the conclusion.

As charge carrier recombination and extraction at the interfaces play a crucial role for device performance enhancement, we believe this controllable ozone treatment has a broader scope and can be a potential tool for various other oxides.   

This work is supported in part under the U.S.−India Partnership to Advance Clean Energy-Research (PACE-R) for the Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences, and Energy Efficiency and Renewable Energy, Solar Energy Technology Program, under Subcontract DE-AC36-08GO28308 to the National Renewable Energy Laboratory, Golden, Colorado) and the Government of India, through the Department of Science and Technology under Subcontract IUSSTF/JCERDC-SERIIUS/2012 dated 22nd Nov. 2012. The work is also supported by Department of Science and Technology (DST), Government of India, under project reference no: SB/S3/EECE/0163/2014. Authors would like to acknowledge the support of the National Nano Fabrication Center (NNfC) and Mico-Nano Characterization Facility (MNCF) for providing access to fabrication and characterization facilities. NNfC and MNCF are funded by a grant from the Ministry of Electronics and Information Technology (MeitY), Government of India. One of the authors acknowledges support from Young Faculty Research Fellowship under the “Visvesvaraya PhD Scheme for Electronics & IT” program by MeitY, Government of India.

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