Synthesis and characterization of Ni:ZnO thin ﬁlms as photoanode for planar perovskite solar cell R.K. Pandey * , Anjali Vaishnaw , Koushik Ghosh , Pratibha Xalxo , P.K. Bajpai Department of Pure and Applied Physics, Guru Ghasidas Vishwavidyalaya, Chhattisgarh-495009, India A R T I C L E INFO Keywords: Perovskite solar cells Sol-gel spin coating Semiconductor materials ZnO thin ﬁlms Electron Transport Layer (ETL) ABSTRACT Thin ﬁlms of Ni:ZnO were successfully synthesized by sol-gel spin coating system for 0.5 % and 2.5 % Ni doping concentration on FTO coated substrate. The synthesized ﬁlms were annealed at 540 ◦ C for 4 h. The annealed thin ﬁlms were characterized for its electrical, optical and chemical characteristics using UV–Vis, Micro Raman, and FTIR spectroscopy, respectively. The UV–Vis spectra analysis reveals that the energy band gap of deposited ﬁlms found to be 3.58 eV and 3.51 eV for 0.5 % and 2.5 % Ni:ZnO thin ﬁlms, respectively. Two signiﬁcant charac- teristic peaks identiﬁed at 424 cm  1 and 563 cm  1 in Raman spectra. These peaks are attributed to E high 2 and LO (A 1 and E 1 ) modes, which conﬁrms the hexagonal wurtzite phase of Ni:ZnO thin ﬁlms. Furthermore, the ab- sorption peaks observed at 530 cm  1 and 635 cm  1 in the FTIR spectra are attributed to the characteristic stretching vibrational modes of Zn-O and Ni-O bonds, respectively. 1. Introduction In light of the ﬁnite nature of fossil fuel reserves, concerns about climate change and the increasing demand of electricity there is an essential need to explore alternative sources of energy that would last much longer and reduce the dependency on fossil fuels [1]. Due to the broad accessibility, universal applicability, and environment friendly characteristics, solar energy stands out as the optimal choice among all alternative renewable energy sources [2]. The efforts are being made to convert the sun light into more usable form using various photovoltaic structures. Progress has been made in the area of renewable energy by developing technology related to speciﬁc design, optimization and ad- ditive engineering [3-7]. However, suitable structure, efﬁciency and stability are the main cause of concern yet to be crossed. In order to make integrated solar cells encapsulated into single cells more viable, long-lasting, stable and efﬁcient, essential efforts are needed to be made [8-10]. A key problem in the area of photovoltaic cell development is to achieve the highest possible efﬁciency at the lowest possible cost of production and the effective way to solve this problem is to reduce the internal losses of the cell [11]. Perovskites solar cells are third-generation solar cells have been proposed to address the loss mechanisms in an attempt to improve solar cell performance. There are several key points which highlight the growing importance of perovskite solar cells, are efﬁciency and performance, cost-effectiveness, ﬂexibility and versatility, environmental friendly, potential for tandem Solar Cells (fourth generation solar cell) etc. Compared to other existing perovskite technologies, dye-sensitized photovoltaic cells face challenges with temperature stability, poisonous and volatile substances [12]. Solar cells based on quantum dots exhibit high toxicity and degradation issues. Organic and polymeric photovoltaic cells suffer from low efﬁciency, while multi-junction solar cells are complex and expensive [13-15]. In this context, Metal halide perovskite materials are used for making signiﬁcant optoelectronic devices because of its long carrier diffusion length, high carrier mobility, high exciton binding energy, large ab- sorption coefﬁcient, high carrier density and low trap density. In pre- vious reports, perovskite solar cells (PSCs) is remarkably highlighted by the rapid increase in their power conversion efﬁciency (PCE), which has surged from 3 % to 25.2 % (and up to 28 % in tandem architectures) within just a decade. In comparison, other solar technologies required nearly 30 years to achieve a similar level of advancement [16,17]. In the conventional design of perovskite solar cells (PSCs), innova- tive hybrid organic-inorganic perovskite materials act as the absorbing layer positioned between the electron-transporting layer (ETL) and hole- transporting layer (HTL) [18]. Typically, the ETL comprise of various inorganic metal oxides such as TiO 2 , ZnO, NiO 2 , and other n-type organic or inorganic materials. These layers serve as the photoanode of the PSC and can be synthesized using diverse solution-based techniques. The transport layer in perovskite solar cells is vital for improving charge * Corresponding author. E-mail addresses: rkpandeyggv@gmail.com (R.K. Pandey), v.anjali0408@gmail.com (A. Vaishnaw). Contents lists available at ScienceDirect Solar Compass journal homepage: www.elsevier.com/locate/solcom https://doi.org/10.1016/j.solcom.2024.100084 Received 27 April 2024; Received in revised form 30 June 2024; Accepted 11 August 2024 Solar Compass 12 (2024) 100084 Available online 13 August 2024 2772-9400/© 2024 The Authors. Published by Elsevier Ltd on behalf of International Solar Alliance. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).