Citation: Gulomov, J.; Accouche, O.; Aliev, R.; Neji, B.; Ghandour, R.; Gulomova, I.; Azab, M. Geometric Optimization of Perovskite Solar Cells with Metal Oxide Charge Transport Layers. Nanomaterials 2022, 12, 2692. https://doi.org/10.3390/ nano12152692 Academic Editor: Bo-Tau Liu Received: 11 July 2022 Accepted: 4 August 2022 Published: 5 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). nanomaterials Article Geometric Optimization of Perovskite Solar Cells with Metal Oxide Charge Transport Layers Jasurbek Gulomov 1,2, * , Oussama Accouche 3 , Rayimjon Aliev 1 , Bilel Neji 3 , Raymond Ghandour 3 , Irodakhon Gulomova 1 and Marc Azab 3, * 1 Renewable Energy Sources Laboratory, Andijan State University, Andijan 170100, Uzbekistan 2 Andijan State Pedagogical Institute, Andijan 170100, Uzbekistan 3 College of Engineering and Technology, American University of the Middle East, Egaila 54200, Kuwait * Correspondence: jasurbekgulomov@yahoo.com (J.G.); marc.azab@aum.edu.kw (M.A.) Abstract: Perovskite solar cells (PSCs) are a promising area of research among different new gen- erations of photovoltaic technologies. Their manufacturing costs make them appealing in the PV industry compared to their alternatives. Although PSCs offer high efficiency in thin layers, they are still in the development phase. Hence, optimizing the thickness of each of their layers is a challenging research area. In this paper, we investigate the effect of the thickness of each layer on the photoelectric parameters of n-ZnO/p-CH 3 NH 3 PbI 3 /p-NiO x solar cell through various simulations. Using the Sol–Gel method, PSC structure can be formed in different thicknesses. Our aim is to identify a functional connection between those thicknesses and the optimum open-circuit voltage and short-circuit cur- rent. Simulation results show that the maximum efficiency is obtained using a perovskite layer thickness of 200 nm, an electronic transport layer (ETL) thickness of 60 nm, and a hole transport layer (HTL) thickness of 20 nm. Furthermore, the output power, fill factor, open-circuit voltage, and short-circuit current of this structure are 18.9 mW/cm 2 , 76.94%, 1.188 V, and 20.677 mA/cm 2 , respectively. The maximum open-circuit voltage achieved by a solar cell with perovskite, ETL and HTL layer thicknesses of (200 nm, 60 nm, and 60 nm) is 1.2 V. On the other hand, solar cells with the following thicknesses, 800 nm, 80 nm, and 40 nm, and 600 nm, 80 nm, and 80 nm, achieved a maximum short-circuit current density of 21.46 mA/cm 2 and a fill factor of 83.35%. As a result, the maximum value of each of the photoelectric parameters is found in structures of different thicknesses. These encouraging results are another step further in the design and manufacturing journey of PSCs as a promising alternative to silicon PV. Keywords: photovoltaics; perovskite; metal oxide; solar cell; Sentaurus TCAD; photoelectric parameters; electron transport layer; hole transport layer 1. Introduction The race towards a completely sustainable, green, and zero-emission electricity has led to many challenges on various levels, especially at the end of energy production. While hydropower production is still leading the way as primary renewable-energy resource, solar-energy production is showing a strong and an exponential growth, from 30 TWh to more than 1000 TWh, during the last 10 years, according to our world in data [1]. This boost is steered with political supports and tax initiatives in many countries. Nowadays, numerous ongoing researches are being conducted to develop sustainable solar cells that are inexpensive, efficient, and with scalable production. On the industrial level, 95% of solar cells are made of silicon [2], offering a maximum efficiency of 29% [3], with costly processes when compared to the production processes of non-silicon-based solar cells [4]. This resulted in the exploration of new easy-to-synthesize materials to create sustainable and highly efficient solar cells by researchers [5]. The first perovskite solar cell was invented in 2009 with an efficiency of 3.8% [6]. In fact, the perovskite material can be synthesized using the Sol–Gel method, which is a Nanomaterials 2022, 12, 2692. https://doi.org/10.3390/nano12152692 https://www.mdpi.com/journal/nanomaterials