Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Toward development of high-performance perovskite solar cells based on CH 3 NH 3 GeI 3 using computational approach Ahmed-Ali Kanoun a, ⁎ , Mohammed Benali Kanoun b, ⁎⁎ , Abdelkrim E. Merad a , Souraya Goumri-Said c a Equipe: Physique de l’Etat Solide, Laboratoire de Physique Théorique, Département de Physique, Faculté des Sciences, Université de Tlemcen, B.P. 119, 13000, Algeria b Physics Department, College of Science, King Faisal University, P.O. Box 400, Al-Ahsa 31982, Saudi Arabia c College of Science, Department of Physics, Alfaisal University, P.O. Box 50927, Riyadh 11533, Saudi Arabia ARTICLE INFO Keywords: Perovskite solar cells Hole transport material (HTM) SCAPS ABSTRACT We reported numerical simulations of device performances made of methylammonium germanium halide (CH 3 NH 3 GeI 3 )-based perovskite solar cells. The main goal here is to seek for an efficient method to improve the device efficiency of alternative lead-free perovskite based on germanium solar cells by using various organic and inorganic hole transport materials. For that aspiration, the effect of several parameters on the solar cell per- formance were investigated such as thicknesses of perovskite, HTM, defect density, hole mobility, and metal electrode work function on the charge collection. The device simulation revealed that the optimum thickness of CH 3 NH 3 GeI 3 absorber is found around 600 nm. Furthermore, Ge-based perovskite solar cells with Cu 2 O and D- PBTTT-14 as HTM exhibited a remarkable overall power conversion efficiency reaching 21%. The defect density reduction is a critical factor to improve the solar cell performance and should be controlled under the order of ∼10 15 cm 3 . Further simulations were performed to study the effect of operating temperature on the perfor- mance. Our simulation results advocate for a viable route to design hole-transporting materials for highly ef- ficient and stable perovskite solar cells with low cost. 1. Introduction Recently, solar cells based on composites of organic-inorganic hy- brid perovskite solar cells (PSCs) have received worldwide attention to their outstanding properties as super high absorption coefficients, re- latively high carrier mobility, long carrier lifetime simple fabrication process (Bi et al., 2016; Zhang et al., 2016; Kojima et al., 2009; Xing et al., 2013; Bakr et al., 2017). The power conversion efficiency (PCE) of perovskite based on photovoltaic devices has been greatly boosted from the 3.8% to over than 21.1% (Kojima et al., 2009; Zhang et al., 2017; Yang et al., 2015; Saliba et al., 2016a, 2016b; Li et al., 2016; Zhao et al., 2016; Shin et al., 2017). This value is comparable to the efficiencies of traditional commercial devices based on silicon of 20%, CIGS of 19.6%, GaAs of 18.4% and CdTe of 19.6% (Green et al., 2014; Goetzberger et al., 2003). Moreover, hybrid organic–inorganic per- ovskites are not only used for photovoltaic applications but they can be applied to other optoelectronic applications such as light-emitting diodes (LEDs) (Tan et al., 2014; Kim et al., 2015; Yu et al., 2015), photodetectors (Dou et al., 2014) and photodiodes (Lee et al., 2015; Lin et al., 2015). Highly efficient perovskite solar cells are composed of perovskite materials that have an ABX 3 structure, where A is a mono- valent organic cation (e.g. methylammonium (CH 3 NH 3 , MA), B is an inorganic metal cation (Pb, Sn) and the X-site is occupied by halide anion (X = Cl, Br, I). In spite of the positive aspect, and great progress made on lead halide perovskite material, its instability and toxicity may handicap its potential use and its large-scale commercial production (Conings et al., 2015; Sun et al., 2016). Thus, the serious environmental complications of lead require to seek for an alternative candidate eco- logic hybrid perovskite materials achieving the same high efficiency. The hybrid organic–inorganic Ge based perovskite may show analogous photovoltaic performance similar to Pb and Sn based perovskite devices as the element germanium belongs to the same subgroup with lead and tin (Hu et al., 2017; Saparov and Mitzi, 2016). In this perspective, the first time was synthesized of that of the halide perovskite CH 3 NH 3 Gel 3 by Stoumpos et al. (2013) discovering strong nonlinear optical prop- erties and highly distorted structure. Later in 2015, Krishnamoorthy et al. (2015) synthesized the lead-free germanium iodide perovskite materials, demonstrating a strong potential in photovoltaic https://doi.org/10.1016/j.solener.2019.02.041 Received 5 June 2018; Received in revised form 11 February 2019; Accepted 18 February 2019 ⁎ Corresponding author. ⁎⁎ Corresponding author. E-mail addresses: kanounahmedali13@gmail.com (A.-A. Kanoun), mkanoun@kfu.edu.sa (M.B. Kanoun), k_merad@mail.univ-tlemcen.dz (A.E. Merad). Solar Energy 182 (2019) 237–244 0038-092X/ © 2019 International Solar Energy Society. Published by Elsevier Ltd. All rights reserved. T