Graphenetwo-dimensional (2D) sheets of carbon atoms linked in a honeycomb patternhas unique properties that exhibit great promise for various applications including solar cells. Herein we prepared two-dimensional (2D) reduced graphene oxide (rGO) nanosheets from naturally abundant graphite flakes (obtained from Tuv aimag in Mongolia) using solution processed chemical oxidation and thermal reduction methods. As a proof of concept, we used our rGO as a hole transporting material (HTM) in perovskite solar cells (PSCs). Promisingly, the use of rGO in the hole transporting layer (HTL) not only enhanced the photovoltaic efficiency of PSCs, but also improved the device stability. In particular, the best performing PSC employing rGO nanosheets exhibited a power conversion efficiency (PCE) of up to 18.13%, while the control device without rGO delivered a maximum efficiency of 17.26%. The present work demonstrates the possibilities for solving PSC issues (stability) using nanomaterials derived from naturally abundant graphite sources. Fig. 3 (a) Raman spectra of GO and rGO samples. (b) AFM image and (c) the corresponding height profile of rGO nanosheet. 9136 | RSC Adv., 2020, 10, 9133-9139 This journal is

According to International Energy Agency (IEA), no investment in new fossil fuel supply projects will be made from today, while there will be no sales of new internal combustion engine passenger cars by 2035. [2] Renewable energy sources such as wind and solar energy are capable of generating around 70% of global electricity demand by 2050. [2] Solar photovoltaic (PV) technologies are of particular interest because the sun is the world's largest source of energy supply.Impressively, solar cells made of silicon (Si) semiconductors provide a combination of excellent PV performance and a long lifetime. Their commercial modules can last for more than 20 years, and therefore, mono-and poly-crystalline Si solar cells make up >90% of the PV market. [3] Notably, recent progress in PV sector has led to a considerable reduction in the module price of Si solar cells, but the overall systems still suffer from high installation costs (known as balance of system) which are accountable for 75% of the system cost. [4] Therefore, further developments are still in demand in order to maximize Perovskite solar cells (PSCs) have attracted a great deal of attention from the photovoltaic (PV) community because of their remarkable performance, low production cost, and high potential to be integrated into other optoelectronic applications. Despite their promise, the challenges associated with their operational stability have drawn increasing attention over the past decade. Owing to their unique structure and fascinating properties such as high charge mobility, excellent conductivity, tunable bandgap, good optical transparency, and optimal surface functionalization, nanostructured materials, in particular monoelemental 2D materials, have recently been demonstrated to play versatile functions in suppressing the degradation of PSCs and enhancing the PV performance of the devices. In this review, recent advances in perovskite solar cells employing monoelemental 2D materials are presented. A brief overview of perovskite light absorbers based PV devices is first introduced, followed by critical discussions on the use of various elemental 2D materials including graphene, phosphorene, antimonene, borophene, bismuthene, and their derivatives for different components of the perovskite solar cells. Finally, the challenges in this cutting-edge research area are highlighted, and the authors express their own perspectives on addressing these key issues.

Research interest in two-dimensional (2D) materials has grown exponentially across various fields over the past few years. In particular, 2D phosphorene, the single- or few-layered analogue of semiconducting black phosphorus...