ARTICLE Copyright © 2019 by American Scientific Publishers All rights reserved. Printed in the United States of America Journal of Nanoelectronics and Optoelectronics Vol. 14, pp. 1–5, 2019 www.aspbs.com/jno Nickel Oxide Monodispersed Quantum Dots as Hole Transport Layer in n–i –p Hybrid Perovskite Solar Cells Ashique Kota and Hyung-Kee Seo * In this work NiO monodispersed quantum dots (QDs) were synthesized by the reduction of nickel (II) acety- lacetonate with the borane–trimethylamine complex in a mixture of oleylamine, which acted as capping agent and helped to control the particle size growth. These were then used as a hole transport layer in regular (n–i–p) type organic–inorganic hybrid perovskite solar cells. Morphology of the NiO QDs was observed with Field emission electron microscope (FESEM) and high resolution transmission electron microscope (HR-TEM) that revealed a monodispersed particles of an average particle size of about 5.5 ± 0.5 nm with distinct lattice fringes (spacing of 0.24 nm). A solar cell was fabricated on FTO glass by coating compact TiO 2 , methylam- monium lead halide (MAPbI), NiO-QDs and gold electrode (FTO/c-TiO 2 /MAPbI/NiO/Au). With the fabricated cell, we were able to obtain photo-conversion efficiency of 6.2%, fill factor of 0. 56, J sc is 10.77 mA/cm 2 and V oc is 1.02 V, which is a reasonable value for such cells. Keywords: Methylammonium Lead Halide, Nickle Oxide, Solar Cell, Perovskite. 1. INTRODUCTION In a step further to progresses made on the use of perovskite materials (PM) especially for optoelectronics, organometal trihalide perovskites (OTPs) have emerged as new subclass of PM and sparked interest for detailed inves- tigation. The major attraction for researching such mate- rial has been the advantage of simple and low-temperature synthesis/processing, ease of adjusting bandgap values, large choice on compositions, and importantly superior charge transfer dynamics. In past literature survey has been filled with PM based solar cells wherein the con- version efficiency has been reported ranging from 3.8 to 21.6% [1–10]. With lots of challenges in tailoring the opto- electronic and physiochemical properties, researchers are making progress as well as further researches are required with emphasis on photovoltaic and piezoelectric applica- tions. This would require several strategies for synthe- sis of OTPs including use of different dopants, synthesis School of Chemical Engineering, Chonbuk National University, Jeonju 54896, Korea ∗ Author to whom correspondence should be addressed. Email: hkseo@jbnu.ac.kr Received: 11 January 2019 Accepted: 12 March 2019 techniques, processing conditions, layered structures, hole transport (HT) layers and so on. The impact of hole transport materials as an efficient hole extraction in perovskite solar cells (PVSCs) have been well reported leading to long term stability. For example, Liu et al. used thin film of nickel oxide (NiOx) via low- temperature solution-processing as a hole transport layer in (p–i–n) planar as well as regular (n–i–p) hybrid per- ovskite solar cells and reported about 10% increase in the fill factor and about 23% increase in short circuit current density [11]. Kwon et al. prepared a solution-based p–i–n-type planar-structured perovskite photovoltaic (PV) cells, with a hole transport layer of pre-crystallized NiO nanoparti- cles that resulted in an excellent energy-level alignment and improved electron-blocking capability, resulting in V oc of ∼0.13 V, FF of 74% and efficiency of 15.4%, rel- atively higher than the conventional PEDOT:PSS-based devices [12]. In another publication by Jeonggi Kim et al., a film based nanoparticles of NiOx, synthesized by solution method, was used as a hole injection layers to assess its effect on the properties and functionality of organic light- emitting diodes (OLEDs), wherein higher current, power efficiency values and external quantum efficiency values J. Nanoelectron. Optoelectron. 2019, Vol. 14, No. xx 1555-130X/2019/14/001/005 doi:10.1166/jno.2019.2660 1