IP: 127.0.0.1 On: Fri, 17 May 2019 19:52:19 Copyright: American Scientific Publishers Delivered by Ingenta Copyright © 2019 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 19, 6601–6608, 2019 www.aspbs.com/jnn Defect Analysis of Solution-Based Process CIGS Thin-Film Solar Cells Using Technology Computer-Aided Design Sangah Lee 1 , Jaesung Lee 1 , Yoojeong Lee 1 , Gi Soon Park 2 , Min Kyu Kim 2 , Byung Koun Min 2 , and Myunghun Shin 1 ∗ 1 School of Electronics and Information Engineering, Korea Aerospace University, Goyang-City, Gyeonggi-do 412-791, Republic of Korea 2 Clean Energy Research Center, Korea Institute of Science and Technology, Hwarang-ro 14-gil 5, Seongbuk-gu, Seoul, 02792, Republic of Korea Copper indium gallium sulfur selenide (Cu(In 1-x Ga x SeS, CIGS) thin film solar cells are fabricated using a solution-based process, and their defect models are studied through a computer-aided design method. Cu(In 1-x Ga x SeS is structured with a graded bandgap by controlling the ambient gas and precursor composition, during the fabrication process. The defects in the CIGS are mod- eled as two donor-like defects, which are differently distributed as per the CIGS grain size (large and small grains at upper and bottom layers, respectively), whereas those in the cadmium sulfide (CdS)/CIGS interface are modeled as a complex model of both donor- and acceptor-like defects in the CdS, near the interface. By measuring the external quantum efficiency and current density– voltage characteristics, the best-fitting match of the simulated values with the measured values are obtained. The simulation results demonstrate that the defects (defect density of ∼7 × 10 18 ) in the CdS interface are more serious, compared to the CIGS defects (defect density of ∼2 × 10 15 in the bottom), which were initially expected to be more severe because of grain nonuniformity. For increasing the cell efficiency, we establish that the process and material quality need to be further improved not only during CIGS formation using a multistep spin-coated precursor but also during the initial deposition of the CdS buffer. This numerical approach can enable better understanding of the defect behavior in solar cells, and indicate directions for improvement in the fabrication process and device structure, for developing high-efficiency solution-based CIGS solar cells. Keywords: CIGS Solar Cell, Solution-Based Process, TCAD Simulation, Defect Modeling. 1. INTRODUCTION Thin-film photovoltaics have been extensively studied because of their many advantages, including the very low usage of raw materials and low-cost process depositing semiconductor materials directly on large-size glass or metal substrates. In addition, flexible solar cells, which can only be fabricated using thin-film technologies, are in the spotlight as next generation solar cells [1–3]. One such solar cell is the copper indium gallium sulfur selenide (Cu(In 1-x Ga x SeS, CIGS) solar cell, which is inorganic, thermally stable, and durable for long-term operation under light exposure, and has a high light absorption ∗ Author to whom correspondence should be addressed. coefficient for thin-film solar cells. The bandgap of its absorption layer can be easily tuned by controlling the composition ratio of indium and gallium [4–9]. In recent years, CIGS thin-film solar cells fabricated using a solution process have attracted attention because low-cost, high-throughput production on a large scale is expected to be possible, in contrast to the conventional vacuum deposition method [10–16]. However, for com- peting with CIGS solar cells fabricated using the vacuum deposition process, solution-based CIGS solar cells need to improve their efficiency. The low efficiency is mainly due to nonuniform material composition and small grain- size resulting from the currently used immature solution- based process for fabricating CIGS solar cells [16–19]. J. Nanosci. Nanotechnol. 2019, Vol. 19, No. 10 1533-4880/2019/19/6601/008 doi:10.1166/jnn.2019.17080 6601