DOI: 10.1002/ijch.201400208 Improvement of a-Si:H Thin-film Solar Cells by Employing Large Ag Nanoparticles Sunhwa Lee, [a, b] Jinjoo Park, [b] Junsin Yi, [b, c] and Chaehwan Jeong* [a] 1. Introduction Thin-film silicon solar cells have been recognized as cost- effective devices for various applications, for their flexi- bility, light weight, and potential for use in integrated photovoltaic (BIPV) systems. However, there are some known limitations regarding efficiency, due to degrada- tion of silicon material and difficulty in light trapping. In silicon-wafer-based solar cells, a surface texture with pyr- amid shapes around 10 mm in size can be a versatile method for the improvement of light trapping. But this method cannot be used in thin-film silicon solar cells be- cause of damage to the thin layer. Recently, many researchers have suggested various methods for the improvement of light trapping, such as the application of nanocones, [1,2] nanorods, [3–5] nano- wires, [6–8] and nanoparticles. [9] Compared with convention- ally structured thin films, planar-type silicon devices, these nanostructured devices have excellent enhanced charge collection and improved light absorption. Nano- structured devices with arrays of a novel metal can have strong light trapping because strong light-matter interac- tion in metal nanoparticles enables large scattering cross sections. [10,11] This phenomenon is known as the plasmonic effect, and results from the strong coupling of electro- magnetic waves. The nanoparticle response caused by the dipole oscillation of localized surface plasmons serves to increase the local electromagnetic field near the nanopar- ticles at the surface plasmon resonance, as well as to en- hance the scattering cross section for off-resonant light. [11] Recently, a few reports have been published using Au metal nanoparticles, with efficiency of ~ 2–3 %, as report- ed by Derkacs et al. [12] Small Au metal nanoparticles of below 100 nm were used for their light-trapping effect, re- sulting in increased metallic losses by various phenomena, such as absorption, weak scattering, and interference be- tween the incident light and the metal medium. In this work, a-Si:H solar cells were fabricated by form- ing relatively large Ag nanoparticles on FTO-coated glass. Light can be preferentially scattered and trapped in the absorber layer by multiple and high-angle scattering. Optical properties, such as transmittance, absorption, re- flectance, and haze ratio, were investigated with different RMS roughness of Ag nanoparticles on FTO-coated glass and also on FTO-coated glass without Ag nanoparticles. The electrical properties of intrinsic layers were also stud- ied with different roughness of the Ag nanoparticles. Abstract : Silver (Ag) nanoparticles were formed on fluorine- doped tin oxide (FTO) coated glass substrate, and then hy- drogenated amorphous silicon (a-Si:H) thin-film solar cells were sequentially fabricated. Ag nanoparticles located in the interface between the FTO and the p-layer leads to a light- trapping effect because of the strong light-material interac- tion in Ag nanoparticles and enhancement of the optical path length. A higher haze ratio appeared for Ag nanoparti- cles with larger diameters and heights, compared with the conventional type. The device with the Ag nanoparticles showed a short-circuit current density of 12.66 mA cm 2 , which was 2.2 mA cm 2 higher than the device without Ag nanoparticles. Conversion efficiency increased from 4.9 % to 5.9 % by employing Ag nanoparticles with a roughness of 71 nm. The simple process makes our design useful for low- cost, high conversion efficiency thin-film solar cells. Keywords: light trapping · nanoparticles · plasmonic · silver · thin-film solar cells [a] S. Lee, C. Jeong Applied Optics and Energy Research Group Korea Institute of Industrial Technology Gwangju 506-824 (Republic of Korea) Tel.: (+ 82) 62-6006-380 Fax: (+ 82) 62-6006-719 e-mail: chjeong@kitech.re.kr [b] S. Lee, J. Park, J. Yi School of Information and Communication Engineering Sungkyunkwan University Suwon 440-746 (Republic of Korea) [c] J. Yi Department of Energy Science Sungkyunkwan University Suwon 440-746 (Republic of Korea) Isr. J. Chem. 2015, 55, 1103 – 1108 # 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1103 Full Paper