IEEE JOURNAL OF PHOTOVOLTAICS, VOL. 5, NO. 5, SEPTEMBER 2015 1373 Improving the Short-Wavelength Spectral Response of Silicon Solar Cells by Spray Deposition of YVO 4 : Eu 3+ Downshifting Phosphor Nanoparticles Nikhil Chander, Sanjay K. Sardana, Piyush K. Parashar, A. F. Khan, Santa Chawla, and Vamsi K. Komarala Abstract—Europium-doped yttrium vanadate downshifting phosphor nanoparticles (NPs) have been coated on top of monocrystalline silicon solar cells, having efficiency more than 15%, by a spray deposition technique. The effects of phosphor NPs on solar cells with antireflection coating (ARC) have been studied. The optimized quantity of phosphor NPs provides a pho- tocurrent enhancement of ∼2.1% for monosilicon solar cells. Ex- ternal quantum efficiency data of high-efficiency ARC layer-coated silicon solar cells conclusively show that the enhancement in short- wavelength spectral response is mainly due to downshifting effects of the phosphor NPs. A small increment in a long-wavelength spec- tral response is also observed due to the scattering effects of phos- phor NPs, which also results in a small enhancement of effective diffusion length of minority carriers in the base region. Index Terms—Downshifting, phosphor nanoparticles, silicon solar cell, spray deposition. I. INTRODUCTION D ESPITE the emergence of new materials, silicon solar cell technology is the market leader in the photovoltaics (PV) industry, and production line efficiencies have reached up to ∼19.5% and ∼18% for monocrystalline (mono-Si) and multicrystalline devices, respectively, [1], [2]. Modern con- cepts, like plasmonics, up-conversion (UC), and downshift- ing/conversion are presently in research stage to further enhance the efficiency of solar cells [3]–[7]. Photocurrent enhancement by UC of near-infrared (NIR) light to visible region has been demonstrated under concentrated sunlight for silicon solar cells [5], [6]. Luminescent downshifting (LDS) is another approach for en- hancing the silicon solar cell efficiency by improving its short- wavelength spectral response [7]–[9]. Silicon solar cells exhibit Manuscript received January 19, 2015; revised April 28, 2015; accepted May 25, 2015. Date of publication June 10, 2015; date of current version August 18, 2015. N. Chander, S. K. Sardana, P. K. Parashar, and V. K. Komarala are with the Photovoltaic Laboratory, Centre for Energy Studies, Indian Institute of Tech- nology Delhi, New Delhi 110016, India (e-mail: nikhilphysics@gmail.com; sanjay84sardana@gmail.com; piyushiitd11@gmail.com; vamsi@ces.iitd. ac.in). A. F. Khan is with the Department of Electronics and Information Technology, Ministry of Communications and Information Technology, New Delhi 110003, India (e-mail: khanafk@gmail.com). S. Chawla is with the Luminescent Materials Group, National Physical Lab- oratory, Council of Scientific and Industrial Research, New Delhi 110012, India (e-mail: santa@mail.nplindia.org). This paper has supplementary downloadable material available at http:// ieeexplore.ieee.org, provided by the authors. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JPHOTOV.2015.2438633 Fig. 1. Schematic of the textured surface of silicon solar cell covered with downshifting phosphor nanoparticles. relatively lower spectral response in the ultraviolet (UV)-blue (300–450 nm) region because of fast surface recombination of charge carriers and high optical reflectance [8]. These losses can be mitigated by using a suitable LDS material, which downshifts a portion of the incident high-energy UV photons to visible re- gion, where solar cell has optimum spectral response. The LDS materials have been used for improving the efficiency and stabil- ity of various types of devices, like silicon, CdTe, dye-sensitized, and perovskite solar cells [7]–[11]. In this study, we demonstrate the use of YVO 4 :Eu 3+ phosphor NPs synthesized via a chemical coprecipitation (CCP) method for enhancing the short-wavelength spectral response of high- efficiency (η> 15%) monosilicon solar cells with an antireflec- tion coating (ARC). Yttrium vanadate (YVO 4 ) host is the most widely used among rare earth vanadates, because of its high luminescent efficiency, thermal stability, and mechanical stur- diness [12]. Europium (Eu 3+ )-doped YVO 4 is an excellent can- didate for making efficient UV downshifting phosphors, since this compound has unique electronic and optical properties due to its specific 4f electronic structure [13]–[16]. An industrially viable, fast, and easy to implement spray deposition technique has been used for uniform coating of phosphor NPs directly on top of silicon solar cells. We also demonstrate the suitability of spray technique for depositing uniform films on solar cells of area ∼14 cm 2 . A schematic of textured surface of silicon solar cell covered with YVO 4 :Eu 3+ phosphor NPs is shown in Fig. 1. II. MATERIALS AND METHODS A. Cell fabrication The monosilicon solar cells used in this study were pro- cured from Bharat Heavy Electricals Limited (BHEL), India. The cells were cut into smaller pieces by a laser cutting process. 2156-3381 © 2015 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.