Current Alternative Energy   Send Orders for Reprints to reprints@benthamscience.net Current Alternative Energy, 2019, 3, 3-17 3 REVIEW ARTICLE Recent Progress in Solar Cell Technology for Low-Light Indoor Applica- tions 2405-464X/19 $58.00+.00 © 2019 Bentham Science Publishers Soyeon Kim 1 , Muhammad Jahandar 1 , Jae Hoon Jeong 1 and Dong Chan Lim 1,* 1 Surface Technology Division, Materials Center for Energy Convergence, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea Abstract: Photovoltaic cells have recently attracted considerable attention for indoor energy harvest- ing for low-power-consumption electronic products due to the rapid growth of the Internet of Things (IoT). The IoT platform is being developed with a vision of connecting a variety of wireless electron- ic devices, such as sensors, household products, and personal data storage devices, which will be able to sense and communicate with their internal states or the external environment. A self-sustainable power source is required to power such devices under low light indoor environments. Inorganic pho- tovoltaic cells show excellent device performance under 1 Sun illumination and dominate the market for outdoor applications. However, their performance is limited for indoor applications with low in- cident light intensities as they exhibit low photo-voltage. Among the emerging photovoltaic technol- ogies, organic photovoltaics have unique advantages, including solution processibility, flexibility, and lightweight tailorable design; hence, they are considered the best solution for indoor light har- vesting applications due to their high photo-voltage, strong absorption of UV-visible wavelengths, and a spectral response similar to that emitted by modern indoor lighting systems. In this review arti- cle, we discuss the factors affecting device performance of different photovoltaic technologies under low incident light intensities or indoor conditions and provide a comprehensive analysis of future op- portunities for enhancing indoor performance of the photovoltaic devices. Furthermore, we discuss some of the results of semi-transparent organic solar cell which is operated under complex environ- mental conditions like low illumination, incident light angle etc. Based on the results, one can sug- gest that semi-transparent organic solar cell is more suitable for progressive indoor solar cell. After highlighting the factors that limit indoor device performance of photovoltaic cells, we discuss poten- tial applications of IoT devices powered by organic photovoltaic cells in indoor lighting environ- ments. A R T I C L E H I S T O R Y Received: October 10, 2018 Revised: December 04, 2018 Accepted: December 21, 2018 DOI: 10.2174/1570180816666190112141857 Keywords: Indoor lights, indoor photovoltaics, IoT, low-light intensity, photovoltaics, transparent OPV. 1. INTRODUCTION As society moves towards renewable energy sources in order to decarbonize electric power generation, Photovoltaic (PV) technologies are expected to play an important role. The continuous research and development of high-efficiency, low-cost, and solution-processible PV technologies can pro- vide an infinite source of energy and novel opportunities to exploit PV in energy harvesting applications from low-light intensity/indoor environments [1-13]. In such applications, solar cell devices need to operate under very different condi- tions than those experienced outdoors, e.g., light illumination intensities that are typically 10-1000 times lower than direct *Address correspondence to this author at the Surface Technology Division, Materials Center for Energy Convergence, Korea Institute of Materials Science (KIMS), Changwon 51508, Republic of Korea; Tel/Fax: +82-55-280-3511, +82-55-280-3570; E-mail: dclim@kims.re.kr sunlight, different orientations, and different light source spectra [2, 5, 7, 10]. The development of a light-harvesting technology that provides significant output power under low- light intensity and indoor environments has great prospects for applications in the field of domestic and building man- agement systems. Energy harvesting under low-light intensi- ty or indoor conditions has attracted considerable attention due to the unique requirements of the Internet of Things (IoT). The IoT concept promises a future where a wide varie- ty of devices, such as consumer electronics, sensors, house- hold products, and personal data storage devices will be con- nected through the internet and will be able to sense and communicate with their internal states or the external envi- ronment. Such devices will be integrated with wireless communication systems and are expected to be independent of the electric grid, so self-powered systems are essential [14-18].