applied sciences Article  
Ambient Light Energy Harvesting and Numerical Modeling of Non-Linear Phenomena  
[PERSON]  
Department of Mechatronics Engineering, National University of Sciences and Technology, Islamabad 25120, Pakistan; [PERSON]L_ADDRESS]om  
Tailyeong Jeong2  
School of Artificial Intelligence Convergence, Hallym University, Chuncheon 24252, Korea  
Correspondence: [EMAIL_ADDRESS] or [EMAIL_ADDRESS]  
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to charge a smartphone and IoT devices inside a room. Similarly, a charging system using a light beam is presented in [PERSON] et al. [10]. An idea for smartphone charging using photovoltaics is suggested in [PERSON] et al. [11]. A study and an experiment are performed in [PERSON] et al. [12] for extending smartphone battery life using GaAs solar panels. In [PERSON] et al. [4, 7], different issues related to charging smartphones using light energy are discussed. The challenges and prospects of solar energy harvesting for IoT devices are discussed in [PERSON] et al. [13, 14]. The integration of in situ battery storage in solar modules and charging is discussed in [PERSON] et al. [15]. Devices are commercially available to externally charge the batteries of mobile phones using photovoltaic (PV) cells [4, 16, 17, 18]. These rechargers are external; they need to be carried at all times. Currently available commercialized energy harvesters use the additional battery as an energy bank, which occupies excessive space. The larger the photovoltaic cell area, the higher the harvested power, and a higher capacity battery is required to store this high energy. The solar energy harvesting charging system needs to efficiently work in both indoor and outdoor environments. Outdoor sunlight intensity is much higher than indoor artificial lights [19, 20]. The spectral, intensity, and power information of indoor lighting conditions are discussed in [PERSON] et al. [21, 22, 23]. To make PV energy harvesting feasible, large sized cells are required, such as 16 PV cells of 31 \(\times\) 31 \(\times\) 3.0 mm\({}^{3}\) as used by [PERSON] et al. [24]. In [PERSON] et al. [25] a flexible solar cell coupled with a supercapacitor was presented, which can be utilized in IoT devices. An ultrathin GaAs solar cell with a broadband absorption range and 19.9% efficiency was developed in [PERSON] et al. [26]. Solar cells for indoor IoT applications are discussed in [PERSON] et al. [27, 28]. In [PERSON] et al. [29] a flexible solar cell for outdoor applications of wireless sensor nodes was demonstrated. Dye-sensitized solar cells for indoor IoT applications are discussed in [PERSON] et al. [30, 31]. Research and approaches to flexible and wearable solar cells are mentioned in [PERSON] et al. [32]. Flexible and stretchable solar cells are discussed in [PERSON] et al. [33]. The prospects of thin-film, wide-bandgap halide perovskites, and metal/oxide/metal-based, organic, and perovskite solar energy harvesters for indoor IoT devices are promising, but challenges still exist [34, 35, 36, 37, 38]. The selection of photovoltaics depends on the incident light wavelength. Indoor lights are designed in the human visible range, while the sunlight spectrum at ground level is vast. The performance and selection of PV materials for both conditions make a choice complicated [39]. The most commonly used solar cells outdoors are polycrystalline. For indoor light energy harvesting, PV material amorphous silicon (which suits more ambient lighting, low efficiency 3-7%) and mono-crystalline (which is suited for direct incandescent and fluorescent lighting) are used, and these materials are efficient at different light intensities.