Indoor Organic Photovoltaics: Optimal Cell Design Principles with Synergistic Parasitic Resistance and Optical Modulation Effect

Abstract

Recently, the growing popularity of indoor electronic devices has led to considerable attention on ambient energy harvesting systems. In particular, the incorporation of electronic products that harness the Internet of Things (IoT) services has spurred interest in semipermanent indoor power generation systems, owing to their numerous sensor nodes. [1][2][3][4][5] Ambient energies such as light and heat and the conversion systems to turn them into electricity have been vigorously investigated for practical applications. Among them, indoor light energy and photovoltaic (PV) systems have shown potential for harvesting ambient energy, considering the high accessibility of the pertinent energy sources as well as the excellent power conversion capabilities of the PV system. [6][7][8][9][10][11][12] PV systems could incorporate different types of light-absorbing materials such as silicon, gallium arsenide, and organics. Organic photovoltaics (OPVs) is most suited for indoor energy harvesters, since their unique optical properties (such as high absorption coefficient and bandgap tunability) and other features (such as superior mechanical flexibility and diverse color options) could well match the indoor light conditions/environments characterized by low light intensity, varying output spectra, and aesthetic considerations. [13][14][15][16][17][18][19] Many studies tried to enhance the performance of OPVs under altered light conditions as opposed to outdoor conditions (1 sun) (more in detail will be discussed later). [20][21][22][23][24] As a result, substantial progress has been made, with the power conversion efficiency (PCE) up to 28% [25] with a 1000 lx fluorescent (FL) lamp and 30.8% with a 1650 lx light emitting diode (LED). [4] These PCE values correspond to ≈160 µW cm −2 in output power density, which is large enough to operate certain indoor electronic devices such as smoke detectors (6 µW) and occupation motion detectors (28 µW). However, these values are far below the theoretical limits of 45.7% for the FL lamp and 58.4% for the LED. [26] Thus, there remains significant room for improvement.Compared to 1 sun illumination commonly considered for outdoor PVs, the indoor environment is characterized by much lower light intensities and completely different output spectra. Therefore, realization of efficient OPVs under indoor Recently, indoor organic photovoltaics (OPVs) has attracted substantial research attention, due to the emergence of self-powered electronic devices for Internet-of-Things (IoT) applications. This progress report discusses recent developments in indoor OPVs, focusing on the strategic role of synergistic parasitic resistance in suppressing the leakage current to achieve high indoor efficiencies. Moreover, an underexplored area is presented, namely the impact of optical modulation on enhancing light absorption in indoor OPVs. First, the main advances in material design for indoor OPVs are briefly presented. This is followed by detailed discussions of the crucial strategies, including interfacial e...

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