The unique electro‐optical features of organic photovoltaics (OPVs) have led to their use in applications that focus on indoor energy harvesters. Various adoptable photoactive materials with distinct spectral absorption windows offer enormous potential for their use under various indoor light sources. An in‐depth study on the performance optimization of indoor OPVs is conducted using various photoactive materials with different spectral absorption ranges. Among the materials, the fluorinated phenylene‐alkoxybenzothiadiazole‐based wide bandgap polymer—poly[(5,6‐bis(2‐hexyldecyloxy)benzo[c][1,2,5]thiadiazole‐4,7‐diyl)‐alt‐(5,50‐(2,5‐difluoro‐1,4‐phenylene)bis(thiophen‐2‐yl))] (PDTBTBz‐2Fanti)‐contained photoactive layer—exhibits a superior spectrum matching with indoor lights, particularly a light‐emitting diode (LED), which results in an excellent power absorption ratio. These optical properties contribute to the state‐of‐the‐art performance of the PDTBTBz‐2Fanti:[6,6]‐phenyl‐C71 butyric acid methyl ester (PC71BM)‐based OPV with an unprecedented high power‐conversion efficiency (PCE) of 23.1% under a 1000 lx LED. Finally, its indoor photovoltaic performance is observed to be better than that of an interdigitated‐back‐contact‐based silicon photovoltaic (PCE of 16.3%).

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...

The 2D transition metal carbides/nitrides (2D MXenes) are a versatile class of 2D materials for photovoltaic (PV) systems. The numerous advantages of MXenes, including their excellent metallic conductivity, high optical transmittance, solution processability, tunable work-function, and hydrophilicity, make them suitable for deployment in PV technology. This comprehensive review focuses on the synthesis methodologies and properties of MXenes and MXene-based materials for PV systems. Titanium carbide MXene (Ti 3 C 2 T x ), a well-known member of the MXene family, has been studied in many PV applications. Herein, the effectiveness of Ti 3 C 2 T x as an additive in different types of PV cells, and the synergetic impact of Ti 3 C 2 T x as an interfacial material on the photovoltaic performance of PV cells, are systematically examined. Subsequently, the utilization of Ti 3 C 2 T x as a transparent conductive electrode, and its influence on the stability of the PV cells, are discussed. This review also considers problems that emerged from previous studies, and provides guidelines for the further exploration of Ti 3 C 2 T x and other members of the 2D MXene family in PV technology. This timely study is expected to provide comprehensive understanding of the current status of MXenes, and to set the direction for the future development in 2D material design and processing for PVs.

OPVs with undoped ZnO electrodes showed excellent indoor performance with an efficiency of 9.5 ± 0.3% under an LED.

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