Indoor photovoltaic energy harvesting based on semiconducting π-conjugated polymers and oligomeric materials toward future IoT applications

With the advancement of artificial intelligence computing systems that can collect, analyze, and utilize metadata from our activities and surrounding environments, establishing self-powered electronic systems/networks supported by energy harvesters is strongly desired. With the lowering of power consumption in contemporary IoT electronics such as wireless sensors, indoor organic photovoltaic devices (iOPVs), which can be driven under ambient indoor light, have recently attracted significant interest as self-sustainable eco-friendly power sources. iOPVs based on organic semiconductors have unique advantages, such as light weight, flexibility, solution processability, and feasibility of low-temperature mass production. Additionally, the spectral tunability and high optical absorptivity of organic semiconductors make iOPVs more effective as energy harvesters in indoor lighting environments. With recent intensive research effort, iOPVs have realized the delivery of high power conversion efficiencies exceeding 25% with output power densities of several tens to a hundred μW cm⁻², which are sufficient to drive various low-power electronics compatible with the IoT. This review article focuses on recent progress in iOPVs based on π-conjugated polymers and oligomeric materials and outlines their fundamental principles and characterization techniques.