Flexible multi-layered coloring transparent electrode composed of AZO–based materials

Color implementation in flexible photovoltaics (PVs) is aesthetically important in modern vehicles and buildings. To implement color in flexible PVs using conventional distributed Bragg reflector (DBR) methods, it is necessary to reduce its brittleness and minimize the light loss due to refractive index differences (Δn). Here, color-implemented transparent front electrodes for flexible and transparent solar cells (FTSCs) have been proposed using an aluminum-doped zinc oxide (AZO)–based multilayer with periodic hydrogenation (AZO:H). The hydrogenation of AZO causes passivation in vacancies of oxygen and zinc and strengthening of the O–H bonds, resulting in improved of electrical and optical properties and a very low Δn of ∼5%. Using the AZO:H DBR–diffuser electrodes, we demonstrate three primary colors and colored FTSCs made of silicon thin film. The FTSCs show little change in power conversion efficiencies for the different colors owing to low return loss by the very low Δn. They are lightweight for their high specific power and exhibit excellent flexibility that enables them to endure the bending stress of 600 cycles at a 6 mm bending radius. The developed device can be used for vehicle and building-integrated PV applications, and the methodology can be used for other thin-film solar cells that require color and flexibility.