Fabrication of the (Y2O3:Yb-Er)/Bi2S3 composite film for near-infrared photoresponse

Harvest of near infrared (NIR) radiation in photovoltaic devices is highly desirable as it is recognized as a potential pathway to break the Shockley-Queisser limit of solar conversion efficiency. Here, (Y2O3:Yb-Er)/Bi2S3 composite films with photoactive current generation under NIR light excitation were fabricated by electro-deposition and a simple successive ionic layer adsorption and reaction (SILAR) method. The composite films consist of homogeneous crystalline particles of Y2O3 with a lamellar morphology covered by Bi2S3 nanoparticles. Upon excitation by a 980 nm laser, the Y2O3:Yb-Er layer in the composite film converts NIR photons into visible emissions through upconversion, which is absorbed by the covered Bi2S3 nanoparticles and leads to the generation of photoelectrons. With the use of a standard electrochemical cell where the composite film serves as the photoanode, we demonstrate robust photocurrent generation in aqueous solution. This study suggests a promising strategy for the harvesting of NIR radiation in solar cells, photocatalysts, and infrared photo-detectors.