Close-Spaced Sublimation Processed Environment-Friendly Planar Heterojunction Antimony Sulfide Solar Cells

The exponential growth of the Internet of Things (IoTs) electronics calls for the development of more energy-saving solutions to replace commonly used batteries. The indoor photovoltaics (IPVs), capable of harvesting energy from ambient lighting, emerge as an advanced energy-supply technology for sustainable IoTs. The binary semiconductor antimony sulfide (Sb2S3) has a suitable bandgap of ~1.75 eV, close to the optimal value for IPVs. In this work, environment-friendly planar heterojunction Sb2S3 solar cells using TiO2 buffer layers were constructed via close-spaced sublimation (CSS). Through careful characterization of morphological, structural, and optoelectronic properties, it is revealed that, compared to the conventional CdS-based Sb2S3 films, the TiO2-based Sb2S3 films exhibit more compact morphology, improved [hkl, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${l} \ne ~0$ </tex-math></inline-formula>]-orientation, and more favorable band structure. Particularly, the significantly reduced parasitic absorption of TiO2 buffer layers over the short-wavelength range contributes to the remarkable photocurrent enhancement of devices. As a result, the TiO2/Sb2S3 heterojunction device yields a power conversion efficiency (PCE) of 4.55% under one-sun (AM1.5G, 100 mW cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{2}}$ </tex-math></inline-formula>), outperforming that of the CdS/Sb2S3 device (4.11%). To the best of our knowledge, this is the highest efficiency value reported thus far for CSS-processed Sb2S3 systems. Moreover, an appreciable indoor efficiency of 12.14% is achieved for the TiO2/Sb2S3 solar cell under 1000-lx white light-emitting diode (WLED) illumination. This work manifests the great potential of CSS-processed environment-friendly planar heterojunction Sb2S3 solar cells for highly efficient and stable IPVs.