Diffusion-free back-contact solar cells on S-passivated p-type Si(100) substrates

In back-contact solar cells, the emitter is conventionally formed by diffusion of a n-type dopant into a p-type substrate. We demonstrate a back-contact solar cell without diffusion. The p-n junction in our cell is formed by the record-high Schottky barrier of 1.1 eV between low work-function aluminum and sulfur-passivated p-type Si(100) surface. The high Schottky barrier induces degenerate inversion on the surface of p-type Si, leading to the formation of a p-n junction without diffusion. The sulfur passivation process is performed by immersing the Si substrate in an aqueous solution containing ammonium sulfide. Although the conversion efficiency is low in this cell (∼1%), it can be significantly increased by employing a chemical vapor deposition process for passivation and by optimizing several material/device parameters.