Optimized n-type amorphous silicon window layers via hydrogen dilution for silicon heterojunction solar cells by catalytic chemical vapor deposition

Abstract

A comprehensive study of the microstructures and properties of n-type hydrogenated amorphous silicon (n-a-Si:H) films, deposited by catalytic chemical vapor deposition, for the window layers of silicon heterojunction (SHJ) solar cells is presented. With increasing hydrogen-to-silane dilution ratio (RH), the deposited films first become dense, after which they loosen. With further increases in RH, the films tend to crystallize with native post-oxidization. The doping efficiencies of phosphorus in the various n-a-Si:H films are similar, but the upper surface doping levels of the films are affected by RH. The post-oxidized n-a-Si:H film is more transparent at short wavelengths than a dense film deposited at low RH, exhibiting an external quantum efficiency gain of 20% at 300 nm. Finally, a higher efficiency and short-circuit current density (Jsc) are obtained with the post-oxidized n-type a-Si:H window layer; a Jsc gain of 0.25 mA/cm2 and an efficiency increase of 0.36% were achieved for the optimized SHJ solar cell. At the device level, a dense intrinsic a-Si-H passivated layer is beneficial for suppressing fill-factor (FF) deterioration. The natively post-oxidized n-a-Si:H window layer is a potential choice for improving Jsc by apparently enhancing light absorption in crystalline silicon at short wavelengths.