The role of amorphous silicon and tunneling in heterojunction with intrinsic thin layer (HIT) solar cells

This work analyzes heterojunction with intrinsic thin layer (HIT) solar cells using numerical simulations. The differences between the device physics of cells with $p$ - and $n$ -type crystalline silicon $\left(c\text{-Si}\right)$ wafers are substantial. HIT solar cells with $n$ -type wafers essentially form a $n/p/n$ structure, where tunneling across the junction heterointerfaces is a critical transport mechanism required to attain performance exceeding 20%. For HIT cells with $p$ -type wafers, only tunneling at the back-contact barrier may be important. For $p$ -wafer cells, the hydrogenated amorphous silicon $\left(a\text{-Si}:\text{H}\right)$ between the indium tin oxide (ITO) and crystalline silicon may act as a passivating buffer layer but, otherwise, does not significantly contribute to device performance. For $n$ -wafer cells, the carrier concentration and band alignment of this $a\text{-Si}:\text{H}$ layer are critical to device performance.