Quantifying native and cut edge recombination of silicon solar cells

Abstract

To measure edge recombination of silicon solar cells, a refined perimeter to area methodology is presented and applied to a set of finished silicon heterojunction (SHJ) solar cells from an industrial batch. Different sample sizes are cut from these by thermal laser separation (TLS), giving samples with thermally cleaved, laser scribed and natively processed edges that are investigated. Surface recombination velocities are determined for all three edge types at injection levels of $\Delta n=\left(10^{14}\mathrm{to}10^{15}\right){\mathrm{cm}}^{-3}$, with values at $\Delta n=\text{10}{}^{\mathrm{15}}\text{cm}{}^{\mathrm{-3}}$ being $S_{\text{native}}=\text{250}\text{cm/s}$, $S_{\text{TLS}}=\text{750}\text{cm/s}$ and $S_{\text{scribe}}=\text{11 000}\text{cm/s}$. The injection dependence is dominated by recombination of ideality 2, with line-specific saturation current densities of $j_{\mathrm{02,native}}^{\lambda }=\text{2.41}\text{nA/cm}$, $j_{\mathrm{02,TLS}}^{\lambda }=\text{7.77}\text{nA/cm}$ and $j_{\mathrm{02,scribe}}^{\lambda }=\text{115}\text{nA/cm}$. The corresponding efficiency losses are approximated by numerical simulations with $\Delta {\eta }_{\text{native}}=\text{-0.1}\text{\%}$ for the full cell as well as $\Delta {\eta }_{\text{TLS,half}}=\text{-0.3}\text{\%}$ and $\Delta {\eta }_{\text{TLS,shingle}}=\text{-1.1}\text{\%}$ for the TLS-cut half- and shingle cells. Overall, the method can be employed to quantify injection-level-dependent edge recombination on finished solar cells for accurate edge loss analysis and process optimization.