Advancing the Understanding of Reverse Breakdown in Cu(In,Ga)Se2 Solar Cells

Reverse breakdown is investigated in multiple Cu(In,Ga)Se
₂
solar cells with varying buffer layer thicknesses. A method to extract transition voltage, which marks the change of conduction mechanism that leads to electrical breakdown, is described as an alternative to the often less-meaningful breakdown voltage. Transition voltages for samples with CdS and Zn
_x
Sn
_1-x
O
_y
buffers are extracted from breakdown measurements performed in darkness and under illumination. The electric field is calculated for ZTO-based samples measured in darkness, and its implications for the energy band structure are examined. Fowler-Nordheim tunneling and Poole-Frenkel conduction are considered as candidates for the main breakdown mechanism in darkness. A model combining the two conduction mechanisms is proposed, and fits for experimental data are presented and discussed. Involvement of defects is debated, and defect-and-breakdown-related phenomena are showcased.