Assessing the impact of back-contact recombination on CIGS solar cells with improved crystal quality

The impact of back-contact recombination on Cu(In,Ga)Se
₂
(CIGS) cells is discussed based on device simulations in which the typical Ga/III grading is considered. When the diffusion length (L
_n
) is large relative to the absorber thickness, there is room to improve open circuit voltage (V
_OC
) by preventing back-contact recombination. Whereas with small L
_n
, the impact of back-contact recombination is negligible. Efficiency gains can be realized by employing contact passivation techniques and/or larger conduction band grading which keep electrons away from the back contact.