Parametric Analysis of Capacitance-Voltage Data for In-Situ Heat and Light Soaking Behavior of CIGS Solar Cells

Parametric studies of Cu(In,Ga)Se2 defect properties are examined using SCAPS-1D device model for the purpose of understanding heat and light soaking behavior. The variables and interdependencies modeled in this study include: (1) two different buffer layers: CdS vs. Zn(O,S); (2) conduction band offset between buffer and absorber; (3) buffer shallow donor density (0.05 eV below conduction band); (4) CIGS shallow acceptor density (0.05 eV above valence band); (5) CIGS deep acceptor density (0.55 eV above valence band); (6) CIGS shallow donor density ( ); (7) ionized acceptor concentration in the ordered vacancy compound near CIGS/buffer interface ( ); and (8) back contact work-function. The device metrics simulated include open-circuit voltage (VOC), apparent hole density of CIGS and space charge width at reverse bias, 0V and forward bias. While an increase in VOC is seen by increasing the shallow donor and acceptor densities, or decreasing the buffer concentration, the behavior of the forward bias space charge width W(V>0) behaves differently between the two buffer types based on the conduction band offset. Inflection in the apparent doping density (in reverse bias) is also observed by an increase in the bulk deep acceptor density and shallow donor density near the back contact. An increase in the space charge width is also observed by formation of a Schottky barrier at the back contact.