Computer simulation and modeling of the graded bandgap CuInSe2 /CdS solar cell

One of the ways to improve the low open circuit voltage (V_oc ) seen in CuInSe₂(CIS)/CdS solar cells is to use graded bandgap (position-dependent composition) absorber material (CuInGaSeS [CIS^*]) in these cells. Bandgap grading introduces effective force fields in addition to the existing electrostatic field; this results in increased collection efficiencies if effective force fields are suitably oriented. This paper presents a p-i-n model for the graded bandgap CIS^*/CdS solar cell. The model provides for multiple reflections within the intrinsic region to ensure complete absorption of incident light. This optical confinement in the intrinsic region results in 25-40% increase in photons absorbed depending on the grading profile. Numerical simulations carried out to obtain the I-V curve show that suitable bandgap grading (linear and notch type) of the absorber material in the intrinsic region (p-i-n model) of CIS^* solar cells can cause substantial improvement in the V_oc, fill factor and efficiency