Highly reflective rear surface passivation design for ultra-thin Cu(In,Ga) Se2 solar cells

Al2O3 rear surface passivated ultra-thin Cu(In,Ga)Se2 (CIGS) solar cellswithMo nano-particles (NPs) as local rear
contacts are developed to demonstrate their potential to improve optical confinement in ultra-thin CIGS solar
cells. The CIGS absorber layer is 380 nm thick and the Mo NPs are deposited uniformly by an up-scalable technique
and have typical diameters of 150 to 200 nm. The Al2O3 layer passivates the CIGS rear surface between
the Mo NPs, while the rear CIGS interface in contact with the Mo NP is passivated by [Ga]/([Ga] + [In]) (GGI)
grading. It is shown that photon scattering due to the Mo NP contributes to an absolute increase in short circuit
current density of 3.4 mA/cm2; as compared to equivalent CIGS solar cells with a standard back contact.