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 cells with Mo 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 380nm thick and the Mo NPs are deposited uniformly by an up-scalable technique and have typical diameters of 150 to 200nm. 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 3.4mA/cm2; as compared to equivalent CIGS solar cells with a standard back contact. •Proof-of-principle ultra-thin CIGS solar cells have been fabricated.•The cells have Mo nano-particles (NPs) as local rear contacts.•An Al2O3 film passivates the CIGS rear surface between these nano-particles.•[Ga]/([Ga]+[In]) grading is used to reduce Mo-NP/CIGS interface recombination.