KF Postdeposition Treatment in N2 of Single-Stage Thin Cu(In,Ga)Se2 Absorber Layers

Thin (<500 nm) single-stage co-evaporated Cu(In,Ga)Se2 absorber layers are treated with a KF postanneal in N2 atmosphere. The conditions of the postanneal initial acceptor concentration and the temperature are varied. Solar cells are characterized with current–voltage and capacitance–voltage measurements. Efficiencies up to 12% with an open-circuit voltage (Voc) of > 640 mV were achieved after the KF treatment. From SCAPS simulations and temperature dependent current voltage measurements, it is concluded that the Voc of these cells are limited by back contact surface recombination and, thus, further improvements require passivation of the back contact.