Lift-off process and rear-side characterization of CuGaSe2 chalcopyrite thin films and solar cells

Abstract

An alternative approach to the so-called “lift-off” technology is presented, in which a CuGaSe2 solar cell absorber film is detached from a Mo-coated glass substrate. The proposed lift-off takes advantage of an interfacial MoSe2 layer, acting as a sacrificial layer, which forms at the rear contact during the growth of the CuGaSe2 film. No additional processing step is thus required to proceed with the lift-off. The lift-off was carried out in ultrahigh vacuum for quality assessment, and the rear CuGaSe2 and top MoSe2 surfaces were characterized by means of surface-sensitive techniques, namely, Kelvin probe force microscopy and photoelectron spectroscopy. The cleanness of the CuGaSe2 rear surface was confirmed by the absence of Mo remnants, thus demonstrating the suitability of the proposed method for further processing of the absorber film onto alternative substrates. In addition, a quantitative analysis of surface photovoltage, doping concentration, and interface charge at grain boundaries on the absorber’s rear surface is presented, exploiting the convenience of the procedure for characterization purposes. Preliminary results regarding the device performance and identification of limiting factors are reported.