Carbon layer reduction via a hybrid ink of binary nanoparticles in non-vacuum-processed CuInSe2 thin films

To reduce the thick carbon layer between the Mo back contact and the CuInSe2 (CIS) absorber in non-vacuum-processed CIS solar cells, a hybrid ink was used to form a CuInSe2 (CIS) thin film. The hybrid ink consists of binary nanoparticles (CuS and In–Se) and a precursor solution. Binary nanoparticles were synthesized by a low-temperature colloidal process and acted as stress-relief and crack-deflection centers in the hybrid ink. A precursor solution was prepared with a chelating agent that acted to effectively bind the nanoparticles without other binders. In particular, the use of nanoparticles made it possible to reduce the carbon layer due to the easy removal of organics in the precursor solution through the pores between the nanoparticles. The thickness of the formed CIS layer was 1.22 μm, and the thickness ratio of the CIS layer/carbon layer (CIS/carbon) was almost 1. The fabricated device with this thin film showed a reproducible conversion efficiency of 5.87% and a band gap of 1.11 eV.