Role of selenium content in selenization of inkjet printed CIGSe2 thin film solar cell

Abstract

The presence of fine grained layer in Cu (In, Ga) Se2 (CIGSe) thin film can largely impedes the performance of solar cell; problem was well identified in earlier reports however not researched and addressed systematically. In this context, present work proposes a systematic experimental strategy to reduce this fine grained layer thickness to a great extent, evident in improvement of final cell performance. CIG precursor layer was deposited by inkjet printing technique using an aqueous based ink followed by atmospheric selenization in rapid thermal annealing (RTP) furnace. A set of selenization experiments was carried out by varying the number of selenium pellets (2, 4 and 8) in a fixed volume of closed graphite box by keeping other selenization conditions (temperature and time) constant. In all cases, single phase CIGSe films with clear bi-layered structure were formed which were further analyzed by XRD, Raman and FESEM characterization techniques. It is understood that during selenization, Se flux is highly influential in forming bilayer structure with reduction in fine grain layer by increasing number of Se pallets. Reduction in fine grained layer led to improve the photoconversion efficiency from 1.05 % to 3.43 % of the CIGSe solar cells on an active area of 4 mm x 4 mm. Moreover, the samples prepared with high selenium flux exhibited MoSe2 formation at the junction of CIGSe and Mo thin film.