Solar Frontier K.K. has been working on the research of several chalcogenide solar cells, Cu(In,Ga)(Se,S)2 (CIGSeS), Se-free Cu(In,Ga)S2 (CIGS), Cu2ZnSn(Se,S)4 and Se-free Cu2ZnSnS4. Recently, 22.3% conversion efficiency (Eff) on CIGSeS and 15.5% Eff on Se-free CIGS thin-film solar cells were achieved (both were confirmed by Fraunhofer ISE) as shown in Fig. 1 [1,2].
In this paper, we will especially focus on the Se-free CIGS solar cell and discuss about a new challenge for the Eff improvement. We have boosted the Eff of Se-free CIGS owing to open-circuit voltage and current density improvements by Ga-profile control and Cd-free buffer application. However, the fill-factor was still low, and it is assumed that the rough absorber made shunt passes. Thus, we tried to obtain the flat absorber to prevent the shunt passes. Finally, the flat absorber was obtained by a new method as shown in Fig. 2. The detail of the electrical parameters will be presented at the conference.
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