Dr Homare HIROI

Dr Homare HIROI

Project Leader
Showa Shell Sekiyu K.K. & Solar Frontier K.K., Tokyo Institute of Technology, Japan

New Challenge in Se-free Cu(In,Ga)S2 Solar Cells

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.


From 2010 to 2014, he was a Research Scientist with Atsugi Research Center, Showa Shell Sekiyu K.K. and Solar Frontier K.K. in Japan. He was also a Visiting Researcher with T. J. Watson Research Center, IBM, USA, focusing mainly on research of kesterite solar cells.

 Since 2014, he has been a Project Leader of CIS R&D with the Technology Development Division, Solar Frontier K.K. His current research interests include high-performance (CIGSe-based) and low-cost (Se-free CIGS-based and CZTS-based) chalcogenide solar cells.

 Mr. Hiroi was a recipient of the PVSEC Best Paper Award (PVSEC-23, 2013).