World record efficiency of 22.3% Cu(In, Ga)(Se, S) ₂ (CIGS) thin film solar cell has been achieved in Solar Frontier K.K. and certified independently by Fraunhofer Institute für Solare Energiesysteme (ISE). The device parameters are as follows, J _SC : 39.4 mA cm ^-2 , V _OC : 721.9 mV and FF: 0.782. Compared to our previous champion with 20.9% efficiency, a major improvement in V _OC (+36.1 mV) was observed due to KF post deposition treatment that improve the absorber layer and the use of CdS buffer. As we thrive to achieve the utmost ecological advantages, Cd-free buffer was also developed by replacing the ZnO/CdS buffer with optimized (Zn, Mg)O/Zn(O, S, OH) buffer layers. As a result, an in-house conversion efficiency of 22.8% was achieved. This demonstrated that Cd-free CIGS solar cell still possesses huge potential and we will continue to explore new pathways to achieve higher efficiency CIGS solar cells.