One dimension solar cells simulator package (SCAPS) is used to study the possibility of carrying out thin CIGS solar cells with high and stable efficiency. In the first step, we modified the conventional ZnO:B/i-ZnO/CdS/SDL/CIGS/Mo structure by substituting the SDL layer with the P + layer, having a wide bandgap from 1 to l.12 eV. Then, we simulated the J-V characteristics of this new structure and showed how the electrical parameters are affected. Conversion efficiency of 18.46% is founded by using 1.1 μm of P + layer thickness. Secondly, we analyze the effect of increase thickness and doping density of CIGS, CdS and P +  layers on the electric parameters of this new structure. We show that only the short-circuit current density (JSC) and efficiency are improved, reaching respectively 34.68 mA/cm² and 18.85%, with increasing of the acceptors density. Finally, we introduced 10 nm of various electron reflectors at the CIGS/Mo interface in the new structure to reduce the recombination of minority carriers at the back contact. High conversion efficiency of 23.34% and better stability are obtained when wide band-gap BSF is used.