This paper exploits a new charge pump used in integrated solar energy harvesting systems to improve the power efficiency under ultra low supply of under 0.7V supplied by on-chip photodiodes. Compared with conventional charge pumps, improvements of 20% in terms of output voltage gain and conversion efficiency can be achieved by using two symmetrical branches and PMOSFET-only transfer transistors per stage. The proposed circuit is implemented in UMC 0.18μm standard CMOS technology.