A cathode buffer layer made of CdSe quantum dot (QD) is introduced in inverted poly(3-hexylthiophene) (P3HT): Indene-C 60 Bis-Adduct (ICBA) inverted bulk heterojunction (IBHJ) solar cell. The open-circuit voltage and fill factor increase respectively to 0.88V and 68.71%, due to the enhanced electron extraction by inserting a CdSe QD layer on Cs 2 CO 3 /ITO cathode. Thus, the power conversion efficiency increases from 4.6% to 5.2% and the environmental stability is also much improved. By analyzing transmission electron microscope and energy dispersive X-ray spectroscopy, it is found that CdSe QD layer retards Cs diffusion into active layer, leading to improve the lifetime. The ideal temperature dependence of V OC under various illuminations has been achieved with the maximum V OC of 1.205V.