In this study, the influence of small-molecule organic hole injection materials on the performance of organic solar cells (OSCs) as the hole transport layer (HTL) with an architecture of ITO/ZnO/P3HT:PC71BM/HTL/Ag has been investigated. A significant enhancement on the performance of OSCs from 1.06% to 2.63% is obtained by using N, N′-bis(1-naphthalenyl)-N, N′-bis-phenyl-(1, 1′-biphenyl)-4, 4′-diamine (NPB) HTL. Through the resistance simulation and space-charge limited current analysis, we found that NPB HTL cannot merely improve the hole mobility of the device but also form the Ohmic contact between the active layer and anode. Besides, when we apply mix HTL by depositing the NPB on the surface of molybdenum oxide, the power conversion efficiency of OSC are able to be further improved to 2.96%.
We fabricated the inverted polymer solar cells (PSCs) with a structure of ITO/ZnO/PTB7:PC<sub>71</sub>BM/MoO<sub>3</sub>/Ag, and investigate the influence of spin coating on the device performance in this article. Through modifying the spin coating parameters, the high PSC performance could be obtained with V<sub>OC</sub>=0.769 (V), J<sub>SC</sub>=11.6 (mA/cm<sup>2</sup>), FF=58.8 % and PCE=5.26 %, respectively. The improvement of device performance was attributed to the enhanced absorption of active layer in the wavelength from 550 nm to 700 nm and the increased phase separation of PTB7:PC<sub>71</sub>BM.