Research Of Morphology Formation And Perfprmance Of Organic Photovoltaics Based On N-type Polymer

The orgnic solar cell(OPV) is an emerging photovoltaics technology with bright properties such as low manufacturing cost, light specificgravity and good mechanical flexibility. But the organic solar cell still hasn’t meet the commercial standards caused by limited light absorption and low carrier mobility of orgnic semiconductor. In this work, for the first time, we demonstrate a generally applicable approach to enhance power conversion efficiency(PCE) by blending PTB7:PC71BM with poly(9,9-dioctylfluorene-co-benzothiadiazole)(F8BT). Then, we optimize of device performance through reasonably regulating the morphology of the active layer. The paper includes three parts:Firstly, the effect of F8 BT doped concentration on performance of PTB7:PC71BM:F8BT ternary OPVs was investigated. Compared with the control device, a PTB7:PC71BM:F8BT based ternary blend solar cell with ratio of 1:1.4:0.1 demonstrated the highest PCE at 6.43%, mainly due to improved light harvesting and energy level cascading.Secondly, the effect of four kinds of solvent, including chlorobenzene(CB), 1, 4-dichlorobenze(DCB), p-xylene(XY), and mixtures of CB and 1, 8-diiodooctane(DIO)(97 : 3 v/v%), on the morphology formation of PTB7:PC71BM:F8BT blends was investigated. XY-based device has a poor performance due to the relatively lower solubility of XY for PC71 BM. The films have obviously PC71 BM clusters leading serious excitons recombination before the excitons reached D-A interfaces. CB-based films have almost no PC71 BM clusters, with performance of 3.67%. In order to optimize the CB-based film morphology, we added DIO to CB and finally the device performance were improved from 3.67% to 6.51%. The raised performance was primarily attributed to the the fully self-assembly of the ternary blends, which is beneficial to form film with continuously nanoscale phase domain.Finally, we demonstrate, for the first time, the effect of thermal annealing on the performance of PTB7:PC71BM:F8BT ternary OPVs. A maximum PCE up to 3.25 % was obtained by thermal annealing at 120℃, leading to 60 % increase of PCE compared with the as-spun ternary OPVs. The improvement of PCE was mainly attributed to the rearrange of phase separation and more ordered film. We also demonstrate the influence of solvent vapor annealing on the morphology formation and performance of P3HT:PC71BM:F8BT ternary OPVs. The results indicated that the parameters of solvent including solubility parameter, viscosity and polarity were playing an important roles in controlling the morphology of active layers. Methanol with high solubility parameter could lead to 85% enhancement in the power conversion efficiency.