High Crystalline Additives Optimizing The Morphology Of Active Layer And Its Devices For Organic Solar Cells

Organic solar cells have drawn much attention in the last decades because of their light weight and low-temperature solution processing. The morphology of active layer have a big effect on improving the device performance, expescially for the formation of bicontinuous interpenetrating network structure with appropriate phase separation size. However, crystallization is a driving force to acquire the interpenetracting network structure and promote phase separation. This article presents a novel method which is the method of adding a high-crystalline component to increase the crystallinity of donor and optimize the morphology of active layer. The method could improve the power conversion efficiency of devices and have been proved by several systems.Firstly, poly(3-butylthiophene)(P3BT) nanowires were incorporated into P3HT:PCBM to optimize the morphology of the active layer. The P3BT-nw were found to induce the crystallization of P3 HT and facilitate the aggregation of PCBM molecules into larger clusters. The PCE of the ternary blend device could reach to the highest value of 4.2% at P3BT-nw weight percentage of 7 wt%, in comparison with the pristine P3HT:PCBM system of 3.0%. The improved performance should be associated with the enhanced hole and electron mobilities, due to the formation of interconnected channels along the crystallites of P3 HT and P3BT-nw for efficient long-range charge transport.Secondly, morphological control over the bulk heterojunction of p-DTS(FBTTh2)2:PC71BM was demonstrated by introducing a small amount of P3 BT into the active layer. The P3 BT could serve as a heterogeneous nucleating agent, inducing the crystallization of p-DTS(FBTTh2)2 to form interconnected nanofibers throughout the whole film. Moreover, the phase separation sizes increased after incorporation of P3 BT, accompanied by the enhanced surface roughness of the films. Therefore, the power conversion efficiency increased from 3.4% to 5.0% as the P3 BT content reached to 10 wt%, due to the enhanced light absorbance and the higher and more balancedelectron and hole mobility.Finally, a high crystalline small molecule which was named DPP-TP6 was synthesized, and the DPP-TP6 small molecules were incorporated into the PTB7:PC71BM solar cells to optimize the morphology of active layer. The addition of DPP-TP6 could promote the formation of bicontinuous interpenetrating network structure, thereby improving the hole mobility. Eventually, the power conversion efficiency of the device with 8 wt% DPP-TP6 increased from 6.50% to 7.85%.