The Design And Fabrication Process Of Seed-Layer-Induced Nano-phase Structure To Organic Photovoltaic Device

With world economic development and continuous depletion of traditional non-renewable energy, newenergy technology has become an important force to solve the energy problems. Solar power for itssustainable, environmental and other advantages becomes an important way to solve the energy problem.At present, traditional crystalline silicon cells because of its complex process, high energy consumption andelectricity generation cost seriously hampered the development of solar energy.Organic photovoltaic has considerable technological potentials as an alternative, renewable source ofenergy, and offers the combined attraction of light-weight, flexibility and low cost to manufacture withlarge-area and simple fabricating processes. However, the relatively low power conversion efficiency （PCE）is considered to be the main obstacle for commercialization. With the purpose of improving the PCE oforganic photovoltaic device, it was focused on the optimization of performance by optimizing fabricationprocess and designing novel structure, solution annealing, thermal treatment, and on the concentration ofP3HT: PCBM blend by additive, as following the four aspects:（1） The bulk heterojunction structure devices are fabricated. With optimizing the speed of spin coating,the concentration of the active layer for spin-coating, and the concentration of1,8-octanedithiol in P3HT:PCBM blend, a better surface morphology was obtained, and a better two-phase separation in the activelayer. Ultimately, the device efficiency PCE is2.68%.（2） The solvent effect on device performance is observed when spin coating a active layer respectivelywith chlorobenzene, o-dichlorobenzene, and1,2,4-trichlorobenzene. The SEM cross-section images of theconventional device show the sandwich structure of the device. With the comparison of AFM topographyand phase images of the active layer, the important reason of low short-circuit current is that there is not aneffective interpenetrating network heterojunction in active layer. The phase separation in active layer ismore controllable when using o-dichlorobenzene solvent than the volatile chlorobenzene solvent.1,2,4-trichlorobenzene because of its high boiling point, is not the right solvent for spin-coating activelayer which will be too thin to harvest enough the solar light. By o-dichlorobenzene, the higherperformance of the devices is3.4%.（3）The new P3HT seed-layer-induced nano-phase structure is designed and fabricated by theUP-SIDE-DONE （USD） method and its device structure is ITO/PEDOT:PSS/P3HT/P3HT:PCBM/LiF/Al. The introduction of a very thin layer of P3HT film between the PEDOT: PSS and active layer could induceand regulate the crystalline morphology of the active layer and the carrier transport channel. It is optimizedby controlling the concentration of spin-coating solution, induced layer thickness, annealing time andconditions to get a better fabrication process. Through the analysis of J-V curves of various devices, andexternal quantum efficiency, UV-visible absorption spectroscopy it is found that this kind of structureimproves the fill factor （FF） and the short-circuit current density (J_sc) of the device. Also it improves thepower conversion efficiency of the devices. By the pre-spin-coated P3HT seed layer with the concentrationof0.4%, the performance of the novel devices obtain the optimal short circuit current density J_sc with12.59mA/cm², and the highest power conversion efficiency PCE of4.29%.（4）Two types of inverted devices were fabricated which areITO/ZnO-NWs/P3HT: PCBM/HMDS/PEDOT: PSS/AgFTO/TiO₂/P3HT: PCBM/HMDS/PEDOT: PSS/Ag.By P3HT seed-layer-introduced nano-phase structure method, the inverted devices were fabricated forchecking if this kind active layer could match the inverted structure. It was found that the inverted structureinduced by P3HT seeds layer has a short circuit current density J_sc with11.51mA/cm²and the final powerconversion efficiency PCE is3.87%.