Achieving High Performance Polymer Solar Cells Via Incorporating Electrodes Buffer Layers

With the growing consumption of fossil energy， the energy issue is becoming amajor strategic issue of great concern to all countries in the world. As a promissingclean energy， solar energy is considered as an alternative energy sources. This hasbeen partly achieved by commercialized inorganic semiconductor (monocrystallinesilicon， polycrystalline silicon and amorphous silicon) solar cells. However， dueto the requirments of high quality materials and the complex fabrication processes，the manufacturing of inorganic solar cells needs to consume large amounts ofenergy， resulting in a relatively high cost.In the contrast， polymer solar cells (PSCs) are considerd to be compatible withindustrial large area manufacturing system due to its advantage of using wetdeposition method to make devices. Compared to the inorganic silicon solar cellmaterial， polymer materials is much more extensive. In additional， since polymersolar cells can be fabricated by room temperature solution processing (such as spincoating， spray deposition， roller printing， ink-jet printing，etc.)， it bears thepotential of making large area flexible polymer solar cells. Though deleoped fast inthe past decades， PSCs still suffer from low power convertion effectioncy.In order to improve the device performance of polymer solar cells， weinvestigated the influence of interlayers. By incorporation of a kind of water/alcohol-soluble conjugated polymer (PFN) as an cathode interlayer， we achievedsimultaneouse enhancements of open-circuit voltage (Voc)， short circuit current(Jsc) and fill factor (FF) of the devices， which made the energy conversion efficiency(PCE) of the device a substantial increase.And a PCE over8%for asingle-junction PSCs was achieved for the fisrt time in scientific literatures. Tovisualize the surface potential change around the interlayer area derectly， theSurface Kelvin Probe Microscopy (SKPM) was carried out.And the existent of aninterfacial dipole was found intuitively for the first time. To find out the influence ofthe diploe layer on the charge transport properties of PSCs， we analyzed theelectrical properties of the interface dipole layer and found out that the superpositionof the interfacial dipole moment and the built-in potential originated from theasymmetric contacts between the electrodes of the devices was responsible for theenhanced Voc. We also confirmed that by incopration this kind of interlayers， thecharge transport property (chager apparent mobility) was inproved and bimolecularrecombination was suppressed in the PSCs. And what is more important， byinvestigating the effect of PFN cathode interlayer on various donor materials PSCssystems， we found that this kind of interlayers worked universally in PSCs， whichhave caused world wide follow-up studies.Through device structural innovation， we made inverted PSCs devices byincorperation of PFN as ITO modifier for the first time. By simultaneouslyoptimizing electrical contact between the substrates and the active layers and opticalproperty by interference effect of the devices， the Jsc of the devices was enhanced，resulting in a PCE over9%for a single-junction PSCs.