The Photovoltaic Performance Of Solar Cells Based On Organic Small Molecules And Perovskites

Accompanied by the energy crisis and the environmental pollution, more andmore people pay their attention to the field of organic solar cells, which can befabricated with low-cost and large-scale production. As is known to all, organic smallmolecular and perovskite solar cells recently play a key role in the photovoltaic field.Among them, the photoelectric conversion efficiency (PCE) of organic smallmolecular solar cells has reached about9%. Meanwhile, PCE over20%has beenreported for perovskite solar cells. With the rapid advance of the PCEs, the problemsexisting are also obvious.Firstly, the ideal active layer must efficiently absorb the light, simultaneously,minimizing the probability for excitons recombination, thereby contributing to thegeneration, dissociation and transport of more charge. To achieve high fill factor (FF)and PCE, several effective methods have been developed to optimize the phaseseparation, including thermal annealing, solvent mixtures, and additives. However,the complicated mechanism of these methods in tuning the morphology limits theiruniversality. Furthermore, all the methods mentioned above to tune the morphologygreatly increases the cost and period of the device fabrication.Secondly, the thickness of active layer is limited by the electronic transport layercomposed by ZnO nanoparticles in perovskite solar cells. Therefore, the generatedexciton in the active layer cannot separate and transport well. In the device with thestructure of ITO/ZnO/Perovskite/P3HT/Ag, the interface between the active layer andthe hole transport layer cannot contact well, leading to the device with lower fillfactor.To solve the problems mentioned above, two solutions are designed and putforward in this thesis as follows: 1. In this paper, a series of new D-A small molecules which have the differentalkyl chain length are designed and synthesized. Among these small molecules, alkylchains with different length are introduced for investigating their effect on molecularthermal, optical, electrochemical properties as well as photovoltaic performance. Byadjusting the length of alkyl chain, optical density can be significantly increased. Inthis way, the active layer can absorb more photons and its morphology can be wellcontrolled. Sequentially, the FF of the device has been improved remarkably and thePCE was significantly enhanced from1.25%to3.18%.2. ZnO nanoparticles with mall grain size are prepared utilizing sol-gel methodand is used as the electron transport layer in perovskite solar cells. When heated, themesoporous structure can be achieved by the aggregation of the nanoparticles. Thisstructure can contribute to increase the short-circuit current (Jsc) of the devices. At thesame time, we adopted the solution method to dope MoO3into P3HT as the holetransport layer, resulting in improved interface morphology between active layer andhole transport layer. As a consequence, the device exhibited a better performanceattributing to the high fill factor.