Application Of ZnO Nanoparticles Based On Interfacial Modification As An Electron Transport Layer In Polymer Solar Cells

With the increasing photovoltaic performance of organic solar cells,there is an urgent need to address the commercialisation of organic solar cells.Despite the power conversion efficiency of currently available active layer materials exceeding 18%,defects in the transport layer remain a major obstacle to the commercialisation of organic solar cells,for example the conventional cavity transport material poly 3,4-ethylenedioxythiophene/polystyrene sulfonate(PEDOT:PSS),which directly affects the charge diffusion and stability of the active layer material due to its acidity.Also,sol-gel ZnO is not compatible with commercial roll-to-roll processes due to its high temperature crystallisation for the preparation of ZnO films.Therefore,in order to achieve the production and fabrication of high performance polymer solar cells,zinc oxide nanoparticles(ZnO NPs)with high electron mobility and transparency,which can be processed at low or room temperature,were chosen as the electron transport layer for organic solar cells in this study.The simple doping and compounding of the electron transport layer provides an effective means of preparing simple and efficient inverted organic solar cells.The research in this thesis is divided into three main parts as follows:(1)The polymer electrolyte poly(9,9-bis(3’-(N,N-dimethyl)-Nethylammonium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide(PFN-Br)was added to the ZnO NPs dispersion.The distribution of nanoparticles in the dispersion system is adjusted to obtain denser,more uniform and smoother films of ZnO NPs.The effect of ZnO NPs with different doping concentrations on the performance of photovoltaic devices has been investigated by studying the morphology and conductivity of the ZnO NPs films before and after doping.The experiments show that the use of PFN-Br doping for ZnO NPs is effective and that the carrier extraction of organic solar cells with PFN-Br doping is substantially increased.(2)To further produce highly efficient inverted organic solar cells,N-type small molecules N,N’-bis(N,N-dimethylpropane-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide(PDINO)were doped into the ZnO NPs dispersion.The introduction of PDINO not only regulates the distribution of nanoparticles in the dispersion system,but also significantly reduces the surface function of ZnO NPs,resulting in a further reduction of the voltage loss at the interface and an increase in the open-circuit voltage of the doped device from 0.82 V to 0.85 V.The device efficiency is also further improved.(3)A green natural dextran(Dex)was chosen as the functional modification layer to passivate the surface defects of sol-gel ZnO caused by high temperature annealing crystallization to prepare a ZnO/Dex composite electron transport layer.It was found that the ZnO/Dex composite layer has a lower surface function,higher charge extraction capacity and the electron mobility of single-electron devices with ZnO/Dex composite films is more than twice that of single-layer ZnO,resulting in more efficient photovoltaic devices.