All-small-molecule Organic Solar Cells Based On Porphyrin Donors

With the energy and environmental problems becoming more and more serious,organic solar cells（OSCs）have become an important research topic that has attracted widespread attention due to their light weight,flexibility,solution processing,and potential roll-to-roll large-area processing.At present,the highest power conversion efficiency of single-junction organic solar cells based on polymer systems has reached 18%.However,polymer materials often have the problems of batch difference and poor repeatability,so people have gradually started to study organic photovoltaic materials based on all-small-molecule systems.And the power conversion efficiency of single-junction organic solar cells based on all-small-molecule systems also exceeds 15%,which has extremely broad application prospects.For all-small-molecule systems,in order to obtain a high power conversion efficiency system,in addition to designing a narrow band gap acceptor material to obtain more photoexcitons,increasing and balancing the charge transfer rate of the device and improving the phase separation size of the active layer,then reducing the occurrence of charge recombination can also greatly improve the efficiency of exciton dissociation and collection,and then improve the power conversion efficiency of the device.In Chapter 2,we blended the alkyl side chain modified small molecule porphyrin donor C₂₀Zn P-2DPP and the thiophene side chain modified small molecule porphyrin donor TEHZn P-2DPP with the non-fullerene acceptor IDIC and the fullerene acceptor PC₆₁BM to make the organic solar cell devices,and the reasons how the small molecules donors affected the photovoltaic performance of the devices under different systems were investigated.For non-fullerene IDIC systems,the FF of the C₂₀Zn P-2DPP:IDIC device is higher than that of TEHZn P-2DPP:IDIC.This is because C₂₀Zn P-2DPP has a stronger intermolecular interaction,which improves the electron and hole mobility of the device,gains higher exciton dissociation and collection probability.As for the fullerene PC₆₁BM system,TEHZn P-2DPP molecules have increased steric hindrance and reduced intermolecular interactions.Therefore,the TEHZn P-2DPP:PC₆₁BM system obtains a more appropriate phase separation size and a more balanced charge transfer rate,gains higher exciton dissociation and collection probability.In Chapter 3,we doped PC₆₁BM into an all small molecule system based on porphyrin donors.Compared with the binary devices,the ternary devices show significantly increased short-circuit current J_SC and fill factor FF.The experimental results show that the addition of PC₆₁BM not only enhances the absorption of the mixed film in the ultraviolet region to a certain extent,but also improves the electron mobility of the device to more balance the charge transport in the device,and improves the phase separation morphology to reduce the charge recombination.Therefore,the power conversion efficiency of the ternary device has been greatly improved.These results provide a reference for the design and synthesis of new small molecule donor materials,indicating that the ternary strategy is still very effective to improve the efficiency of organic photovoltaic devices.