Applications Of Gold Nanoparticles In Polymer Solar Cells

Solar cell, which can directly convert solar energy into electricity, is one of the most significant approaches to solve the increasing serious energy crisis in the world. Due to their simple fabrication procedure, physical flexibility and low cost, polymer solar cells (PSCs) have attracted great attentions. However, compared with the inorganic solar cells, the low power conversion efficiency (PCE) of PSCs is still one of the main problems for practical applications. A major factor influencing the efficiency greatly is the limited light absorption due to the thin active layer which is limited by the short exciton diffusion length and low carries mobility of polymers. Therefore, it’s an efficient approach to enhance performance of PSCs by improving the photon absorption efficiency of active layer while keeping their thickness still thin enough to maintain the effective exciton diffusion and charge transport.Metallic nanoparticles (NPs) such as Au and Ag NPs exhibit localized surface plasmon resonance (LSPR) property. The LSPR effect can create strong near-field electromagnetic fields which can improve the optical properties of the surrounding materials. These properties make metallic NPs one of the potential candidates for improving the photon absorption efficiency of PSCs. In this thesis, we reported the performance enhancement of PSCs by incorporating Au NPs or Au NPs films in the hole transport layer (PEDOT:PSS) or the active layer.In Chapter1, the working principle, device structure and recent progress of polymer solar cells are reviewed. The applications of noble metallic nanomaterials in PSCs are also summarized.In Chapter2, we reported the enhanced performance of PSCs (ITO/PEDOT:PSS/MEH-PPV:PCBM/Al, ITO:indium tin-oxide; PEDOT:PSS:poly3,4-ethylenedioxy-thiophene:polystyrenesulfonate; MEH-PPV:poly(2-mthoxy-5(2’-ethylhexyloxy)-1,4-phenylenevinylene); PCBM:[6,6]-phenyl-C61-butyric acid methyl ester) by incorporation of a Langmuir-Blodgett assembled Au NPs monolayer between the anode and the hole transport layer. Our results show that both open-circuit voltage (Voc) and short-circuit current (Jsc) of PSCs can be improved after incorporating Au NPs monolayer. We attribute the improvement of Jsc to the LSPR effect of Au NPs films, while the improvement of Voc is due to the high work function of the incorporated oxidized Au NPs monolayer.In Chapter3, we studied the performance enhancement phenomenon of PSCs (ITO/PEDOT:PSS/P3HT:PCBM/A1, P3HT:poly(3-hexylthiophene)) by incorporation of various sized Au NPs in the anode modification layer (PEDOT:PSS). We found that the light absorption of the active layer can’t be improved until the size of Au NPs is larger than the thickness of the PEDOT:PSS layer; besides, as the size of Au NPs increased, the roughness of PEDOT:PSS increased, enlarging the interface areas between PEDOT:PSS and the active layer, and resulting in the improved hole collection efficiency at the anode. However, the morphology of the active layer would change to reduce the D/A interface area, leading to reduction of exciton dissociation efficiency, while further increasing the size of Au NPs. Therefore, the trends of Jsc and PCE of PSCs resulted from the competition between the two effects.In Chapter4, we studied the performance enhancement effect of PSCs (ITO/PEDOT:PSS/P3HT:PCBM/A1) by incorporation of Au NPs in the active layer. Our work shows that the light absorption of the active layer can be improved while the exciton dissociation efficiency would be reduced, as increasing the concentration or size of Au NPs. Meanwhile, the carrier mobilities of PSCs were improved at low Au NPs concentration, but reduced while further increasing the Au NPs concentration.In Chapter5, we reported the enhanced performance of CdSe:PCPDTBT (PCPDTBT:poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b’]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]) hybrid solar cells (HSCs) by incorporation of the same sized Au NPs in the PEDOT:PSS layer or the CdSe:PCPDTBT active layer. Compared to the control device, the PCE of HSCs improved from2.95%to3.20%after incorporating Au NPs in the PEDOT:PSS layer, due to the increased hole collection efficiency; while the PCE of HSCs improved from2.91%to3.16%after incorporating Au NPs in the CdSe:PCPDTBT active layer, resulting from the enhanced light absorption intensity and the improved hole mobility of the CdSe:PCPDTBT active layer.