Anode Interfacial Tuning via Electron-Blocking/Hole-Transport Layers and Indium Tin Oxide Surface Treatment in Bulk-Heterojunction Organic Photovoltaic Cells

摘要

The effects of anode/active layer interface modification in bulk-heterojunction organic photovoltaic (OPV) cells is investigated using poly(3,4-ethylenedi-oxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and/or a hole-transporting/electron-blocking blend of 4,4'-bis[(p-trichlorosilylpropylphenyl)-phenylamino]biphenyl (TPDSi_2) and poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) as interfacial layers (IFLs). Current-voltage data in the dark and AM1.5G light show that the TPDSi_2:TFB IFL yields MDMO-PPV:PCBM OPVs with substantially increased open-circuit voltage (V_(oc)), power conversion efficiency, and thermal stability versus devices having no IFL or PEDOTrPSS. Using PEDOTrPSS and TPDSi_2:TFB together in the same cell greatly reduces dark current and produces the highest V_(oc) (0.9T V) by combining the electron-blocking effects of both layers. ITO anode pre-treatment was investigated by X-ray photoelectron spectroscopy to understand why oxygen plasma, UV ozone, and solvent cleaning markedly affect cell response in combination with each IFL. O_2 plasma and UV ozone treatment most effectively clean the ITO surface and are found most effective in preparing the surface for PEDOT:PSS deposition; UV ozone produces optimum solar cells with the TPDSi_2:TFB IFL. Solvent cleaning leaves significant residual carbon contamination on the ITO and is best followed by O_2 plasma or UV ozone treatment.