Alexander W. Hains

High-efficiency hole extraction/electron-blocking layer to replace poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) in bulk-heterojunction polymer solar cells

An anode interfacial layer is reported for bulk-heterojunction (BHJ) polymer solar cells to replace the commonly used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). A poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB)+4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi2) blend is crosslinked, forming robust ∼10nm thick films covalently bound to indium tin oxide, which transport holes while blocking misdirected electrons. The thermal stability and photovoltaic performance metrics of TFB:TPDSi2-modified BHJ cells are significantly greater than those of cells fabricated in parallel with PEDOT:PSS or with no interfacial layer. For a poly[2-methoxy-5-(3′,7′-dimethyloctyloxyl]-1,4-phenylene vinylene: methanofullerene[6 6]-phenyl C61-butyric acid methyl ester cell, Voc=0.89V, Jsc=4.62mA∕cm2, FF=54.4%, and ηp=2.23%.

Spatially resolved photocurrent mapping of operating organic photovoltaic devices using atomic force photovoltaic microscopy

A conductive atomic force microscopy (cAFM) technique, atomic force photovoltaic microscopy (AFPM), has been developed to characterize spatially localized inhomogeneities in organic photovoltaic (OPV) devices. In AFPM, a biased cAFM probe is raster scanned over an array of illuminated solar cells, simultaneously generating topographic and photocurrent maps. As proof of principle, AFPM is used to characterize 7.5×7.5μm2 poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester OPVs, revealing substantial device to device and temporal variations in the short-circuit current. The flexibility of AFPM suggests applicability to nanoscale characterization of a wide range of optoelectronically active materials and devices.