High work function transparent middle electrode for organic tandem solar cells

Abstract

The use of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) in combination with ZnO as middle electrode in solution-processed organic tandem solar cells requires a pH modification of the PEDOT:PSS dispersion. We demonstrate that this neutralization leads to a reduced work function of PEDOT:PSS, which does not affect the performance of polythiophene:fullerene solar cells, but results in a lower open-circuit voltage of devices based on a polyfluorene derivative with a higher ionization potential. The introduction of a thin layer of a perfluorinated ionomer recovers the anode work function and gives an open-circuit voltage of 1.92 V for a double junction polyfluorene-based solar cell.

Impact of unbalanced charge transport on the efficiency of normal and inverted solar cells

“…5, 26 The inverted tandem is structured as follows: A The front and back active layers, however, have now different optical and electrical characteristics, as the optimized polymer band gaps for both layers in a tandem device differ from that in a single celled device. 22 An optimum performance for tandem devices is obtained for polymer band gaps of 1.9 eV and 1.5 eV for the front and back device, respectively.…”

Enhanced efficiency in double junction polymer:fullerene solar cells

“…After centrifugation, the ZnO gels were dispersed in acetone [16], followed by sonication and filtration. The acidity of PEDOT:PSS (Clevios PH500, H.C. Starck) was tuned by addition of a 1:8 dilution of 2-dimethylaminoethanol in water [17]. Nafion perfluorinated resin solution (5 wt% in a mixture of lower aliphatic alcohols and water, Aldrich) was diluted 1:20 with ethanol before spin coating at high rpm on top of pH-modified PEDOT:PSS layers in a nitrogen-flushed compartment under ambient atmosphere.…”

Hole-enhanced electron injection from ZnO in inverted polymer light-emitting diodes

“…However, through thermal annealing or under UV radiation, the absorbed oxygen on TiO 2 or ZnO surface can be released and the fabricated PLEDs can be recovered [4]. Because of its conductivity, suitable energy levels and transparency, ZnO has been widely used as electron-extracting contact in organic photovoltaics (OPVs) [5][6][7]. The ZnO we use has a work function of 4.2 eV [6], as measured with a Kelvin probe (for more details see Section 2).…”