Organic-silicon Solar Cells Exceeding 20% Efficiency

Abstract

Aftera briefreview of therecent evolvement oforganic-silicon heterojunction solar cells,we present here our latest measurements of the saturation current densities (J0) and contact resistances (RC) of crystalline silicon (c-Si)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) junctions. We determine the J0values by means of contactless carrier lifetime measurements and theRCvalues by comparing sheet resistance measurements with numerical device simulations of the corresponding test structure. Application of an adopted PEDOT:PSS blend and an optimized silicon surface treatmentresults in a minimalJ0value of46 fA/cm2, limiting the solar cell open-circuit voltage to Voc-limit=708 mV, and a minimal RCvalue of 100 mΩcm2. Our optimized silicon surface pre-treatment in combination with the adapted PEDOT:PSS blendare successfully implemented into a cell process with the PEDOT:PSS layer located at the rear surface (the so-called 'BackPEDOT concept'). Record-high efficiencies of 18.3% and of 20.6% are achieved onn-type silicon and onp-type silicon wafers, respectively. Finally, we compare the internal quantum efficiency of our champion BackPEDOT solar cell with that of a state-of-the-art Al2O3/SiNx-passivated PERC solar cell.