Electron and hole transfer at metal oxide/Sb2S3/spiro-OMeTAD heterojunctions

Abstract

Antimony sulfide has recently demonstrated huge potential as an absorber material in solid-state semiconductor-sensitised solar cells (SSSCs). Here, we present a transient absorption spectroscopy study of the TiO₂/Sb₂S₃/spiro-OMeTAD heterojunctions to elucidate the key factors influencing charge photogeneration. Efficient device performance requires that photoresponse extends into the near-infrared, yet we find that the efficiency of charge separation at the TiO₂/Sb₂S₃ interface decreases significantly as increasingly red-absorbing Sb₂S₃ nanocrystals are photoexcited. However, the efficiency of hole transfer to spiro-OMeTAD appears much less sensitive to shifts in the Sb₂S₃ absorption edge and we also observe hole transfer to spiro-OMeTAD occurring on ZrO₂ substrates, where electron injection does not occur. These observations may point to the importance of the hole transfer reaction not simply as a means of regenerating the sensitiser, but rather as an integral part of the charge separation process in Sb₂S₃ SSSCs. The present findings should help inform strategies aimed at further increasing the efficiency of nanocrystal sensitized solar cells.