Performance improvement of P3HT/TiO2 coaxial heterojunction polymer solar cells by introducing a CdS interface modifier

Coaxial heterojunction polymer solar cells consisting of vertical aligned crystalline TiO2 nanotube arrays transferred onto FTO-coated glass and ordered interpenetrating poly(3-hexylthiophene-2,5-diyl) (P3HT) have been fabricated through interface sensitization of CdS quantum dots on TiO2 nanotube walls. The performances of structurally identical polymer solar cells with and without CdS quantum dots sensitization were investigated and compared. The sensitized P3HT/CdS-TiO2 cell demonstrated an open-circuit photovoltage of 0.72 V and a short-circuit current of 8.29 mA/cm2 while the P3HT/TiO2 cell was 0.41 V and 5.64 mA/cm2. The efficiency of this sensitized cell represents a more than four-fold improvement compared to the non-sensitized cell. By probing the charge transport characteristics at interfaces and the mechanism of photoelectric conversion, it is found the moderately interfacial CdS QDs plays the role of assisting charge separation and suppression of back recombination at interfaces, which accounts for the observed enhanced Jsc and Voc in photovoltaic performance.