Quantum dot-nanocarbon based hybrid solar cells with improved long-term performance

In this work, the development of room-temperature solution-processed hybrid solar cells based on CdSe Quantum Dots (QDs) and carbon nanomaterials are reported; multi-walled nanotubes (MWCNT) and reduced graphene oxide (rGO) are incorporated into the photoactive layer of conjugated polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)], (PCPDTBT) and CdSe QDs. Incorporation of nanocarbon materials helps to improve the long-term efficiency of the solar cells in respect of power conversion efficiency (PCE) and short-circuit current density (Jsc) compared to QDs only based devices. For the formation of the hybrid photoactive film hexadecylamine (HDA)/trioctylphosphine oxide (TOPO) capped CdSe QDs were attached to multi-walled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) by engineering the interface by introducing thiol functional groups in order to attach CdSe QDs. Initial PCE values of about 2% under AM1.5G illumination have been achieved for these hybrid nanocarbon-CdSe QDs photovoltaic devices. Furthermore, the long term stability of the photovoltaic performance of the devices was investigated and found superior compared to CdSe QDs only based devices. About 84% of the original PCE remained after storage in a glove box for one year without any further encapsulation. It is assumed that the improvement is mainly due to the thiol-functionalization of the nanocarbon interface leading to a strong binding of CdSe QDs resulting in an improved preservation of the nanomorphology of the hybrid film over time.