Thiolated Carbon Nanotubes/CdSe Quantum Dot Based Hybrid Solar Cells with Improved Long-Term Stability

Abstract

In this work, the development of room-temperature solution-processed hybrid solar cells based on carbon nanotubes (CNT) - CdSe quantum dot (QD) hybrid material incorporated into a 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, has been demonstrated. Incorporation of multi walled CNTs 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 QD only based devices. For the formation of the hybrid material hexadecylamine (HDA)/ trioctylphosphine oxide (TOPO) capped CdSe QDs were attached to CNTs by engineering the interface between CNTs and CdSe QDs by introducing thiol functional groups to CNTs. Initial PCE values of about 1.9 % under AM1.5G illumination have been achieved for this hybrid CNT-CdSe photovoltaic device. Furthermore, the long term stability of the photovoltaic performance of the devices was investigated and found superior to CdSe QD only based devices. About 90 % of the original PCE remained after storage in a glove box for almost one year without any further encapsulation. It is assumed that the improvement is mainly due to the thiol-functionalization of the CNT interface leading to a strong binding of CdSe QDs and a resulting preservation of the nanomorphology of the hybrid film over time.