Raphael Caface 1 , Yuri Pusep 1 , Francisco Eduardo Guimaraes 1
1 Instituto de Física de Sao Carlos University of Sao Paulo Sao Carlos Brazil
Hybrid photovoltaic devices (HPD) based on conjugated polymers and inorganic semiconductors are being used in recent years to produce solar cells at a low cost. Therefore, efficient HPD requires efficient exciton dissociation and charged carrier collection. The present studies we demonstrated that the hybrid system formed by cylindrical radial heterostructured nanowires (NWs) covered with a thin conjugated polymer can a very suitable candidate to an efficient HPD. NWs with high density were manufactured by Molecular Beam Epitaxy (MBE) and consist of structured GaAs/Al0.3Ga0.7As/GaAs  wires covered with a thin polymer film based on poly-phenylene vinylene (PPV) deposited by the Layer-by-Layer (LbL) methodology, which favors the light absorption in the visible and in the infrared range. The core/inner and shell/outer layer configuration of NWs produces a built-in electric field that favors spatial separation of the photoexcited electrons in the core and holes in the shell. Time resolved spectroscopy shows that excitons generated in PPV are efficiently transferred to the NW at the interface. Decay time measurements show a strong dependence of the exciton lifetime in the NWs on the emission wavelength, which is associated with bottleneck effects due to tunneling limiting recombination processes in the inner AlGaAs barrier and with energy distribution of emissive states along the radial axis. Temperature dependent measurements involving NW emissions provide strong experimental evidence that the impurity binding energy varies with the radial direction, which produces a strong electric potential modulation. This effect enhances electron and hole separation and the charge transfer process at the PPV/NW interface. The conditions for efficient charge separation between the polymer and heterostructured NWs and the additional benefits of this hybrid organic/NW will be discussed.
References:  CAFACE, R. A. et al. Photoluminescence of radial GaAs/AlGaAs/GaAs nanowires. Journal of Applied, v.113, n.3, p.064315, 14 fev. 2013.