The interfacial charge transfer recombination processes under working conditions that limit the device performance in
quantum dot/polymer bulk heterojunction solar cells have been investigated. We have employed spectroscopic
techniques as charge extraction (CE), laser transient absorption spectroscopy (L-TAS) and transient photovoltage
(TPV). From the CE technique, we have observed an exponential charge accumulation in the device when light intensity
is increased, as it has been related to conventional molecular photovoltaic devices. The L-TAS showed that
recombination dynamics, in thin films, are dominated by the presence of trap in both, the nanocrystals and the polymer
materials. Finally, from the TPV experiments we observed a strong carrier lifetime, in complete devices, upon charge
density. This strong dependency of charge concentration vs charge lifetime has been found to be higher than in organic
photovoltaics based on polymer and fullerenes. The comparison between the recombination dynamics from TPV and LTAS,
performed with and without electrodes, respectively, allow us to exclude any process related with the metal
contacts in the strong dependency of the recombination with the charge density.
The combination in hybrid heterojunction of nanocrystals and semiconductor polymers has great potential for light-toenergy
conversion devices. For this reason, a great number of different quantum dots/polymer molecular solar cells have
been investigated. However, less attention has been paid to the photo-induced charge transfer processes at the interface
of these systems. Here we report a time resolved spectroscopic study of the electron injection and recombination transfer
steps of CdSe/P3HT bulk heterojunction films. From the data obtained using Time Correlating Single Photon Counting
(TCSPC) we have inferred that electron injection from P3HT excited state to CdSe nanocrystal conduction band occurs
faster than 250 ps and the electron yield is higher than 85%, independently of the nanocrystal shape. On the other hand,
the use of Laser Transient Absorption Spectroscopy allowed us to observe that all the studied interfacial charge transfer
process can be fitted to dispersive stretched exponentials kinetics, independently of the QD's concentration and
nanocrystal morphology, thereby offering evidence of multiple decay process in CdSe/P3HT bulk heterojunctions.
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