Speaker
Ms
ELHAM REZASOLTANI
(Montreal University)
Description
Due to the large band gap, large electron mobility and the high dielectric constant of zinc oxide (ZnO), it promises potential in organic-inorganic hybrid solar cells. However, such devices display lower efficiency compared to fully organic devices. Upon photoexcitation, excitons dissociate at the organic-inorganic interface, with the positive charge located on the organic material and the electron on the inorganic semiconductor. These are highly bound due to their mutual Coulomb interaction, and recombination of bound pairs at the interface is considered to be a significant reason for the low efficiency. One possible way to optimize the performance of the hybrid devices and limit this loss mechanism is to modify the interface of organic-inorganic materials . We report the influence of cis-bis(4,4-dicarboxy-2,2bipyridine) dithiocyanato ruthenium (II) (N3-dye) and -hexylthiophene-2- phosphonic acid (6TP) as interface modifiers on P3HT:ZnO (P3HT: Poly 3-Hexylthiophene) interfaces by studying charge dynamics in P3HT:ZnO, P3HT:ZnO-N3, P3HT:ZnO-6TP. We demonstrate an enhancement of photocurrent of P3HT:ZnO through molecular interface modification. Moreover, we identify the formation of long-lived polarons at P3HT:ZnO interface with and without interface modifiers via quasi-steady-state photo-induced absorption (PIA) spectroscopy. Furthermore, by probing the pump modulation frequency dependent PIA signal we find that P3HT:ZnO-N3 and P3HT:ZnO-6TP exhibit lower steady-state density with increasing frequency compared to P3HT:ZnO, while the significant difference lies in an effective polarons lifetime which highlights the importance of the molecular interface modification.
To estimate an average lifetime for long-lived polarons, we performed the pump intensity dependence of the PIA signal as well. The experimental results together with a theoretical model reveal that the average lifetime becomes longer after interface modification by over a factor of two. In other words, the interface modification causes the polarons' average lifetime to be slower, that is the significance of a slowing recombination and a more stable charge separation and transfer.
Primary author
Ms
ELHAM REZASOLTANI
(Montreal University)
Co-authors
Dr
CARLOS SILVA
(Montreal University)
Dr
IAN G. Hill
(Dalhousie University)
Dr
MINGQING WANG
(Dalhousie University)
