title: Direct monitoring of ultrafast electron and hole dynamics in perovskite solar cells.
abstract: Organic-inorganic hybrid perovskite solar cells have emerged as cost effective efficient light-to-electricity conversion devices. Unravelling the time scale and the mechanisms that govern the charge carrier dynamics is of paramount importance for a clear understanding and further optimization of the perovskite based devices. For the classical FTO/bulk titania blocking layer/mesoporous titania/perovskite/Spiro-OMeTAD (FTO/TPS) cell, further detailed and systematic studies of the ultrafast events related to exciton generation, electron and hole transfer, ultrafast relaxation are still needed. We characterize the initial ultrafast processes attributed to the exciton-perovskite lattice interactions influenced by charge transfer to the electron and hole transporters that precede the exciton diffusion into free charge carriers occurring in the sensitizer. Time-resolved transient absorption studies of the FTO/perovskite and FTO/TPS samples under excitation at different wavelengths and at low fluence 2 (μJ cm(-2)) indicate the sub-picosecond electron and hole injection into titania and Spiro-OMeTAD, respectively. Furthermore, the power-dependent femtosecond transient absorption measurements support the ultrafast charge transfer and show strong Auger-type multiparticle interactions at early times. We reveal that the decays of the internal trap states are the same for both films, while those at surfaces differ. The contribution of the former in the recombination is small, thus increasing the survival probability of the charges in the excited perovskite.
authors.affiliation: Departamento de Química Física, Facultad de Ciencias Ambientales y Bioquímica, and INAMOL, Universidad de Castilla-La Mancha, Avenida Carlos III, S/N, 45071 Toledo, Spain. abderrazzak.douhal@uclm.es.
authors.forename: Piotr
authors.initials: P
authors.lastname: Piatkowski
authors.forename: Boiko
authors.initials: B
authors.lastname: Cohen
authors.forename: Francisco
authors.initials: F
authors.lastname: Javier Ramos
authors.forename: Maria
authors.initials: M
authors.lastname: Di Nunzio
authors.forename: Mohammad Khaja
authors.initials: MK
authors.lastname: Nazeeruddin
authors.forename: Michael
authors.initials: M
authors.lastname: Grätzel
authors.forename: Shahzada
authors.initials: S
authors.lastname: Ahmad
authors.forename: Abderrazzak
authors.initials: A
authors.lastname: Douhal