Investigating Charge Dynamics in Halide Perovskite Sensitized Mesostructured Solar Cells
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Investigating Charge Dynamics in Halide Perovskite Sensitized Mesostructured Solar Cells Andrea Listorti,*1,2 Vittoria Roiati,1,3,4 Silvia Colella,2 Edoardo Mosconi,5 Giovanni Lerario,1 Luisa De Marco,1 Aurora Rizzo,1,2 Filippo De Angelis5 and Giuseppe Gigli, 1,2,6 1Center
for Bio-Molecular Nanotechnology, Fondazione Istituto Italiano di Tecnologia, Via Barsanti, 73010 Arnesano (Lecce), Italy 2NNL − National Nanotechnology Laboratory, CNR Istituto Nanoscienze, Distretto Tecnologico, Via Arnesano 16, 73100 Lecce, Italy 3Department of Physics, Politecnico di Milano, p.zza Leonardo da Vinci 32, Milano, Italy 4Center for Nano Science and Technology@Polimi, Istituto Italiano di Tecnologia, Via G. Pascoli 70/3, 20133 Milano, Italy 5Computational Laboratory for Hybrid/Organic Photovoltaics (CLHYO), CNR-ISTM, Via Elce di Sotto 8, Perugia I-06123, Italy 6Dipartimento di Matematica e Fisica “E. De Giorgi”, Universita’ del Salento, Via per Arnesano, 73100 Lecce, Italy
ABSTRACT Charge generation and transport in CH3NH3PbI3-xClx based mesostructured solar cells are investigated. Time correlated single photon counting analysis proves highly efficient charge generation and provides insights on the structural properties of perovskite films. Photoinduced absorption and transient photovoltage analyses depict a double charge recombination dynamics suggesting the existence of two complementary paths for electron transport, involving either TiO2 and perovskite matrixes. Stark spectroscopy, a powerful tool allowing interface-sensitive analysis, is employed to prove the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer close to the oxide surface. This evidence is also confirmed by first principle DFT calculations. The existence of a structural order, promoted by specific local interactions, could be one of the decisive reasons for highly efficient carriers transport within perovskite films. INTRODUCTION The recent employment of self-assembling lead-halide hybrid perovskites in solar cell devices has been depicted as the “Next Big Thing in Photovoltaics”.[1] Perovskites strongly absorb light over a broad range, enabling the complete harvesting of a wide portion of solar spectrum in films as thin as few hundred nanometers. This is specifically beneficial when they are included in meso-structured (MS) solid-state cells, where the thickness of the mesoporous scaffold has been historically limiting light harvesting and photocurrent generation. In addition, through the perovskite matrix both electrons and holes can percolate to the contacts with a collection efficiency close to unity, giving the opportunity to largely overcome the limitations of previous device layouts. For these characteristics, perovskite solar cells have been assembled in a variety of architectures involving different preparation routes and possibly morphology of the final compounds.[2] Despite the rapid increase in efficiency associated with the evolution of this technology, many of the fundamental questions concerning
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