Stark Effect in Perovskite/TiO₂ Solar Cells: Evidence of Local Interfacial Order

Abstract

To unveil the mechanisms controlling photovoltaic conversion in high-performing perovskite-based mesostructured solar cells, we focus on the key role played by the mesoporous oxide/perovskite interface. We employ several spectroscopic techniques to design a complete scenario and corroborate our results with first principle density functional theory calculations. In particular 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. 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.

Time-resolved fluorescence anisotropy study of organic lead halide perovskite

“…The anisotropic behavior of the perovskite dielectric response has been theoretically confirmed previously [20]. The behavior is ascribed to the existence of oriented permanent dipoles close to the perovskite/oxide interface [21], and spontaneous electric polarization in hybrid halide perovskite [22]. Furthermore, the presence of hysteresis in the current-voltage characteristic is sometimes attributed to the reorientation of the permanent dipoles CH 3 NH 3 þ and ferroelectric domains with the applied electric field in addition to the resistance of PbI 3 À lattice [23][24][25][26].…”

Charge Accumulation and Hysteresis in Perovskite‐Based Solar Cells: An Electro‐Optical Analysis

“…[ 33,34 ] Figure 5 a displays the PIA signal of a mesoscopic device in the visible range at open-circuit and at a bias V = 0.8 V. The positive signal (Δ T / T > 0, where Δ T is the differential transmission change and T is the transmission) arising from the transitions between the fi rst valence band (VB1) to the conduction band (CB) of MAPbI 3 perovskite. [ 8 ] The magnitude of the positive signal is proportional to the bulk carrier concentration and is related to the charge carrier transport and recombination in the devices.…”

Optoelectronic Studies of Methylammonium Lead Iodide Perovskite Solar Cells with Mesoporous TiO2: Separation of Electronic and Chemical Charge Storage, Understanding Two Recombination Lifetimes, and the Evolution of Band Offsets during J–V Hysteresis

“…The shift may be related to the aligned dipoles found in some modeling of the TiO 2 /MAPI interface. 43 More certain assignment must await further evidence. …”