Enhanced Efficiency and Stability of Perovskite Solar Cells Through Nd‐Doping of Mesostructured TiO₂

Abstract

include solar cells that make use of mesoporous TiO 2 electrodes to collect and transport the electronic charges generated in metal-organic dyes, fi rst demonstrated by O'Regan and Grätzel. [ 3 ] Since this fi rst pioneering work, the performance of dye-sensitized TiO 2 solar cells (DSSCs) improved mainly by the development of new pigments that more effectively absorb the solar light spectrum. [ 4,5 ] A recent breakthrough was the introduction of organicinorganic perovskites, which combine high light absorption with good charge transport. [6][7][8][9][10][11][12] The high perovskite conductivity enabled the exploration of new device architectures spanning from a perovskite-sensitized mesoporous TiO 2 to TiO 2 -free planar heterojunction solar cells. [ 13 ] Currently, the best performing perovskite-based solar cells (PSCs), with a certifi ed power conversion effi ciency of more than 20%, employ a thin mesoporous TiO 2 layer as electron selective contact in combination with a thick solid perovskite absorber over-layer. [ 2 ] Due to the favorable position of its conduction band (CB), a large band gap, long electron lifetimes and low fabrication costs, TiO 2 is frequently used to prepare mesoporous electrodes in several optoelectronic applications. [14][15][16][17] Nevertheless, the relatively high density of electronic trap states below the CB are a signifi cant drawback for the application of TiO 2 electrodes in solar cells. [ 18 ] Indeed, trap states may have a large infl uence on charge recombination and charge transport, which in turn infl uence the solar cell voltage and current. [19][20][21] One method to reduce the trap states in TiO 2 is doping. A wide range of doping elements have been investigated for mesoporous TiO 2 electrodes in DSSCs [ 17,[22][23][24][25][26][27] and more recently in PSCs. [28][29][30][31] Some dopants reduce the charge recombination [ 24 ] or increase electron transport in DSSCs [ 25 ] by reducing trap states below the CB. In addition to changes in the density of trap states, doping may induce a complex interplay of other effects that impact the device performance; for example, it can affect dye absorption or change the nanoparticle size and distribution and thereby the morphology of the mesostructured fi lm, leading to a changed TiO 2 -absorber interface area in DSSCs. [ 22 ] Furthermore, modifying the CB position by TiO 2 doping can either through a downward shift increase electron injection from the dye into the TiO 2 [ 26 ] or through an upward shift increase the open-circuit voltage ( V oc ). [ 27 ] These two effects however adversely affect each other. In PSCs, reduced recombination [ 28 ] and increased Block-copolymer templated chemical solution deposition is used to prepare mesoporous Nd-doped TiO 2 electrodes for perovskite-based solar cells. X-ray diffraction and photothermal defl ection spectroscopy show substitutional incorporation into the TiO 2 crystal lattice for low Nd concentration, and increasing interstitial doping for higher concentrations. Substitutional Nd-doping...

Nanoconfined Crystallization of MAPbI3 to Probe Crystal Evolution and Stability

“…47 Our findings thus indicate that the formation of pores with diameters of 20 nm or smaller in the mesoporous scaffolds should be avoided. On the other hand, MAPbI 3 itself is metastable, and the conversion of MAPbI 3 to PbI 2 upon exposure to moisture is a leading factor in the rapid degradation of PSC device performance.…”

A Ga-doped SnO2 mesoporous contact for UV stable highly efficient perovskite solar cells

“…The normalised PCE of m-TiO 2 based PSCs decreases much further and retains only 20% of the initial PCE aer 1000 hours of full spectrum illumination. The degradation of PSCs has been ascribed to several different mechanisms related to the metal oxide component, the main ones being UV-light induced desorption of O 2 from the metal oxide surface 17,18 and the photocatalytic properties of TiO 2 actively degrading the perovskite light absorber. 19,34 Aer storing the devices in the dark for 200 hours, the PCE does not recover.…”

“…16 One of the major degradation pathways in PSCs involves a rapid decrease in performance upon UV-exposure. 14,[17][18][19] This degradation is caused by both the desorption of oxygen from TiO 2 , which exposes deep trap states and worsens the electronic properties of TiO 2 (ref. 14), and the photocatalytic properties of TiO 2 , which degrade the organic components in the PSC.…”

Migration of cations induces reversible performance losses over day/night cycling in perovskite solar cells

“…3,12,13 Indeed, significant progress has been made by replacing the organic components with their inorganic counterparts and passivating the interfaces between the different layers composing the device. [13][14][15][16][17][18] Nonetheless, temperature activated formation and migration of ionic defects within the organic-inorganic ABX 3 perovskite lattice remains a potential source of instability for perovskite photovoltaics. [19][20][21][22] Halide anion (X) vacancies have been calculated to show the lowest formation energies, 23 with bromide vacancies being favoured over iodide.…”