Combined Experimental and Simulation Studies of Lithium and Cobalt‐Modified TiO₂ and Their Impacts on the Performance and Stability of Perovskite Solar Cells

Abstract

Posttreatment of titanium oxide (TiO 2 ) using lithium (Li) and cobalt (Co) precursors is widely adopted to modify the charge quenching property in perovskite solar cells (PSCs); however, the fundamental understanding of the effect of the modification layer on the material itself and, consequently, the photovoltaic performance stability is not complete. In this work, in situ X-ray diffraction measurements show that the Li and Co ions can diffuse into TiO 2 and consequently accelerate the rutile phase transformation. X-ray photoelectron spectroscopy results reveal the appearance of a Ti 3+ feature in both the Li-and Co-treated samples, suggesting that the treatment ions are partially located at the subsurface/surface of the spin-cast TiO 2 layer. The Li-treated TiO 2 exhibits greatly upshifted conduction band edges, which benefits charge extraction properties and improves the average device parameters in a complete PSC. To complement the experiments, density functional theory calculations are performed. While Li treatment initially results in enhanced electronic properties, Li-treated TiO 2 tends to have more surface vacancies over time and is more susceptible to adsorption and accumulation of iodide ions compared to the Co-treated sample, which is experimentally supported by surface photovoltage spectroscopy and timeresolved photoluminescence results.

A simple strategy to obtain graphitic carbon nitride modified TiO2 layer for efficient perovskite solar cells

“…Metal ion-doping is a common method for increasing the electrical conductivity of TiO 2 and regulating its energy level structure [4,10]. Different metal ion-doped TiO 2 materials, including niobium (Nb) [11,12], yttrium (Y) [13], magnesium (Mg) [14,15], cobalt (Co) [16], tin (Sn) [17], tantalum (Ta) [18], and lithium (Li) [4], have been utilized to enhance the PCE of PSCs.…”

Enhancing Perovskite Thin Films with Butylammonium Iodide-Lead-Tetrahydrofuran: Surface Healing and 2D Formation in Annealing-Free Single-Crystal Films for Solar Cell Applications

“…Different equipment and methods might lead to varied energy resolutions and limitations, thereby affecting the observed E cutoff . The valence band minimum (VBM) can be estimated using eq : , VBM = 60.00 eV − E cutoff + E onset In this study, a radiation energy of 60 eV was employed. The value of E onset was found to be 1.47 eV for 3D-MAPbI 3 and 2D-capped 3D-MAPbI 3 , while the E onset value was 1.33 eV for BAI-modified 3D-MAPbI 3 .…”

“…Different equipment and methods might lead to varied energy resolutions and limitations, thereby affecting the observed E cutoff . The valence band minimum (VBM) can be estimated using eq 3: 47,49…”

“…(f) PES spectra of the secondary electron cutoff edge (E cutoff ) of samples described in panel g. (g) Energy diagram of all layers in the fabricated PSCs. The work functions of the FTO and Ag electrodes and onset CBM value were obtained from our previous work 47. Noted that the perovskite layer was prepared on an FTO/cp-TiO 2 / mp-TiO 2 substrate.…”

“…The initial phase, related to τ 1 , was predominantly influenced by rapid electron migration from the perovskite to a quenching layer. In contrast, the subsequent phase, associated with τ 2 , was governed by interfacial and/or internal recombination within the perovskite. , Figure d shows the TRPL decay characteristics of 3D-MAPbI 3 samples with and without BAI modification and the 2D capping layer deposited on the cp-TiO 2 /mp-TiO 2 substrate. With the incorporation of BAI and the 2D layer, the sample demonstrated considerably quenched intensity, indicating efficient charge extraction at the interface.…”