Annealing effects on interdiffusion in layered FA-rich perovskite solar cells

Abstract

Annealing is one of the processing methods that are used for the fabrication of defect-free, photoactive perovskite films with compact grains in highly efficient and stable perovskite solar cells (PSCs). Thus, the annealing temperature is a key parameter for the control of the interdiffusion (of constituent elements) in photoactive films. In this paper, we present the results of a systematic study of the effects of annealing on the interdiffusion of constituent elements in efficient formamidinium-based PSCs. We also explore the effects of annealing-induced interdiffusion on layer microstructures, local strains, and the optoelectronic properties of perovskite films. We observe a dramatic upward diffusion of tin (Sn) and titanium (Ti) from fluorine-doped tin oxide and titanium dioxide (TiO2) to the perovskite films. We also observe a downward diffusion of lead (Pb) and iodine (I) from the perovskite films to the mesoporous layer of the electron transporting layer (ETL), after annealing at temperatures between 100 and 150 °C. The diffused I substitutes for Ti in the ETL, which improves the optoelectronic properties of the films, for annealing temperatures between 100 and 130 °C. The annealing-induced interdiffusion that occurs at higher temperatures (between 140 and 150 °C) results in higher levels of interdiffusion, along with increased local strains that lead to the nucleation of pores and cracks. Finally, the implications of the results are discussed for the design of PSCs with improved photoconversion efficiencies and stability.

Effects of polyethylene oxide particles on the photo-physical properties and stability of FA-rich perovskite solar cells

“…Unless otherwise stated, most of the materials used in this work were purchased from Sigma Aldrich and used as received. Apart from Polyethylene Oxide (PEO) polymer, all the other materials have been listed in our previous work on FA-Rich PSC 13 , 55 – 57 .…”

“…After sequential cleaning of pre-patterned FTO-coated glass substrate in a detergent, acetone, and IPA, a compact electron transport layer (ETL) was formed from mixed titanium dioxide (TiO 2 ) and tin (iv) oxide (SnO 2 ) precursor solutions following the procedure described elsewhere 55 . The SnO 2 and TiO 2 in the ETL precursor solution was mixed in the volume proportion of 0.2 (optimized from previous work) before being spin coated onto the FTO coated glass substrate 57 .The perovskite active layer was formed on the ETL via a two-step spin-coating process where the lead (II) Iodide (0.5993 g in 1 ml of mixed DMF-DMSO solvent) was first spin-coated, followed by the organic components that were mixed with PEO in different weight proportions.…”

“…The SnO 2 and TiO 2 in the ETL precursor solution was mixed in the volume proportion of 0.2 (optimized from previous work) before being spin coated onto the FTO coated glass substrate 57 .The perovskite active layer was formed on the ETL via a two-step spin-coating process where the lead (II) Iodide (0.5993 g in 1 ml of mixed DMF-DMSO solvent) was first spin-coated, followed by the organic components that were mixed with PEO in different weight proportions. The organic component consisted of a mixture of FAI, MACl and MABr in the ratio of 10:1:1 by mass (60 mg, 6 mg and 6 mg) respectively 13 , 55 . The weight proportion of PEO in the organic mixed precursor solution was varied from 0 wt% (control), 2 wt%, 5 wt%, and 10 wt% to study the effects of PEO weight percentage on the properties of perovskite/PEO composite films.…”

Adhesion in Perovskite Solar Cell Multilayer Structures

“…To remove residuals, pre-etched FTO-coated (∼7 Ω/sq) glass slides (MSE Supplies, AZ) were cleaned successively in Decon-90, deionized water, acetone, and isopropyl alcohol for 15 min each and treated by UV–ozone exposure (Novascan, IA, USA). A compact TiO 2 (cTiO 2 ) electron transport layer (ETL, thickness of ∼100 nm) was formed using 0.15 and 0.3 M TiO 2 solutions as described elsewhere. , A mesoporous TiO 2 (mTiO 2 ) layer was subsequently spin-coated at 4000 rpm for 30 s with titania paste in ethanol (1:5, v/v) and calcined at 500 °C for 30 min …”

Temperature Matters: Enhancing Performance and Stability of Perovskite Solar Cells through Advanced Annealing Methods

“…With the annealing of perovskite, the peak of mesophase gradually disappears, the diffraction peak of the perovskite α phase gradually increases, and the crystal orientation is obvious. Oyewole et al used scanning electron microscopy to test the surface morphologies annealed at different temperatures, as shown in Figure 14b [93], and the test results clearly showed that the annealing temperature would significantly affect the surface morphologies of perovskite films. The grain size of the perovskite film annealed at 100 • C is small, and the grain size increases with the gradual increase in temperature.…”