Effect of Monovalent Metal Iodide Additives on the Optoelectric Properties of Two-Dimensional Sn-Based Perovskite Films

Abstract

The application of organic–inorganic perovskites has recently attracted increasing interest due to their excellent optoelectronic properties. As an emerging semiconductor, the doping capability and efficiency of these materials require further clarification but have rarely been studied previously. In this study, diverse monovalent cations, Cu+, Na+, and Ag+, are incorporated into phenethylammonium tin iodide ((PEA)2SnI4) perovskite, and the resultant lattice structural variation, film properties, and thin-film transistor performance are systematically investigated by combining theoretical and experimental methods. Owing to their unique composition and octahedral unit, perovskite semiconductors possess strong ‘substitution doping tolerance’ with the aliovalent cation dopants. Theoretical studies claim that the hypothetical monovalent cation substitution on the Sn2+ B-site creates undesired vacancies and destabilizes the perovskite lattice structure. The experimental results show that the incorporated foreign aliovalent cations are not doped inside the perovskite lattice but segregated along the grain boundaries. Benefiting from the excellent hole transport property and passivation effect of copper iodide (CuI), the CuI–(PEA)2SnI4 heterostructure composite channel layers exhibit much improved film properties and device performance, including doubled field effect mobility, compared with the pristine ones.

Doping of Sn-based two-dimensional perovskite semiconductor for high-performance field-effect transistors and thermoelectric devices

“…To further understand the effect of SnI 4 on film structure, we used X-ray diffraction (XRD) to probe the film crystallinity. As shown in Figure 2 G, XRD patterns of pristine and doped (PEA) 2 SnI 4 films show similar diffraction peaks, which are assigned to the strong (0 0 l ) ( l = 2, 4, 6, 8, 10, 12, 14) diffractions at 5.5°, 10.9°, 16.4°, 21.9°, 27.4°, 33.0°, and 38.7°, respectively, indicating a layered structure of the films ( Reo et al., 2021 ; Zhu et al., 2020a ). However, the full width at half maximum (FWHM) of (0 0 2) peaks are found to be 0.197°, 0.183°, and 0.182° for pristine, 1 mol %, and 5 mol % SnI 4 -doped films, respectively.…”

“…The electrical conductivity of the pristine film is 2.6 × 10 −6 S cm −1 , and it is enhanced as the doping ratio increases, reaching a maximum value of 2.1 × 10 −1 S cm −1 at the doping ratio of 30 mol %, which is direct evidence showing the doping effect of SnI 4 on (PEA) 2 SnI 4 perovskite. It should be mentioned that extra I − was also introduced into the films together with Sn 4+ , and I − was reported to greatly improve the charge transport property of (PEA) 2 SnI 4 by compensating the iodine vacancies (V I ), which behave as trap states ( Reo et al., 2021 ). So, it might be argued that I − may also contribute to the enhancement of conductivity in the doped (PEA) 2 SnI 4 films.…”

“…Reo et al. considered doping of (PEA) 2 SnI 4 thin films with Cu + by adding copper iodide (CuI) in the precursor solution ( Reo et al., 2021 ). It turns out that the hole transport in (PEA) 2 SnI 4 FETs gets enhanced with the incorporation of CuI.…”

“…It turns out that the hole transport in (PEA) 2 SnI 4 FETs gets enhanced with the incorporation of CuI. However, further density functional theory (DFT) calculations and X-ray diffraction (XRD) measurements reveal that the Cu + is likely distributed at grain boundaries instead of replacing the Sn 2+ within the perovskite lattices, and the improved FET performance is more likely attributed to the outstanding hole-transport property of CuI rather than doping ( Reo et al., 2021 ). These studies indicate doping can be a powerful technique to tune or enhance the performance of (PEA) 2 SnI 4 devices, but presently effective doping strategies for (PEA) 2 SnI 4 remain to be established.…”

Design and Modelling of Eco-Friendly CH3NH3SnI3-Based Perovskite Solar Cells with Suitable Transport Layers

“…Moreover, defect free crystallization of Sn-based perovskite significantly impacts cell performance. Though several efforts have been made to tackle the aforementioned issues and prevent the occurrence of defects [18][19][20][21][22][23][24][25][26][27][28], there is still ample room for improvement as the maximum efficiency (13.24%) for SnX 3 -based perovskite solar cells (PSCs) [29] and stability reached at 3800 h [30] are still lower than its SQ limit.…”