Mixing of Azetidinium in Formamidinium Tin Triiodide Perovskite Solar Cells for Enhanced Photovoltaic Performance and High Stability in Air

Abstract

Overcoming the issue of the stability of tin‐based perovskites is a major challenge for the commercial development of lead‐free perovskite solar cells. To attack this problem, a new organic cation, azetidinium (AZ), is incorporated into the crystal structure of formamidinium tin triiodide (FASnI3) to form the mixed‐cation perovskite AZxFA1‐xSnI3. As AZ has a similar size to FA but a larger dipole moment, hybrid AZxFA1‐xSnI3 films exhibit variation in optical and electronic properties on increasing the proportion of AZ. Trifluoromethylbenzene (CF3C6H5) serves as antisolvent to fabricate smooth and uniform perovskite films for the devices with an inverted planar heterojunction structure. The device performance is optimized to produce the greatest efficiency at x=0.15 (AZ15), for which a power conversion efficiency of 9.6 % is obtained when the unencapsulated AZ15 device is stored in air for 100 h. Moreover, the device retains 90 % of its initial efficiency for over 15 days. The significant performance and stability of this device reveal that the concept of mixed cations is a promising approach to stabilize tin‐based perovskite solar cells for future commercialization.

Femtosecond Exciton and Carrier Relaxation Dynamics of Two-Dimensional (2D) and Quasi-2D Tin Perovskites

“…As a consequence, the overlap between the two orbitals also decreases. 17,18 To obtain the greatest power conversion efficiencies (PCEs) from a 3D Sn PSC, purification of Sn precursors, 19,20 complexation of Sn precursors with dimethyl sulfoxide, 20−22 two-step crystallization, 23,24 additives, 25−28 and mixed cationic structures 29,30 were reported for preparations of Sn perovskite thin-film samples.…”

“…Time-dependent density functional theory calculations indicate that LUMO levels of the A-site cation lie above the conduction band minima acting as carrier traps for perovskite materials. 50 A-Site cation blending with additives such as EDAI 2 25 and co-cations such as guanidinium, 30 azetidinium, 29 and phenylhydrazinium thiocyanate 51 show passivation effects with enhanced carrier lifetimes. The effect of surface passivation might induce shifting of LUMO levels of hybridized organic cations, which can scavenge surface charge carriers.…”

“…The use of LD structures such as 2D and quasi-2D phases in tin perovskite solar cells (PSCs) has proven to be advantageous as they can enhance their stability through passivating the Sn vacancies and suppressing the self-doping due to oxidation of Sn 2+ to Sn 4+ , an enduring problem in three-dimensional (3D) Sn PSCs. ,,− The reasons for Sn vacancies and self-oxidation of Sn atoms were explained as being due to a strong antibonding coupling between Sn (5s) and I (6p) orbitals, which is weaker in LD structures because orbitals are localized through confinement effects. As a consequence, the overlap between the two orbitals also decreases. , To obtain the greatest power conversion efficiencies (PCEs) from a 3D Sn PSC, purification of Sn precursors, , complexation of Sn precursors with dimethyl sulfoxide, − two-step crystallization, , additives, − and mixed cationic structures , were reported for preparations of Sn perovskite thin-film samples.…”

Interfacial Engineering with a Hole-Selective Self-Assembled Monolayer for Tin Perovskite Solar Cells via a Two-Step Fabrication

“…Tin perovskites possess abundant defect states and shallow energy levels (e.g., by 0.2–0.6 eV for VBM and 0.5–0.7 eV for CBM) . Central to precedented research is protecting perovskites against Sn 2+ oxidation to defective Sn 4+ through exploring various additives, − cations, − alloying, or (pseudo)­halides , and through retarding their rapid crystallization with additives or through a solvent-mediated intermediate (e.g., a tin iodide (SnI 2 )–dimethyl sulfoxide (DMSO) complex). , In contrast, little research has been reported on replacing of hole- or electron-transport material (represented by HTM or ETM, respectively) with novel materials to enhance further the rate of charge transport to improve the PCE. It is worth noting that upon applying an indene-C 60 bisadduct (ICBA) to replace conventional C 60 serving as ETM, the photovoltage of the device was significantly enhanced by as much as 0.3 V for a tin PSC .…”

Multivariate Analysis of Mixed Ternary and Quaternary A-Site Organic Cations in Tin Iodide Perovskite Solar Cells

“…Organic–Inorganic hybrid lead halide perovskite solar cells (Pb-PSCs) have attracted considerable attention as low-cost, lightweight, and versatile next-generation solar cells, − and their power conversion efficiencies (PCEs) have been increased to more than 25% in the past decade. , Nonetheless, the use of hazardous Pb is a significant concern in commercialization, and it drove the development of Pb-free PSCs, in particular, Sn-based PSCs (Sn-PSC). , Moreover, the band gaps ( E g = 1.2–1.4 eV) of tin perovskites (ASnI 3 , where A is an organic and/or inorganic cation and I is an iodide anion) are narrower than those of their lead counterparts ( E g = 1.5–2.3 eV); therefore, tin perovskites can be used to fabricate PSCs that can approach the Shockely–Queisser limit . However, the PCEs of Sn-PSCs have only reached 10–14% (Figure S1), − because of poor film quality and the intrinsically unstable Sn 2+ ions, which easily oxidize to Sn 4+ ions and cause hole doping and shortening of the diode circuits. , These shortcomings have been partially addressed by using multiple A-site cations, such as metylammonium (MA), ,, formamidinium (FA), − guanidinium (GA), , phenylethylammonium (PEA), − and azetidinium, adding reduction agents such as SnF 2 and hydrazine, ,,,,,, surface passivation,…”