Optoelectronic Properties of Mixed Sn/Pb Perovskite Solar Cells: The Study of Compressive Strain by Raman Modes

Abstract

Mixed Sn/Pb perovskite solar cells offer a suitable alternative pathway to reduce lead toxicity and regulate optical band gap and therefore have significant potential for the development of clean and renewable energy technologies. In this study, the optical and electrical properties of CH 3 NH 3 Sn x Pb 1−x I 3 [0 ≤ x ≤ 1] solar cells under dark conditions were investigated. The compressive strain values of perovskite layers were measured and reported by analyzing the shift of their active Raman modes. Electrical characterizations under dark conditions showed that the values of the threshold voltage (V th ) and inverse saturation current (I 0 ) of the cells decrease and increase with increasing Sn concentration, respectively. Examination of the behavior of the space charge limited current (SCLC) of cells showed that the presence of Sn atoms increases the ability of the electrical carrier mobility (μ) of cells. Based on the results and calculations, the charge transport mechanism indices including the ideality factor (n), trap-filled limit voltage (V TFL ), trap-state density (n trap ), and the lifetime of minor carriers (τ n ) in each of the samples were characterized and reported.

Strain effects on halide perovskite solar cells

“…Raman spectroscopy has also been utilized to measure the residual strain of the perovskite film. 65,66 The residual strain can generate blue shift of Raman modes, thus, local strain can be evaluated by vibration frequency variations in Raman spectroscopy. For example, through the vibrational modes shift in experimental Raman spectra, Badrooj and co-workers 65 estimated the amount of compressive strain of MASn x Pb 1− x I 3 perovskite film by:where and ω 0 represent the relative shift of the Raman bands (cm −1 ) and the peak position at zero strain, respectively, γ represents the Gruneisen parameter, which can be estimated as 1.6 for polycrystalline perovskites, ν and ε z represent the Poisson ratio (average around 0.3) and the compressive strain, respectively.…”

“…For example, through the vibrational modes shift in experimental Raman spectra, Badrooj and co-workers 65 estimated the amount of compressive strain of MASn x Pb 1− x I 3 perovskite film by:where and ω 0 represent the relative shift of the Raman bands (cm −1 ) and the peak position at zero strain, respectively, γ represents the Gruneisen parameter, which can be estimated as 1.6 for polycrystalline perovskites, ν and ε z represent the Poisson ratio (average around 0.3) and the compressive strain, respectively. 65…”

“…Raman spectroscopy has also been utilized to measure the residual strain of the perovskite film. 65,66 The residual strain can generate blue shift of Raman modes, thus, local strain can be evaluated by vibration frequency variations in Raman spectroscopy. For example, through the vibrational modes shift in experimental Raman spectra, Badrooj and co-workers 65 estimated the amount of compressive strain of MASn x Pb 1Àx I 3 perovskite film by:…”

“…where Do AE o 0 and o 0 represent the relative shift of the Raman bands (cm À1 ) and the peak position at zero strain, respectively, g represents the Gruneisen parameter, which can be estimated as 1.6 for polycrystalline perovskites, n and e z represent the Poisson ratio (average around 0.3) and the compressive strain, respectively. 65 Since strain is a common attribute of ferroelastic materials, piezoresponse force microscopy (PFM) can probe the ferroic behavior and identify ferroelastic domains with spontaneous and reversible strain. 67 PFM is a variation of atomic force microscopy (AFM) measurement during which a sample surface is brought into contact with a conducting probe tip to which an alternating current (AC) is applied.…”

Optoelectronic Properties of Tin–Lead Halide Perovskites

“…Despite such discernible underlying trends, charge-carrier mobility values reported for tin iodide perovskites vary by 3 orders of magnitude between different studies, − ,,,,,,, highlighting a significant influence of extrinsic effects linked to fabrication techniques (as well as variations in measurement protocols). For such tin-rich compositions, a particularly strong influence again derives from tin vacancy formation, which, as discussed above, causes background hole densities as high as 10 17 –10 20 cm –3 .…”