Lead and HTM Free Stable Two‐Dimensional Tin Perovskites with Suitable Band Gap for Solar Cell Applications

Abstract

Organic‐inorganic hybrid perovskites have attracted great attention over the last few years as potential light‐harvesting materials for efficient and cost‐effective solar cells. However, the use of lead iodide in state‐of‐the‐art perovskite devices may demonstrate an obstacle for future commercialization due to toxicity of lead. Herein we report on the synthesis and characterization of low dimensional tin‐based perovskites. We found that the use of symmetrical imidazolium‐based cations such as benzimidazolium (Bn) and benzodiimidazolium (Bdi) allow the formation of 2D perovskites with relatively narrow band gaps compared to traditional ‐NH3+ amino groups, with optical band gap values of 1.81 eV and 1.79 eV for Bn2SnI4 and BdiSnI4 respectively. Furthermore, we demonstrate that the optical properties in this class of perovskites can be tuned by formation of a quasi 2D perovskite with the formula Bn2FASn2I7. Additionally, we investigate the change in band gap in the mixed Sn/Pb solid solution Bn2SnxPbx−1I4. Devices fabricated with Bn2SnI4 show promising efficiencies of around 2.3 %.

Tin Halide Perovskites: From Fundamental Properties to Solar Cells

“…It was suggested that the increased hydrogen bonding was the cause of the isotropic crystallization. [ 147 ] The effect of solvents was studied by Cao et al. by fabricating thin films from either pure DMSO or pure DMF solutions.…”

“…Reproduced with permission. [ 147 ] Copyright 2019, Wiley‐VCH. (c) n = 3 thin films using BA and MA cations deposited with pure DMSO or DMF.…”

“…Device applications that require small optical bandgaps should search for layered materials with reduced distortion of the inorganic layers, such as benzimidazolium and benzodiimidazolium with optical bandgaps of 1.81 and 1.79 eV, respectively. [147] Much like the 3D perovskites the optical bandgap can be shifted to higher energies when exchanging iodine for bromine. [95,109] This interesting feature was already observed in the early 1990s for decylammonium tin halide perovskites, shifting the emission peak from 605 to 517 nm.…”

“…It was suggested that the increased hydrogen bonding was the cause of the isotropic crystallization. [147] The effect of solvents was studied by Cao et al by fabricating thin films from either pure DMSO or pure DMF solutions. [134] Figure 21c shows that films casted from a DMSO solution resulted in layers parallel to the substrate, while deposition from a DMF solution resulted in a perpendicular growth of the layers.…”

Study on photovoltaic stability and performance by incorporating tetrabutyl phosphonium iodide into the active layer of a perovskite type photovoltaic cell

“…In the past decade, perovskite solar cells (PSCs) have attracted extensive research interest due to their simple preparation method, 1 adjustable band gap, [2][3][4] high performance, large absorption coefficient, 5,6 light weight, long carrier diffusing distance and solution processability. 7,8 The highest certied power conversion efficiency (PCE) reported for PSCs has reached 25.2% based on a simple solution process.…”