All-inorganic Sn-based Perovskite Solar Cells: Status, Challenges, and Perspectives

All-Inorganic Tin-Containing Perovskite Solar Cells: An Emerging Eco-Friendly Photovoltaic Technology

All-inorganic tin (Sn)-containing perovskites have emerged as highly promising photovoltaic materials for single-junction and tandem perovskite solar cells (PSCs), owing to their reduced toxicity, optimal narrow bandgap, and superior thermal stability. Since their initial exploration in 2012, significant advancements have been achieved, with the highest efficiencies of single-junction and tandem devices now surpassing 17% and 22%, respectively. Nevertheless, the intrinsic challenges associated with the oxidation susceptibility of Sn2+ and the uncontrolled crystallization dynamics impede their further development. Addressing these issues necessitates a comprehensive and systematic understanding of the degradation mechanisms inherent to all-inorganic Sn-containing perovskites, as well as the development of effective mitigation strategies. This review provides a detailed overview of the research progress in all-inorganic Sn-containing PSCs, with a particular focus on the basic properties and degradation pathways of both pristine Sn and mixed Sn-Pb perovskites. Furthermore, various strategies to improve the efficiency and stability of Sn-containing PSCs are thoroughly discussed. Finally, the existing challenges and perspectives are provided for further improving the photovoltaic performance of eco-friendly PSCs.

Prediction of ternary alkaline-earth metal Sn(II) and Pb(II) chlorides with potential applications as p-type transparent conductors

Non-metallic Sn(II) and Pb(II) compounds, particularly those with p-type properties, are essential functional materials due to their notable electronic arrangement and chemical characteristics. The presence of additional Sn(II) and Pb(II) chlorides is suggested by the existence of known Sn(II) and Pb(II) compounds. By utilizing first-principles calculations and swarm intelligence structure search techniques, we have predicted the existence of up to seven new ternary alkaline-earth metal chlorides: ABCl4 (where A = Sr and B = Sn or Pb) and AB2Cl6 (where A = Mg, Ca, or Ba and B = Sn, or A = Ca or Sr and B = Pb). These seven chlorides are in the divalent state. The interaction between Sn-5s (or Pb-6s) and Cl-3p in these compounds creates an anti-bonding effect in the upper valence bands, which enhances defect tolerance and promotes high p-type conductivity. These stable chlorides exhibit notable electronic properties, including wide band gaps ranging from 3.91 to 4.94 eV, broad hole effective masses ranging from 0.93 to 5.62 m0, and high valence band alignments ranging from 6.83 to 8.38 eV under vacuum. In particular, Ca/BaSn2Cl6 and CaPb2Cl6 have the potential to be used as p-type transparent conductors due to their favorable properties, including a lower hole effective mass (0.93 m0 for CaPb2Cl6) and higher ionization potentials (6.83/7.05 eV for Ba/CaSn2Cl6). Furthermore, the predicted CaPb2Cl6 crystal exhibits attenuated negative linear compressibility and negative zero-linear-compressibility along the c-axis in different pressure ranges due to its wine-rack structure. This report highlights potential applications for alkaline-earth metal Sn(II) and Pb(II) chlorides, including their use as transparent conductors, particularly p-type conductors.

Investigation of perovskite materials for solar cells using scanning tunneling microscopy

The issue of energy scarcity has become more prominent due to the recent scientific and technological advancements. Consequently, there is an urgent need for research on sustainable and renewable resources. Solar energy, in particular, has emerged as a highly promising option because of its pollution-free and environment-friendly characteristics. Among the various solar energy technologies, perovskite solar cells have attracted much attention due to their lower cost and higher photoelectric conversion efficiency (PCE). However, the inherent instability of perovskite materials hinders the commercialization of such devices. The utilization of scanning tunneling microscopy/spectroscopy (STM/STS) can provide valuable insights into the fundamental properties of different perovskite materials at the atomic scale, which is crucial for addressing this challenge. In this review, we present the recent research progress of STM/STS analysis applied to various perovskites for solar cells, including halide perovskites, two-dimensional Ruddlesden-Popper perovskites, and oxide perovskites. This comprehensive overview aims to inspire new ideas and strategies for optimizing solar cells.

High defect tolerance β-CsSnI3 perovskite light-emitting diodes

All-inorganic lead-free CsSnI3 has shown promising potential in optoelectronic applications, particularly in near-infrared perovskite light-emitting diodes (Pero-LEDs). However, non-radiative recombination induced by defects hinders the optoelectronic properties of CsSnI3-based Pero-LEDs, limiting their potential applications. Here, we uncovered that β-CsSnI3 exhibits higher defect tolerance compared to orthorhombic γ-CsSnI3, offering a potential for enhancing the emission efficiency. We further reported on the deposition and stabilization of highly crystalline β-CsSnI3 films with the assistance of cesium formate to suppress electron-phonon scattering and reduce nonradiative recombination. This leads to an enhanced photoluminescence quantum yield up to ∼10%. As a result, near-infrared LEDs based on β-CsSnI3 emitters are achieved with a peak external quantum efficiency of 1.81% and excellent stability under a high current injection of 1.0 A cm-2.

Theoretical Study and Analysis of CsSnX3 (X = Cl, Br, I) All-Inorganic Perovskite Solar Cells with Different X-Site Elements

In this research, SCAPS-1D simulation software (Version: 3.3.10) was employed to enhance the efficiency of CsSnX3 (X = Cl, Br, I) all-inorganic perovskite solar cells. By fine-tuning essential parameters like the work function of the conductive glass, the back contact point, defect density, and the thickness of the light absorption layer, we effectively simulated the optimal performance of CsSnX3 (X = Cl, Br, I) all-inorganic perovskite solar cells under identical conditions. The effects of different X-site elements on the overall performance of the device were also explored. The theoretical photoelectric conversion efficiency of the device gradually increases with the successive substitution of halogen elements (Cl, Br, I), reaching 6.09%, 17.02%, and 26.74%, respectively. This trend is primarily attributed to the increasing size of the halogen atoms, which leads to better light absorption and charge transport properties, with iodine (I) yielding the highest theoretical conversion efficiency. These findings suggest that optimizing the halogen element in CsSnX3 can significantly enhance device performance, providing valuable theoretical guidance for the development of high-efficiency all-inorganic perovskite solar cells.

Breaking the bottleneck of lead-free perovskite solar cells through dimensionality modulation

The emerging perovskite solar cell (PSC) technology has attracted significant attention due to its superior power conversion efficiency (PCE) among the thin-film photovoltaic technologies. However, the toxicity of lead and poor stability of lead halide materials hinder their commercialization. In this case, after a decade of effort, various categories of lead-free perovskites and perovskite-like materials have been developed, including tin halide perovskites, double perovskites, defect-structured perovskites, and rudorffites. However, the performance of the corresponding devices still falls short of expectations, especially their PCE. The limitations mainly originate from either the unstable lattice structure of these materials, which causes the distortion of their octahedra, or their low dimensionality (e.g., structural and electronic dimensionality)-correlated poor carrier transport and self-trapping effect, accelerating nonradiative recombination. Therefore, understanding the relationship between the structures and performance in these emerging candidates and leveraging these insights to design or modify new lead-free perovskites is of great significance. Herein, we review the variety of dimensionalities in different categories of lead-free perovskites and perovskite-like materials and conclude that dimensionality is an important aspect among the crucial indexes that determine the performance of lead-free PSCs. In addition, we summarize the modulation of both structural and electronic dimensionality, and the corresponding enhanced optoelectronic properties in different categories. Finally, perspectives on the future development of lead-free perovskites and perovskite-like materials for photovoltaic applications are provided. We hope that this review will provide researchers with a concise overview of these emerging materials and help them leverage dimensionality to break the bottleneck in photovoltaic applications.

Environmentally Compatible Lead-Free Perovskite Solar Cells and Their Potential as Light Harvesters in Energy Storage Systems

Next-generation renewable energy sources and perovskite solar cells have revolutionised photovoltaics research and the photovoltaic industry. However, the presence of toxic lead in perovskite solar cells hampers their commercialisation. Lead-free tin-based perovskite solar cells are a potential alternative solution to this problem; however, numerous technological issues must be addressed before the efficiency and stability of tin-based perovskite solar cells can match those of lead-based perovskite solar cells. This report summarizes the development of lead-free tin-based perovskite solar cells from their conception to the most recent improvements. Further, the methods by which the issue of the oxidation of tin perovskites has been resolved, thereby enhancing the device performance and stability, are discussed in chronological order. In addition, the potential of lead-free tin-based perovskite solar cells in energy storage systems, that is, when they are integrated with batteries, is examined. Finally, we propose a research direction for tin-based perovskite solar cells in the context of battery applications.