A tin-based perovskite solar cell (TPSCs) is a special type of perovskite solar cell, based on a tin perovskite structure (ASnX3, where 'A' is a monovalent organic or inorganic cation (e.g., formamidinium (FA+), methylammonium (MA+), or cesium (Cs+)), tin is in its Sn (II) oxidation state and 'X' is a monovalent halogen anion (I−, Br−, Cl−). As a technology, tin-based perovskite solar cells are still in the research phase, and are even less-studied than their counterpart, lead-based perovskite solar cells. The corresponding perovskite solar cells (PSCs) with lead have reached a certified power conversion efficiency (PCE) of 25.2%. However, the toxic lead in perovskites has caused extensive concerns regarding to the real-life applications of PSCs. There are environmental concerns with using lead-based perovskite solar cells in large-scale applications; one such concern is that since the material is soluble in water, and lead is highly toxic, any contamination from damaged solar cells could cause major health and environmental problems. Therefore, the development of eco-friendly lead-free PSCs is highly desired and has emerged as a promising alternative to conventional lead-based perovskite photovoiltaicm, due to the reduced environmental impact and comparable performance potential. Several tin-based perovskites such as CsSnI3, MASnI3, and FASnI3 have been reported for fabricating lead-free PSCs. Recent studies highlight formamidinium tin iodide (FASnI3) as a leading candidate due to its superior optoelectronic properties and bandgap (~1.3 eV). The maximum solar cell efficiency reported and certified is 16.65% for a triple-cation, double-anion (Cs,FA,PEA)Sn(I,Br)3, 14.6% for a modified formamidinium tin triiodide-based (CH(NH2)2SnI3 or FASnI3) composition with additional NH4SCN and PEABr content, 5.73% for CH3NH3SnIBr2, 3% for CsSnI3 (5.03% in quantum dots), and above 10% for various compositions based on formamidinium tin triiodide. FASnI3 in particular may hold promise because, applied as a thin film, it appears to have the potential to exceed the Shockley–Queisser limit by allowing hot-electron capture, which could considerably raise the efficiency.
Materials and structure TPSCs possess a similar crystal structure to their lead-based counterparts but face challenges related to the oxidation of Sn2+ to Sn4+, which leads to material degradation and efficiency loss. Common tin-based perovskite materials include:
FASnI3: Exhibits high photovoltaic efficiency and enhanced stability compared to MASnI3. MASnI3: Features a direct bandgap but suffers from rapid oxidation and structural instability. CsSnI3: Fully inorganic, offering greater thermal stability but lower efficiency. To mitigate these issues, researchers have explored mixed-cation compositions (e.g., FA/Cs blends) and surface passivation strategies incorporating reducing agents like SnF2 to suppress oxidation. Recent studies also suggest that doping with elements such as germanium (Ge) can enhance structural stability and charge carrier transport properties.
Bandgap Tunability and Alloying Effects The bandgap of TPSCs can be tuned by incorporating mixed halides (e.g., I−/Br− blends) or alloying with Ge or Pb, influencing absorption properties and energy conversion efficiency. Recent studies indicate that bandgap engineering can optimize carrier transport properties and reduce recombination losses, leading to better performance in multi-junction solar cell architectures. Additionally, studies demonstrate that reducing energy-level mismatch in formamidinium tin iodide perovskites significantly improves carrier transport and efficiency.
Enhance stability
Stability and Degradation Mechanisms The primary limitation of TPSCs is their inherent instability, particularly due to the oxidation of Sn2+ to Sn4+, which creates defects and increases charge recombination. Solar cell stability is critical to practical applications especially for outdoor photovoltaic modules that are expected to be used for tens of years. The stability of Sn-based PSCs is greatly dependent on the fabrication pro-cess and perovskite composition. Tin-based perovskites have the potential to outperform the PCE and stability of lead-based perovskite solar cells. There are lots of ways to enhance the stability. Several experimental and simulation studies have predicted that the addition of the cesium Cs + can enhance the thermodynamic structural stability of FASnI3, prevent Sn2+ oxidation, and increase geometric symmetry. Research from Marshall et al. has improved the stability and efficiency of PSCs without a hole-selective interfacial layer. Next, by alloying Ge (II) in CsSnI3 to develop a CsSn0.5Ge0.5I3 composition perovskite, thin films of CsSnI3-based PSCs can become very stable and air tolerant. Qiu et al. also suggested creating high-quality B-γ CsSnI3 thin films with a two-step sequential deposition process. Furthermore, to overcome the difficulty of large-scale manufacturing, several researchers have focused on refining deposition techniques and enhancing perovskite nano crystals or perovskite ink. The solvent SnI2 is also one of the additives commonly used in Sn-based alloys to reduce the impurity of the Sn source. The charge transport in the 2D perovskite caused the efficiency to decrease, so a 3D precursor was introduced to develop 2D/3D mixed Sn-based perovskites to obtain far better performance and stability than pure quasi2D perovskites.
Antioxidant additives: Incorporation of SnF2 and pyrazine to maintain Sn2+ stability and limit oxidation. Encapsulation techniques: Protective barrier layers prevent moisture and oxygen penetration, prolonging device longevity. Mixed-Cation formulations: Combining FA, MA, and Cs enhances structural robustness and mitigates phase instability. Gradient doping strategies: Recent research has demonstrated that introducing Ge or other dopants improves charge separation and enhances stability.
Advanced Interface Optimization and Defect Passivation New buffer layers and defect passivation techniques have been developed to suppress surface and grain boundary defects, enhancing carrier mobility and stability. Self-assembled monolayers (SAMs) and organic-inorganic hybrid interfacial coatings have shown promise in improving charge transport efficiency. Furthermore, study reported that using fullerene-based passivation layers enhances device efficiency and prevents degradation, making TPSCs more stable for long-term use.
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