Making Room for Growing Oriented FASnI₃ with Large Grains via Cold Precursor Solution

Abstract

Tin halide perovskites are promising candidates for preparing efficient leadfree perovskite solar cells due to their ideal band gap and high charge-carrier mobility. However, the notorious rapid crystallization process results in the inferior power conversion efficiency (PCE) of tin perovskite solar cells (TPSCs). Here, a facile method is employed to manage this crystallization process by using cold precursor solution that raises the critical Gibbs free energy to slow down the nucleation rate, sparing both space and time for crystal growth. In this way, highly oriented FASnI 3 films with micrometer-scale grains are fabricated and an increase of 70 mV in the open-circuit voltage is obtained for TPSCs. This method is compatible with other existed strategies such as additive engineering or the post-treatment method. The best-performing device that combines 0 °C precursor solution and post-treatment method demonstrates a PCE of 12.11%.

Healing the Buried Cavities and Defects in Quasi-2D Perovskite Films by Self-Generated Methylamine Gas

“…When moving the liquefied sample away from the MA gas atmosphere, the P MA decreased to zero and the equilibrium x -value drops to be lower than 3–4 immediately, making the perovskite precursor solution highly oversaturated. As a dominating mechanism, spontaneous isotropic nucleation of perovskite would occur under this highly oversaturated condition to form a high density of seeds, resulting in perovskite films with small grains. − In the SG-MA case, the amount of MA molecules was limited by the reaction between BA and MAI (i.e., x = 0.5 in our study), which is insufficient to liquefy all the perovskite phase and probably will form only zone liquefied regions (coexisting with remaining crystal regions). In this case, the flowable liquid phases have the chance to heal the embedded cavities and gaps, probably through capillarity effect.…”

Advances and Challenges in Tin Halide Perovskite Nanocrystals

“…In the perovskite community, the investigations of some fundamental issues in terms of material chemistry and physics are intimately linked to the optoelectronic applications, either for the benchmark energy conversion efficiencies or the enhanced environmental and operational stability. Although it still remains unclear which is the best choice for devices among all-inorganic and hybrid THPs, previous experiments evidence that solar cells constructed by hybrid THPs, especially FASnI 3 or its derivatives, show much higher power conversion efficiencies than those based on CsSnX 3 . ,− It is noted that when the size of FASnI 3 NCs is down to several nanometers, in addition to the occurrence of a strong quantum-confinement effect, the conduction band can evolve from a continuous band structure to separate energy levels . This leads to slow carrier relaxation, suggesting its potential for high-efficiency photovoltaic devices that could break the Shockley–Queisser limit.…”

“…In the past decade, chemists, material scientists, and engineers have made some achievements on THPs in the form of polycrystalline films and on their related optoelectronic applications. − THP based solar cells have attained a power conversion efficiency of over 14% and are gradually narrowing the efficiency gap with Pb-based solar cells; unfortunately, the synthetic chemistry, the understanding of intrinsic physical and chemical properties, and the device applications of the THP NCs significantly lag behind those of their Pb-based counterparts. The synthesis of CsSnX 3 NCs via a hot-injection method was reported early in 2016, but the subsequent research did not spring up because of the synthetic challenge and the instability of THP lattices .…”

FA/MA Cation Exchange for Efficient and Reproducible Tin-Based Perovskite Solar Cells

“…Organic–inorganic metal halide perovskites with the generic structure of ABX 3 [A = Cs + , CH 3 NH 3 + (MA + ), and CH­(NH 2 ) 2 + (FA + ); B = Pb 2+ or Sn 2+ ; and X = I – , Br – , and Cl – ] have attracted great attention in the past decade for being used as light-absorbing materials in perovskite solar cells (PSCs). − The power conversion efficiencies (PCEs) of the state-of-art Pb-PSCs have soared rapidly from the initial 3.8% in 2009 to 25.5% in 2021, offering a promising alternative photovoltaic technology to the commercial silicon solar cells. ,, However, the toxic lead in Pb-PSCs may restrict their mass production and practical applications. Therefore, it is imperative to develop less toxic or nontoxic lead-free perovskite materials with favorable optoelectronic properties. − Sn-perovskites could be the most promising alternatives, and many efforts have been devoted to the development of Sn-PSCs in recent years. ,,− Until now, the highest PCE reported for Sn-PSCs is 14.6%, far below that of the state-of-the-art Pb-PSCs. , One of the major challenges is the oxidative instability of Sn 2+ that easily results in high defect density in perovskite films. The other is the rapid crystallization of Sn-perovskites that strongly undermines the film coverage, crystallinity, and reproducibility. − …”

“…At present, the efficient Sn-PSCs are basically composed of FASnI 3 perovskites, and most of the studies have focused on suppressing the Sn 2+ oxidation to improve the device performance via a variety of approaches including surface treatments, the use of reductants and antioxidants, composition engineering, and so forth. − ,,− Nevertheless, very few efforts have been spent on managing the film formation of the tin perovskites, which is in fact equally important to achieve good device performance. For example, the introduction of Lewis acid–base or hydrogen bonding interaction, surface-controlled growth, mixed-cation engineering, and precursor solution cooling were recently explored to retard the crystallization of FASnI 3 perovskites to produce compact and pinhole-free perovskite films with excellent photovoltaic performance. ,,,− Unfortunately, the requirement of a specific additive or the low-temperature control process makes it less attractive for the extensive applications. It is notable that the incorporation of bulky organic cations such as ethylammonium (EA + ), phenylethylammonium (PEA + ), guanidinium (GA + ), 5-ammoniumvaleric acid (5-AVA + ), and 3-phenyl-2-propen-1-amine into the FASnI 3 lattice could be an efficient way to greatly improve both the film quality and stability. ,,− However, two-dimensional (2D)/three-dimensional hybrid perovskites will form in these cases, which could reduce the light absorption of the perovskite films due to the enlarged band gaps.…”