A Bifunctional Carbazide Additive For Durable CsSnI3 Perovskite Solar Cells

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.

Tuning the Crystallization and Photothermal Aging Chemistry of CsPb0.4Sn0.6I3 for Inorganic Perovskite Tandem Photovoltaics

The poor performance of inorganic narrow bandgap perovskite solar cells (PSCs) hinders the development of inorganic perovskite tandem solar cells (IPTSCs). We modulate the crystallization and photothermal aging chemistry for CsPb0.4Sn0.6I3 (1.31 eV) with guanidinoacetic acid (GCA) to develop IPTSC. The CsPb0.4Sn0.6I3:GCA PSC reaches an efficiency of 16.93% and maintains an initial efficiency of ∼80% (T80) for 1300 h under maximum power point tracking (MPPT) at 65 °C. We identify that there are not only ionic migration species (I-, I3 -) but also molecular migration species (SnI4, I2) for CsPb0.4Sn0.6I3 correlated to the photothermal dynamics. For CsPb0.4Sn0.6I3 film, the intractable pinholes accelerate the iodine migration to the electrode and photothermal degradation. The photodegradation of PbI2 produces I2 and then promotes the Sn2+ oxidation to Sn4+, causing tin migration in the form of SnI4 to accumulate at the electron transport layer/perovskite interface, and in turn generating more pinholes and Sn-Pb segregation. In CsPb0.4Sn0.6I3:GCA film, due to the coordination bonds with Pb/Sn cations and hydrogen bonds with I- ions, GCA incorporation-induced pinhole-free morphology can significantly suppress ion/molecule migration. Combined with CsPbI2Br subcell, two-terminal IPTSC delivers an efficiency of 22.18%, accompanied by T80 = 850 h under MPPT at 65 °C.

Modulated π-Bridge of Thioxothiazolidine Derivatives for Passivating Bilateral Interfaces and Grain Boundaries in n-i-p Perovskite Solar Cells

Additive engineering has emerged as the predominant approach for enhancing the performance of perovskite solar cells (PSCs). Donor-π-acceptor (D-π-A) dyes with tailored configurations have proven to be a viable and effective strategy for passivating defects and optimizing interfacial contacts. In this study, we present two asymmetrical D-π-A dyes, designated as TZR and TNR. These dyes are designed and synthesized with identical hole- and electron-transporting backbones but feature distinct π-bridge groups. They are incorporated into the precursor solution of PbI2 to facilitate in situ passivation of both interfaces and grain boundaries (GBs) during the formation of the perovskite film (two-step process). These dyes effectively penetrate both buried and upper interfaces, allowing for the passivation of defects originating from the GBs, and both interfaces. This significantly reduces defects while enhancing charge transport properties. Notably, the π-bridge composed of benzo[1,2,5]-thiadiazole in TZR contains unpaired electrons from nitrogen and sulfur atoms. An impressive power conversion efficiency (PCE) of 25.11 % is achieved. This performance significantly surpasses that of TNR-based and pristine devices, achieving PCEs of 24.47 % and 22.88 %, respectively. Furthermore, we observed a significant improvement in the stability of the unencapsulated device, attributed to the exceptional hydrophobicity of the D-π-A dyes. This study offers valuable insights into achieving high-performance PSCs through careful molecular design.

Improved Crystallinity and Defect Passivation for Formamidinium Tin Iodide-Based Perovskite Light-Emitting Diodes

The toxicity of lead (Pb) presents a critical challenge for the application of perovskite optoelectronics. In tin (Sn) perovskite, Sn2+ is easily oxidized to Sn4+ during the crystallization process. The uncontrollable oxidation process affects the crystallinity of perovskite films and leads to nonradiative traps within the films, resulting in poor device performance. Herein, we improve the efficiency of formamidinium tin iodide (FASnI3)-based perovskite LEDs (PeLEDs) through the inclusion of phenyl-thioure (PTC), which enhances crystallinity and suppresses oxidation of the Sn perovskite emitters. We achieve a high-performance near-infrared FASnI3-based PeLED with a peak external quantum efficiency (EQE) of 6.4% and a maximum radiance of 117 W sr-1 m-2. The devices exhibit operational lifetimes (T50) of ∼12.4 h under a constant current density of 10 mA cm-2, representing some of the most stable FASnI3-based PeLEDs. Our work explores a pathway for regulating crystallinity, inhibiting oxidation, and passivating defects in lead-free Sn-based PeLEDs.

Heteroatomic molecules for coordination engineering towards advanced Pb-free Sn-based perovskite photovoltaics

As an ideal eco-friendly Pb-free optoelectronic material, Sn-based perovskites have made significant progress in the field of photovoltaics, and the highest power conversion efficiency (PCE) of Sn-based perovskite solar cells (PSCs) has been currently approaching 16%. In the course of development, various strategies have been proposed to improve the PCE and stability of Sn-based PSCs by solving the inherent problems of Sn2+, including high Lewis acidity and easy oxidation. Notably, the recent breakthrough comes from the development of heteroatomic coordination molecules to control the characteristics of Sn-based perovskites, which are considered to be vital for realizing efficient PSCs. In this review, the up-to-date advances in the design of heteroatomic molecules and their key functions in the fabrication of Sn-based perovskite films are comprehensively summarized. Firstly, the design principles of heteroatomic coordination molecules and their impact on the colloidal chemistry, crystallization dynamics, and defect properties of Sn-based perovskites are introduced. Then, state-of-the-art heteroatomic coordination molecules for efficient Sn-based PSCs are discussed in terms of their heteroatom types and functional groups. Lastly, we shed some light on the current challenges and future perspectives regarding the rational design of heteroatomic coordination molecules for further boosting the performance of Sn-based PSCs.

Durable all-inorganic perovskite tandem photovoltaics

All-inorganic perovskites prepared by substituting the organic cations (for example, methylammonium and formamidinium) with inorganic cations (for example, Cs+) are effective concepts to enhance the long-term photostability and thermal stability of perovskite solar cells (PSCs)1,2. Hence, inorganic perovskite tandem solar cells (IPTSCs) are promising candidates for breaking the efficiency bottleneck and addressing the stability issue, too3,4. However, challenges remain in fabricating two-terminal (2T) IPTSCs due to the inferior film formation and deep trap states induced by tin cations5-7. Here a ligand evolution (LE) strategy with p-toluenesulfonyl hydrazide (PTSH) is used to regulate film formation and eliminate deep traps in inorganic narrow-bandgap (NBG) perovskites, enabling the successful development of 2T IPTSCs. Accordingly, the 1.31 eV CsPb0.4Sn0.6I3:LE device delivers a record efficiency of 17.41%. Combined with the 1.92 eV CsPbI2Br top cell, 2T IPTSCs exhibit a champion efficiency of 22.57% (certified, 21.92%). Moreover, IPTSCs are engineered to deliver remarkable durability under maximum power point (MPP) tracking, maintaining 80% of their initial efficiency at 65 °C for 1,510 h and at 85 °C for 800 h. We elucidate that LE deliberately leverages multiple roles for inorganic NBG perovskite growth and anticipate that our study provides an insightful guideline for developing high-efficiency and stable IPTSCs.

1.4% External Quantum Efficiency 988 nm Light Emitting Diode Based on Tin-Lead Halide Perovskite

In recent years, metal halide perovskite-based light-emitting diodes (LEDs) have garnered significant attention as they display high quantum efficiency, good spectral tunability, and are expected to have low processing costs. When the peak emission wavelength is beyond 900 nm the interest is even higher because of the critical importance of this wavelength for biomedical imaging, night vision, and sensing. However, many challenges persist in fabricating these high-performance NIR LEDs, particularly for wavelengths above 950 nm, which appear to be limited by low radiance and poor stability. In this study, 3-(aminomethyl) piperidinium (3-AMP) is employed as a bulk additive for a tin-lead halide perovskite. The 3-AMP passivated films exhibit a significantly longer carrier lifetime of over 1 µs compared to neat films (0.43 µs) or to those passivated with a perfluorinated aromatic mono-ammonium molecule (0.41 µs). Our optimized tin-lead halide perovskite-based LEDs show a single emission peak at 988 nm and an external quantum efficiency (EQE) of ≈1.4%.

Inkjet-Printed FASn1-xPbxI3-Based Perovskite Solar Cells

Metal halide perovskite solar cells (PSCs) have gained significant attention in thin-film photovoltaic research for their high power conversion efficiency (PCE) and facile fabrication processes. This study presents the use of inkjet printing to fabricate thin films of combinatorial mixed formamidinium tin-lead perovskites and evaluates their layer quality and device performance. Our findings demonstrate that incorporating Pb up to 50% into FASnI3 films enhances lattice stability. The investigation focused on optimizing the composition ratio for improved photovoltaic performance with FASn0.5Pb0.5I3-based PSCs achieving the highest PCE of 10.26%. Additionally, these cells exhibited an absorption spectrum extending beyond 1000 nm, corresponding to a 1.25 eV bandgap. The results suggest that inkjet printing can effectively enhance the efficiency of tin-lead-based PSCs, supporting scalability in device manufacturing.

Design and Simulation for Minimizing Non-Radiative Recombination Losses in CsGeI2Br Perovskite Solar Cells

CsGeI2Br-based perovskites, with their favorable band gap and high absorption coefficient, are promising candidates for the development of efficient lead-free perovskite solar cells (PSCs). However, bulk and interfacial carrier non-radiative recombination losses hinder the further improvement of power conversion efficiency and stability in PSCs. To overcome this challenge, the photovoltaic potential of the device is unlocked by optimizing the optical and electronic parameters through rigorous numerical simulation, which include tuning perovskite thickness, bulk defect density, and series and shunt resistance. Additionally, to make the simulation data as realistic as possible, recombination processes, such as Auger recombination, must be considered. In this simulation, when the Auger capture coefficient is increased to 10-29 cm6 s-1, the efficiency drops from 31.62% (without taking Auger recombination into account) to 29.10%. Since Auger recombination is unavoidable in experiments, carrier losses due to Auger recombination should be included in the analysis of the efficiency limit to avoid significantly overestimating the simulated device performance. Therefore, this paper provides valuable insights for designing realistic and efficient lead-free PSCs.

Regulating Surface Metal Abundance via Lattice-Matched Coordination for Versatile and Environmentally-Viable Sn-Pb Alloying Perovskite Solar Cells

Narrow-bandgap Sn-Pb alloying perovskites showcased great potential in constructing multiple-junction perovskite solar cells (PSCs) with efficiencies approaching or exceeding the Shockley-Queisser limit. However, the uncontrollable surface metal abundance (Sn2+ and Pb2+ ions) hinders their efficiency and versatility in different device structures. Additionally, the undesired Pb distribution mainly at the buried interface accelerates the Pb leakage when devices are damaged. In this work, a novel strategy is presented to modulate crystallization kinetics and surface metal abundance of Sn-Pb perovskites using a cobweb-like quadrangular macrocyclic porphyrin material, which features a molecular size compatible with the perovskite lattice and robustly coordinates with Pb2+ ions, thus immobilizing them and increasing surface Pb abundance by 61%. This modulation reduces toxic Pb leakage rates by 24-fold, with only ∼23 ppb Pb in water after severely damaged PSCs are immersed in water for 150 h.This strategy can also enhance chemical homogeneity, reduce trap density, release tensile strain and optimize carrier dynamics of Sn-Pb perovskites and relevant devices. Encouragingly, the power conversion efficiency (PCEs) of 23.28% for single-junction, full-stack devices and 21.34% for hole transport layer-free Sn-Pb PSCs are achieved.Notably, the related monolithic all-perovskite tandem solar cell also achieves a PCE of 27.03% with outstanding photostability.

Short-Wave Infrared Light-Emitting Diodes Using Colloidal CuInS2 Quantum Dots with ZnI2 Dual-Passivation

Short-wave infrared (SWIR) light-emitting diodes (LEDs) have emerged as promising technologies for diverse applications such as optical communication, biomedical imaging, surveillance, and machine vision. Colloidal quantum dots (QDs) are particularly attractive for SWIR LEDs due to their solution processability, compatibility with flexible substrates, and tunable absorption and luminescence. However, the presence of toxic elements or precious metals in most SWIR-emitting QDs poses health, environmental, and cost challenges. In this context, CuInS2 (CIS) QDs are known for low toxicity, cost-effective fabrication, and SWIR-light emitting capability. However, CIS QDs have not yet been directly utilized to fabricate SWIR LEDs to date, which is due to low particle stability, inefficient charge carrier recombination, and significantly blue-shifted luminescence after integrating into LED devices. To address challenges, we propose a dual-passivation strategy using ZnI2 as a chemical additive to enhance both the optical property of plain CIS QDs and charge carrier recombination upon LED device implementation. The resulting CIS-QD-based LEDs exhibit a stable SWIR electroluminescence (EL) peak (over 1000 nm) with a high EL radiance and a record external quantum efficiency in the SWIR region. Our study represents a significant step forward in SWIR-QLED technology, offering a pathway for the development of high-performance, low-cost, and nontoxic SWIR light sources.

Additive engineering via multiple-anchoring enhances 2D perovskite solar cells' performance

Passivation defects and reducing charge recombination are of great importance in enhancing 2D perovskite solar cells' (PSCs) performance. Herein, a novel additive (TEMPIC) is introduced into 2D PSCs to improve photovoltaic properties of the device, which are mainly attributed to passivated trap-states and reduced charge recombination in device.

Multifunctionally Reusing Waste Solder to Prepare Highly Efficient Sn-Pb Perovskite Solar Cells

The preparation of perovskite components (PbI2 and SnI2) using waste materials is of great significance for the commercialization of perovskite solar cells (PSCs). However, this goal is difficult to achieve due to the purity of the recovered products and the easy oxidation of Sn2+. Here, a simple one-step synthetic process to convert waste Sn-Pb solder into SnI2/PbI2 and then applied as-prepared SnI2/PbI2 to PSCs for high additional value is adopted. During fabrication, Sn-Pb waste solder is also employed to serve as a reducing agent to reduce the Sn4+ in Sn-Pb mixed narrow perovskite precursor and hence remove the deep trap states in perovskite. The target PSCs achieved an efficiency of 21.04%, which is better than the efficiency of the device with commercial SnI2/PbI2 (20.10%). Meanwhile, the target PSC maintained an initial efficiency of 80% even after 800 h under continuous illumination, which is significantly better than commercial devices. In addition, the method achieved a recovery rate of 90.12% for Sn-Pb waste solder, with a lab-grade purity (over 99.8%) for SnI2/PbI2, and the cost of perovskite active layer reduced to 39.81% through this recycling strategy through calculation.

Cyano-Coordinated Tin Halide Perovskites for Wearable Health Monitoring and Weak Light Imaging

Low-toxicity tin halide perovskites with excellent optoelectronic properties are promising candidates for photodetection. However, tin halide perovskite photodetectors have suffered from high dark current owing to uncontrollable Sn2+ oxidation. Here, 2-cyanoethan-1-aminium iodide (CNI) is introduced in CH(NH2)2SnI3 (FASnI3) perovskite films to inhibit Sn2+ oxidation by the strong coordination interaction between the cyano group (C≡N) and Sn2+. Consequently, FASnI3-CNI films exhibit reduced nonradiative recombination and lower trap density. The self-powered photodetector based on FASnI3-CNI exhibits low dark current (1.04 × 10-9 A cm-2), high detectivity (2.2 × 1013 Jones at 785 nm), fast response speed (2.62 µs), and good stability. Mechanism studies show the increase in the activation energy required for thermal emission and generated carriers, leading to a lower dark current in the FASnI3-CNI photodetector. In addition, flexible photodetectors based on FASnI3-CNI, exhibiting high detectivity and fast response speed, are employed in wearable electronics to monitor the human heart rate under weak light and zero bias conditions. Finally, the FASnI3-CNI perovskite photodetectors are integrated with a 32 × 32 thin-film transistor backplane, capable of ultraweak light (170 nW cm-2) real-time imaging with high contrast, and zero power consumption, demonstrating the great potential for image sensor applications.

Colloidal Zeta Potential Modulation as a Handle to Control the Crystallization Kinetics of Tin Halide Perovskites for Photovoltaic Applications

Tin halide perovskites (THPs) have demonstrated exceptional potential for various applications owing to their low toxicity and excellent optoelectronic properties. However, the crystallization kinetics of THPs are less controllable than its lead counterpart because of the higher Lewis acidity of Sn2+, leading to THP films with poor morphology and rampant defects. Here, a colloidal zeta potential modulation approach is developed to improve the crystallization kinetics of THP films inspired by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. After adding 3-aminopyrrolidine dihydro iodate (APDI2) in the precursor solution to change the zeta potential of the pristine colloids, the total interaction potential energy between colloidal particles with APDI2 could be controllably reduced, resulting in a higher coagulation probability and a lower critical nuclei concentration. In situ laser light scattering measurements confirmed the increased nucleation rate of the THP colloids with APDI2. The resulting film with APDI2 shows a pinhole-free morphology with fewer defects, achieving an impressive efficiency of 15.13 %.

Acetic acid-driven synthesis of environmentally stable MAPb0.5Sn0.5Br3 nano-assembly for anti-counterfeiting

In mixed Sn-Pb perovskites, the synergistic properties of tin (Sn) and lead (Pb) are leveraged, effectively combining the merits of Pb-based perovskites while simultaneously reducing Pb-associated toxicity. However, the propensity for Sn to undergo facile oxidation from Sn2+ to Sn4+ poses a significant challenge to the stability of these mixed perovskites, limiting their advancement. This study proposes an innovative acetic acid (HAc)-driven synthesis approach to obtain a stable chain-like MAPb0.5Sn0.5Br3 nano-assembly. Leveraging the acidic properties of HAc serves a dual purpose. Primarily, it curtails the oxidation of Sn2+ to Sn4+. Secondly, it orchestrates nanocrystals (NCs) into a more uniform and ordered chain-like assembly, a consequence of hydrogen bonding and coordination interactions facilitated by the HAc. Additionally, HAc demonstrates its capability to passivate MAPb0.5Sn0.5Br3 surface through coordination bonding with unsaturated sites (i.e., Sn2+ or Pb2+), thus effectively compensating for bromide vacancies. Introducing HAc during the synthesis process yields perovskite NCs with enhanced thermal resilience, optical and water stability. Drawing upon the different stimulus responses of synthesized perovskite NCs when exposed to external environment, the optical anti-counterfeiting labels are prepared. The findings provide a potent strategy for augmenting the stability of perovskite NCs, suggesting their potential applicability in anti-counterfeiting endeavors.

Oxidation-enabled SnS conversion to two-dimensional porous SnO2 flakes towards NO2 gas sensing

Tin dioxide (SnO2)-based electronic materials and gas sensors have attracted extensive attention from academia and industry. Herein we report the preparation of two-dimensional (2D) porous SnO2 flakes by thermal oxidation of 2D SnS flakes that serve as a self-sacrificial template. An oxidation-enabled, temperature-dependent matter conversion from SnS through three-phase SnS-SnS2-SnO2 (400 °C) and two-phase SnS2-SnO2 (600 °C) to pure-phase SnO2 (≥800 °C) is disclosed by means of combined XRD, TG-DSC and XPS studies. Meanwhile, the associated chemical reactions and the mass and heat changes during this solid-state conversion process are clarified. The as-prepared 2D SnO2 flakes exhibit structural porosity with tunable pore sizes and crystallite sizes/crystallinity, resulting in superior potential for NO2 sensing. At the optimized operating temperature of 200 °C, the prototype gas sensors made of porous SnO2 flakes show competitive sensing parameters in a broad NO2 concentration range of 50 ppb-10 ppm in terms of high response, faster response/recovery speeds, and good selectivity and stability. A sensing mechanism involving the adsorption and desorption of NO2/O2 molecules and the possible surface reactions is further rationalized for the SnO2 NO2 gas sensors.

Synergistic Optimization of Buried Interface by Multifunctional Organic-Inorganic Complexes for Highly Efficient Planar Perovskite Solar Cells

For the further improvement of the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs), the buried interface between the perovskite and the electron transport layer is crucial. However, it is challenging to effectively optimize this interface as it is buried beneath the perovskite film. Herein, we have designed and synthesized a series of multifunctional organic-inorganic (OI) complexes as buried interfacial material to promote electron extraction, as well as the crystal growth of the perovskite. The OI complex with BF4- group not only eliminates oxygen vacancies on the SnO2 surface but also balances energy level alignment between SnO2 and perovskite, providing a favorable environment for charge carrier extraction. Moreover, OI complex with amine (- NH2) functional group can regulate the crystallization of the perovskite film via interaction with PbI2, resulting in highly crystallized perovskite film with large grains and low defect density. Consequently, with rational molecular design, the PSCs with optimal OI complex buried interface layer which contains both BF4- and -NH2 functional groups yield a champion device efficiency of 23.69%. More importantly, the resulting unencapsulated device performs excellent ambient stability, maintaining over 90% of its initial efficiency after 2000 h storage, and excellent light stability of 91.5% remaining PCE in the maximum power point tracking measurement (under continuous 100 mW cm-2 light illumination in N2 atmosphere) after 500 h.