Sn Perovskite Research Articles

Dual-site passivation of tin-related defects enabling efficient lead-free tin perovskite solar cells

Tin (Sn) perovskites as photovoltaic materials show great promise due to their suitable bandgaps and lower toxicity. However, various defects in Sn perovskites induce significant losses in devices. In this work, we report a strategy of dual-site passivation of Sn-related defects in lead-free Sn perovskite solar cells. We adopt ethylenediammonium halide salts (i.e., EDAI2 and EDABr2) as additives in Sn perovskite and find that both EDAI2 and EDABr2 can suppress Sn oxidation and passivate trap states, however, EDABr2 works better than EDAI2 in terms of passivating undesired grain boundaries and surface Sn vacancies, and reducing background hole density, due to the synergistic roles of EDA2+ cation and Br- anion. Moreover, EDABr2 exhibits more consummate passivation effect on SnI antisite defects as deep-level traps due to its larger electrostatic potential and shorter bonding length between -Br and -Sn. These enable great suppression of non-radiative recombination and enhancement of charge carrier transport. As a result, the best-performing EDABr2-modified device achieves a power conversion efficiency of 14.23% with long-term durability of keeping ∼93% of its initial efficiency after storing for ∼4000 h and improved operational stability. Our work provides a promising approach to choose satisfactory passivators and fabricate efficient Sn perovskite solar cells.

Prevention of Noise Current Generation in Tin‐Based Lead‐Free Perovskites for Highly Sensitive Photodetection

AbstractLead (Pb) halide perovskites have attracted significant attention in the field of optoelectronics. However, due to the disadvantages associated with the presence of Pb in perovskite, its use should be minimized, if not completely eliminated. Herein, an efficient Pb‐free Sn‐based halide perovskite photodetector (PD) that is sensitive to visible and near‐infrared light is developed. The Sn perovskite is characterized with low toxicity and a narrow bandgap, and exhibits lower shunt leakage and a higher built‐in potential compared with a Pb‐based perovskite. Also, the relatively stronger bond strength between Sn and iodine ions in comparison with that observed in the Pb‐based perovskite effectively prevents charge injections that are vulnerable to dark current suppression. The Sn‐based perovskite PD demonstrates a high signal‐to‐noise ratio (SNR) of 51.12 dB, as well as an excellent cut‐off frequency of 763 kHz. To the best knowledge, this device is one of the fastest and most efficient photodiode‐type Sn‐based perovskite PDs developed to date. Unlike the Pb‐based perovskite device, the Sn‐based perovskite PD retains its high SNR over time. This effect may be attributed to the low movement of ion vacancies and degree of vertical shunt leakage in the perovskite material.

Ultrathin Self-Assembly Two-Dimensional Metal–Organic Framework Films as Hole Transport Layers in Ideal-Bandgap Perovskite Solar Cells

Two-dimensional conjugated metal–organic framework (2D c-MOF) Cu3(HHTT)2 (2,3,7,8,12,13-hexahydroxytetraazanaphthotetraphene, HHTT) is found to be an ideal hole transport material for Pb–Sn perovskite solar cells (PSCs) for the first time. 2D c-MOF films are conveniently prepared by a self-assembly deposition method and used in ideal-bandgap Pb–Sn mixed PSCs. The ultrasmooth surface of the Cu3(HHTT)2 film can facilitate perovskite growth and enable defect passivation on the perovskite surface. The self-assembly approach is suitable for preparing large-area films conformally on a substrate, promising the application of the film in large-area devices. Encouragingly, an efficiency over 22% is obtained from ideal-bandgap PSCs. Moreover, an efficiency of 19.86% for large-area ideal-bandgap PSCs is achieved from devices with an area of 1 cm2. This work demonstrates that 2D c-MOFs are promising charge transport materials for high-efficiency and large-area PSCs.

Multidentate Chelation Heals Structural Imperfections for Minimized Recombination Loss in Lead‐Free Perovskite Solar Cells

AbstractTin‐based perovskite solar cells (Sn‐PSCs) have emerged as promising environmentally viable photovoltaic technologies, but still suffer from severe non‐radiative recombination loss due to the presence of abundant deep‐level defects in the perovskite film and under‐optimized carrier dynamics throughout the device. Herein, we healed the structural imperfections of Sn perovskites in an “inside‐out” manner by incorporating a new class of biocompatible chelating agent with multidentate claws, namely, 2‐Guanidinoacetic acid (GAA), which passivated a variety of deep‐level Sn‐related and I‐related defects, cooperatively reinforced the passivation efficacy, released the lattice strain, improved the structural toughness, and promoted the carrier transport of Sn perovskites. Encouragingly, an efficiency of 13.7 % with a small voltage deficit of ≈0.47 V has been achieved for the GAA‐modified Sn‐PSCs. GAA modification also extended the lifespan of Sn‐PSCs over 1200 hours.

Multidentate Chelation Heals Structural Imperfections for Minimized Recombination Loss in Lead-Free Perovskite Solar Cells.

Tin-based perovskite solar cells (Sn-PSCs) have emerged as promising environmentally viable photovoltaic technologies, but still suffer from severe non-radiative recombination loss due to the presence of abundant deep-level defects in the perovskite film and under-optimized carrier dynamics throughout the device. Herein, we healed the structural imperfections of Sn perovskites in an "inside-out" manner by incorporating a new class of biocompatible chelating agent with multidentate claws, namely, 2-Guanidinoacetic acid (GAA), which passivated a variety of deep-level Sn-related and I-related defects, cooperatively reinforced the passivation efficacy, released the lattice strain, improved the structural toughness, and promoted the carrier transport of Sn perovskites. Encouragingly, an efficiency of 13.7 % with a small voltage deficit of ≈0.47 V has been achieved for the GAA-modified Sn-PSCs. GAA modification also extended the lifespan of Sn-PSCs over 1200 hours.

Phenylethylammonium-formamidinium-methylammonium quasi-2D/3D tin wide-bandgap perovskite solar cell with improved efficiency and stability

Wide bandgap (WBG) Sn perovskite solar cells (PSCs) efficiency enhancement is another sought after field and to resolve the issues related to fast crystallization, trap density and moisture induced oxidation of Sn2+ state in Sn perovskite, we endeavor the benefits of substituting hydrophobic phenylethlammonium (PEA+) cation into WBG PEAxFA0.75MA0.25-xSnI2Br through compositional engineering. We have realized that PEA+ substitution in WBG Sn perovskite led to form 2D/3D mixed perovskite and execute preferential orientation of 3D perovskite planes with controlled crystallinity. Our observation suggests that 2D perovskite phase here helps in merging the grain boundaries and reduce the rate of moisture penetration which ultimately controlled further oxidation of Sn2+. Also, the substitution of PEA+ in WBG Sn perovskite helps in modulating the band energies and aids to efficient electron injection from perovskite to transport layer. Compared to the 3D counterpart, 2D/3D perovskite exhibits slow lifetime decay (τavg = 1.25 ns), suppressed trap state density (1.7 × 1016 cm−3), improved band alignment with slower carrier recombination (τ = 1217 μs) and efficient charge extraction. As compared to FASnI2Br (PCE of 2.38%) and FA0.75MA0.25SnI2Br (PCE of 3.66%), our champion device PCE of 7.96% (Certified PCE of 7.84%) with Jsc of 16.89 mA·cm−2, Voc of 0.67 V and FF of 70.36% was achieved for PEA0.15FA0.75MA0.10SnI2Br, which is the highest PCE till date with compositional engineering strategy. The device kept under N2 atmosphere retained nearly original PCE after almost 1500 hrs and air stability of 300 hrs without encapsulation, indicating excellent stability.

Structural, elastic, electronic and optical properties of lead free ZnMO3 (M = Ge, Sn) perovskites from first principles investigation

The structural, elastic, mechanical, electronic and optical properties of lead free noncentrosymmetric ZnMO3 (M = Ge, Sn) have been studied using density functional theory based simulation methods. The optimized lattice parameters were compared with reported experimental and theoretical values and were found good agreement. The compounds are mechanically stable satisfying the Born criteria of single crystal elastic constants. Some important mechanical properties were investigated from calculated single crystal elastic constants. Young's moduli were found to be 262.30 GPa for ZnGeO3 and 179.70 GPa for ZnSnO3. Electronic band structure together with total and orbital resolved Density of States (DOS) have been revisited which reveal that, both are direct band gap semiconductors and should be potential materials for optoelectronic applications. The optical properties have been studied in detail.

Alkyl Diamine-Induced (100)-Preferred Crystal Orientation for Efficient Pb–Sn Perovskite Solar Cells

The narrow band gap lead–tin (Pb–Sn) perovskite is a promising light absorption layer for highly efficient perovskite solar cells (PSCs), particularly for tandem applications. However, its random crystal orientation dramatically limits its power conversion efficiency (PCE). Here, a propane diamine bromide (PDABr) additive is developed to effectively modulate the Pb–Sn perovskite to grow along the (100)-preferred orientation. It is found that the PDA cations naturally anchor onto the colloidal perovskite nucleus to serve as a surface template to modulate the perovskite crystal to grow preferentially along its (100) orientation, while the bromide ions aid in increasing the grain size, resulting in a densely packed film with significantly reduced density of grain boundaries. As a result, the PDABr-based film exhibits increased carrier mobility and reduced defect density. With these merits, the PDABr-based Pb–Sn PSCs demonstrated an impressive PCE of 20.41%, which is much higher than that of the control device (16.23%). This work provides a general approach to realize the preferred crystal growth for Pb–Sn perovskite films to attain high optoelectronic performance.

Suppressing the formation of tin vacancy yields efficient lead-free perovskite solar cells

Tin hybrid perovskite solar cells (TPSCs) have emerged as the most promising candidate to the lead counterparts for the low toxicity and high theoretical efficiency. However, the easy Sn2+ oxidation and related defects hinder further efficiency and stability improvement. Therefore, a facile Lewis base molecule of 4-amino-3-hydroxybenzoic acid (4A3HA) is employed in the perovskite precursor to coordinate with the under-coordinated Sn2+ ions and passivate the Sn defects. The effective suppression of the formation of Sn vacancy also has been verified from the density functional theory calculations. The 4A3HA modification significantly suppresses the trap-mediated recombination of Sn perovskite film. Accordingly, these benefits deliver a high power conversion efficiency (PCE) of 13.43% for TPSCs with notably improved on-shelf and thermal stability.

Using Ligand Engineering to Produce Efficient and Stable Pb-Sn Perovskite Solar Cells with Antioxidative 2D Capping Layers.

Pb-Sn binary halide perovskites are a promising photovoltaic material due to their low toxicity and optical absorption spectrum well matched to the solar spectrum. However, the ready oxidation of Sn2+ to Sn4+ makes the material system currently too unstable to commercialize. Herein, ligand engineering based on antioxidative tyramine (hydrochloride, TACl) is presented for the first time to increase the stability of this material system. Using this strategy, we generate a two-dimensional (2D) capping layer on top of a standard three-dimensional Pb-Sn film. After capping, the surface defects can be passivated and the TACl-based 2D perovskite effectively protected Sn2+ from oxidation, which stabilized the Sn-Pb perovskite composition, avoiding the Pb-based perovskite formation. It is further found that the TACl treatment suppressed the halide segregation and improved the perovskite film photostability. Cell efficiency increases from 16.25 to 18.28% and device lifetime (T80) increases from less than 100 to over 1000 h. Our finding suggests that tuning ligand form/function represents a potentially highly productive direction to explore when trying to produce stable tin-based perovskite devices.

A radically different path to high-performance Sn perovskite solar cells

A radically different path to high-performance Sn perovskite solar cells

High performance wide bandgap Lead-free perovskite solar cells by monolayer engineering

2PACz monolayer on PEDOT-PSS as the hole transport layer (HTL) was introduced to the inverted p-i-n Tin (Sn) based perovskite solar cells (PSCs) with 1.62 eV bandgap (Wide bandgap). 2PACz giving high efficiency to Pb perovskite solar cells was not effective at all for the Sn perovskite solar cells. We found that the efficiency was enhanced by synergistic effects of the 2PACz monolayer and PEDPT-PSS. The efficiency enhancement was explained by the compactness of the perovskite layer fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, an energetically aligned interface of the HTL/Sn-based perovskite absorber, the lower lattice disordering and reduced non-radiative recombination of the perovskite layer. The cell stability was improved by the compact surface morphology of the Sn perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS and the suppression of direct contact between PEDOT-PSS and perovskite film. EDA0.01(GA0.06(FA0.8Cs0.2)0.94)0.98SnI2Br perovskite fabricated on bilayer consisting of 2PACz monolayer on PEDOT-PSS, gave the power conversion efficiency (PCE) of 8.66%, which is the highest performance for wide bandgap Sn perovskite solar cells reported so far.

Large synergy effects of doping, a site substitution, and surface passivation in wide bandgap Pb-free ASnI2Br perovskite solar cells on efficiency and stability enhancement

Tin (Sn) based perovskite solar cells (PSCs) are rapidly getting attention due to their relatively less toxic nature compared to lead-PSCs. However, Sn perovskites previously reported are narrow-bandgap materials. Wide-bandgap perovskites, which are the key materials for the top layer of lead-free tandem solar cells, are rarely researched up to now. Here, it is demonstrated that optoelectronic properties of the GA0.06(FA0.8Cs0.2)0.94SnI2Br based wide-bandgap perovskite can be improved by exploring (1) Germanium (II) Iodide (GeI2) doping, (2) incorporation of Ethylenediamine Bromide (EDABr2) at A site, (3) EDA passivation. The incorporation of big organic cation EDABr2 in the wide-bandgap tin perovskite crystal structure together with GeI2 doping made the carrier lifetime of perovskite absorber increase from 1.1 ns to 22.8 ns and the power conversion efficiency (PCE) was enhanced from 2.55% to 4.86% with an increment of Voc ˃ 100 mV. Further, we achieved the balanced charge transfer by using EDA passivation on the optimized perovskite surface film. As a result, the efficiency was improved from 4.86% to 7.50%, which is the highest efficiency among lead-free wide bandgap PSCs. This enhanced photovoltaic performance of the wide-bandgap tin perovskite device presents a wide application in lead-free tandem towards commercial development.

Ultrasensitive Near-Infrared Circularly Polarized Light Detection Using 3D Perovskite Embedded with Chiral Plasmonic Nanoparticles.

Chiral organic ligand‐incorporated low‐dimensional metal‐halide perovskites have received increasing attention for next‐generation photodetectors because of the direct detection capability of circularly polarized light (CPL), which overcomes the requirement for subsidiary optical components in conventional CPL photodetectors. However, most chiral perovskites have been based on low‐dimensional structures that confine chiroptical responses to the ultraviolet (UV) or short‐wavelength visible region and limit photocurrent due to their wide bandgap and poor charge transport. Here, chiroptical properties of 3D Cs0.05FA0.5MA0.45Pb0.5Sn0.5I3 polycrystalline films are achieved by incorporating chiral plasmonic gold nanoparticles (AuNPs) into the mixed Pb—Sn perovskite, without sacrificing its original optoelectronic properties. CPL detectors fabricated using chiral AuNP‐embedded perovskite films can operate without external power input; they exhibit remarkable chirality in the near‐infrared (NIR) region with a high anisotropy factor of responsivity (g res) of 0.55, via giant plasmon resonance shift of chiral plasmonic AuNPs. In addition, a CPL detector array fabricated on a plastic substrate demonstrates highly sensitive self‐powered NIR detection with superior flexibility and durability.

Influence of intrinsic defects on the structure and dynamics of the mixed Pb–Sn perovskite: first-principles DFT and NAMD simulations

The mixed tin (Sn) and lead (Pb) perovskite compositions have shown great potential in perovskite photovoltaic devices due to the significantly enhanced material stability and prolonged carrier lifetime, compared to the pure Sn halide perovskites.

Highly Efficient Hole Transport Layer‐Free Low Bandgap Mixed Pb–Sn Perovskite Solar Cells Enabled by a Binary Additive System

AbstractThe development of high‐performance hole transport layer (HTL)‐free perovskite solar cells (PSCs) with a simplified device structure has been a major goal in the commercialization of PSCs due to the economic advantage of low manufacturing cost. Unfortunately, low bandgap (Eg) mixed Pb–Sn perovskites, which have promising utility for constructing efficient all‐perovskite tandem solar cells, have rarely been explored in simplified HTL‐free device configurations. In this study, efficient band bending and defect engineering at the interface between perovskite and indium tin oxide (ITO) are realized via a binary additive system using copper thiocyanate (CuSCN) and glycine hydrochloride (GlyHCl). Using mixed Pb–Sn perovskites decorated with crystalline p‐type CuSCN, the energy level alignment at the hole extractive interface is modulated in favor of hole extraction, simultaneously increasing hole mobility. Suppressed nonradiative carrier recombination in the perovskite bulk, or across the charge extractive interface, is further achieved by GlyHCl without disturbing the efficient hole transfer characteristics. Notably, a more optimized band alignment is achieved at the hole extractive interface with the addition of GlyHCl. The HTL‐free mixed Pb–Sn PSC shows an efficiency up to 20.1% under forward bias with negligible hysteresis, comparable to state‐of‐the‐art high‐performance full‐structured mixed Pb–Sn PSCs.

A DFT study of the stability and optoelectronic properties of all-inorganic lead-free halide perovskites

In recent years, all-inorganic lead-free CsGe0.5Sn0.5I3 has been proposed as a promising candidate for perovskite solar cells. In the present study, the stability and optoelectronic properties of the CsGeX3 and Cs2GeX6 (X = Cl, Br, I) compounds and mixed CsGe1-xSnxI3 perovskites have been explored using first-principles calculations. The results indicate that the CsGeX3 compounds and Cs2GeCl6 are stable at room temperature, while Cs2GeBr6 and Cs2GeI6 are unstable. A phase transition is revealed for the CsGe1-xSnxI3 systems when the ratio of Sn doping is over 0.53. In addition, both CsGe2/3Sn1/3I3 and CsGe0.25Sn0.75I3 show the potential tendency for phase segregation. CsGe2/3Sn1/3I3 and CsGe0.25Sn0.75I3 have suitable band gaps and exhibit strong absorption coefficients, which are the promising candidates for solar cells. Our work demonstrates the favorable optoelectronic properties of novel lead-free mixed Ge–Sn perovskites for single-junction solar cells.

Enhancing Performance and Stability of Tin Halide Perovskite Light Emitting Diodes via Coordination Engineering of Lewis Acid–Base Adducts

AbstractFor resolving toxicity issues of Pb‐based perovskites, Sn‐based perovskites have been widely studied as a promising alternative due to similar valence electron configuration between Sn2+ and Pb2+. However, desired Sn2+ in the precursor solution and film is easily oxidized to Sn4+, causing detrimental Sn vacancies and impurities in the films. Unfortunately, dimethyl sulfoxide, a ubiquitously used Lewis base for the fabrication of high‐quality perovskite thin films via the adduct approach, further accelerates the oxidation of Sn2+ in the precursor solution. Herein, N,N′‐dimethylpropyleneurea (DMPU) is proposed as an alternative Lewis base for the fabrication of high‐quality Sn‐based perovskite thin films. The strongly coordinating Lewis base DMPU is shown to suppress the oxidation of Sn2+ in the precursor solution while promoting growth of uniform and highly crystalline thin films. The PEA2SnI4 perovskite light emitting diode (PeLED) based on DMPU demonstrates dramatically improves luminance (L): a more than sixfold enhanced external quantum efficiency (EQE) and better operational stability than those of the device fabricated without DMPU. The optimum PeLED based on DMPU achieves a maximum L and EQE of 68.84 cd m−2 and 0.361%, respectively. This study provides an important methodological base for studying Sn perovskites for development of high‐performance and eco‐friendly PeLEDs.

Pyrene‐Based Small‐Molecular Hole Transport Layers for Efficient and Stable Narrow‐Bandgap Perovskite Solar Cells

Lead–tin (Pb–Sn) hybrid perovskite materials possess ideal narrow bandgaps (1.2–1.4 eV) for efficient single‐junction and tandem solar cells. Poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is commonly used as hole transport layer (HTL) for Pb–Sn perovskite solar cells (PSCs), despite its poor stability with these perovskites. Here, two new octacyclic heteroaromatic molecules, pyrenodiindole (PDI) and pyrenodi‐(7‐azaindole) (PDAI), are presented as the HTL for narrow‐bandgap (1.23 eV) p–i–n Pb‐Sn PSCs. The self‐assembled reciprocal hydrogen‐bonded solid‐state structure of PDAI bestows robustness compared to PDI, making it less vulnerable in processing the perovskite film on top, and improves the reproducibility of device fabrication. Transient photocurrent measurements and light‐intensity‐dependent device characteristics indicate that PDI and PDAI possess similar hole extraction properties to PEDOT:PSS. As a result, similar open‐circuit voltages and fill factors are obtained in the PSCs. Interestingly, the use of thin PDI and PDAI as HTL in PSCs changes the optical interference and reduces parasitic absorption in the near‐infrared region, resulting in an improved short‐circuit current density. Consequently, a higher power conversion efficiency of 16.1% is obtained for PDI and PDAI, compared to 15.1% for PEDOT:PSS. In addition, the self‐assembled structure of PDAI led to a notable enhancement of device stability.

Comparative Study of Recombination Dynamics in Optimized Composition of Sn- Versus Pb-Based Perovskite Solar Cells.

The energy band gaps of Pb halide perovskites are higher than the optimal band gap required for single-junction solar cells, governed by the Shockley-Queisser radiative limit. The pure Sn and Pb-Sn mixed-based perovskites have drawn significant attention due to their ability to lead to lower band gaps and open a new door for all perovskite tandem applications. There has been continuous progress toward the rapid improvement in the power conversion efficiency of Sn and Pb-Sn mixed-based perovskite solar cells (PSCs). Along with efforts for efficiency, it is worth analyzing the in-depth recombination dynamics for further development of Sn-based PSCs. The lower bimolecular recombination rate constant (k) is often attributed to the high performance of PSCs. Herein, we study the role of "B" cations in charge carrier recombination dynamics (CCRD) of ABX3 (A = MA+, FA+, and Cs+; B = Pb2+, Sn2+, and X = I-)-based PSCs. We fabricated p-i-n configuration-based FA0.95Cs0.05PbI3 (pure Pb), MA0.20FA0.75Cs0.05SnI3 (pure Sn), and (MAPbI3)0.4(FASnI3)0.6 (Pb-Sn mixed) PSCs and compared the CCRD of all the three PSCs. We optimized the Sn-based perovskite thin film (pure Sn) in terms of moisture and thermal stability in order to minimize the error due to perovskite degradation. We note that despite having lower open-circuit voltage (VOC), a pure Sn-based PSC shows lower k than that of Pb-Sn mixed and pure Pb-based PSCs, which is a contradictory result. This slow relaxation lifetime of the charge carrier in Sn-based PSCs can be correlated with recombination through the defect states without introducing the quasi-Fermi-level splitting. Furthermore, our results suggest that the rate law of charge carrier decay has nonlinear dependence of k on n in Sn-based PSCs, whereas it is linear in the other two cases.