Guanidinium Iodide Research Articles

Multi‐Functional Interface Passivation via Guanidinium Iodide Enables Efficient Perovskite Solar Cells

AbstractPerovskite solar cells have become a leading contender in next‐generation photovoltaic technologies due to their high efficiency and low‐cost potential. Managing the deep defects present effectively in the crystal lattice and at the interfaces is essential for enhancing the performance and longevity of perovskite solar cells. Here, perovskite's crystallization modulation and interfacial defect passivation are achieved by developing a guanidinium iodide (GAI)‐based surface passivation strategy. The integration of GAI passivates the grain boundaries, leading to a perovskite thin film with a smoother and more uniform grain distribution, facilitating charge carrier transport. Notably, the ammonium group, unsaturated nitrogen atoms, and iodide ions in GAI can collectively repair the surface defects of perovskite through various pathways, effectively suppressing non‐radiative recombination, thereby enhancing the photovoltaic performance of the device. Ultimately, the champion device treated with GAI achieves a power conversion efficiency (PCE) of 23.02% and demonstrates similar ambient stability under unencapsulated conditions. These findings underscore the effectiveness of GAI passivation as a strategy to balance the improvement of the performance and stability of perovskite solar cells.

Improving perovskite solar cell efficiency and prolonging durability via interface modification with guanidinium iodide by post treatment method

The performance of perovskite solar cells (PSCs) can be significantly compromised by the presence of halide vacancies on the perovskite surface, leading to defects and a decline in stability and efficiency. Effectively addressing this challenge, the application of Guanidinium iodide (GAI) as a post dopant treatment (POST) has demonstrated success. GAI (POST) not only reduces surface defects but also minimizes halide deficiencies and mitigates losses due to interfacial charge recombination. When incorporating a GAI additive at a solution concentration of 1.5 mg/ml in the modification layer with the perovskite composition Cs0.1FA0.8MA0.1PbI3, the PSC showed a notable power conversion efficiency (PCE) of 20.7%, surpassing the 16.3% efficiency of the control device. Moreover, the adapted device demonstrated an impressive fill factor (FF) of 80.1%. Notably, the enhanced film of the modified device maintained over 80% of its initial efficiency for more than 312 h, highlighting the prospect of creating affordable, effective, and durable PSCs.

Effects of guanidinium iodide surface treatment on CH3NH3PbI3 perovskite solar cells with added decaphenylcyclopentasilane

The effects of guanidinium iodide surface treatment (GST) on CH3NH3PbI3 perovskite solar cells with decaphenylcyclopentasilane (DPPS) were investigated. GST decreases the carrier trap density and improves the photovoltaic characteristics. The X-ray diffraction results showed that the lattice constants of the perovskite crystals were increased by the insertion of GST and guanidinium into the methylammonium defects. The thermal stability of the unlaminated devices was tested in the air at 85 °C. The device prepared using GST exhibited the highest conversion efficiency. First-principles calculations supported these experimental results.

Guanidinium iodide salts as single component catalysts for CO2 to epoxide fixation

In this study, we present the synthesis, characterization and catalytic reactions of a new family of one-component catalysts based on guanidinium salts.

High Performance Hybrid‐Phototransistor Based on ZnON/perovskite Heterostructure Through Multi‐Functional Passivation

AbstractOrganic–inorganic halide perovskites are widely investigated for various optoelectronics devices such as photodetectors and solar cells. However, Pb‐based perovskite photodetectors perform poorly because of insufficient mobility and absence of an effective photoconductive gain mechanism. Herein, ZnON/perovskite heterostructures are demonstrated to realize the fabrication of high‐performance hybrid phototransistors. Additionally, a guanidinium iodide (GuI), alternating‐cation‐interlayer (ACI)‐type organic spacers, are utilized as an interface passivation layer. It is shown that the GuI interface layer reduces the defect density of the ZnON surface as well as the bulk perovskite film and promotes the separation and transport of photo‐generated charge carriers. Devices fabricated with the GuI interface passivation layer have a response speed of 0.1 s, excellent responsivity of 5.97 × 106 A W−1, and ultra‐high specific detectivity of 1.28 × 1018 Jones, the highest value among previously reported perovskite‐based hybrid phototransistors. This work provides valuable insights into the design and fabrication of high‐performance metal oxide/perovskite heterostructures with promising applications in future optoelectronic devices.

Buried interface modified by guanidinium iodide for enhanced efficiency and stability of perovskite solar cells

A guanidinium iodide layer is deposited on SnO2 to modify the buried interface of SnO2/CH3NH3PbI3 in perovskite solar cells. It is found that hydrogen bonds are formed between GAI and SnO2, which not only reduce the defects of SnO2 but also anchor the GAI molecules on the surface of SnO2 and then functioned as nucleation sites to form a 2D perovskite layer at the SnO2/CH3NH3PbI3 interface. Moreover, GAI molecules are demonstrated to distribute at the grain boundaries in the whole perovskite film, and hydrogen bonds are formed between GAI and perovskite. These hydrogen bonds effectively suppress the charge trapping and recombination regions induced by the under-coordinated iodine species. A CH3NH3Cl additive is found to be essential in the perovskite precursor, which manipulates the crystal growth dynamic and the vertical crystallization and hence the improved morphology of the perovskite films. Dramatically increased efficiency and stability are demonstrated in the perovskite solar cells. The optimized device shows a more than 20% higher PCE than the reference device. Besides, the device also remains 80% of its initial efficiency after storage for 60 days, suggesting the robust of this device.

Guanidium iodide treatment of size-controlled CsPbI3 quantum dots for stable crystal phase and highly efficient red LEDs

The optoelectronic properties of lead-halide perovskite quantum dots (QDs) can be tuned according to their halogen composition ratio and quantum size effect. However, the pure red emission of CsPbI3 QDs exhibits poor phase stability, thereby resulting in a phase transition to a nonphotoactive yellow phase at room temperature. These phase instabilities are accompanied by crystal strain and instability of the QD surface, which induce ion diffusion and desorption. Herein, we demonstrate the precise size control and postsynthetic guanidinium iodide (GAI) treatment to stabilize the crystal phase of CsPbI3 QDs. These synergistic effect results in higher ambient photoluminescence stability and photostability than those of pristine QDs. More importantly, the CsPbI3 QD light-emitting diodes achieve excellent external quantum efficiency of 22.5% and longer operational stability of over 10 h by the synergy effect of QD size control and GAI treatment.

Controlled crystallization and surface engineering of mixed-halide γ-CsPbI2Br inorganic perovskites via guanidinium iodide additive in air-processed perovskite solar cells

In this report, we demonstrate enlarged grain size (up to ∼3 μm) in ambient-stable black γ-phase CsPbI2Br thin films through the regulated addition of guanidinium iodide (GAI) as an effective volatile additive. Nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) measurements indicate the complete sublimation of GAI following annealing, with no inclusion inside the final γ-CsPbI2Br perovskite lattice. GAI is found to participate by retarding the cation–anion reaction via the Cs+ and GA+ cation-exchange process. We find that inorganic perovskite solar cells (IPSCs) devices made from (CsPbI2Br)0.925 + 0.075 GAI and a phenyltrimethylammonium chloride (PTACl) passivation retain a solar-friendly band-gap of 1.91 eV and excellent device performance, with the best open-circuit voltage reaching as high as 1.34 V, with highly reproducible and stable photo conversion efficiencies of 16.88% (for 0.09 cm2) and 15.60% (large area 1 cm2) under ambient conditions. Photostability analysis further demonstrated negligible efficiency loss over 1000 h under continuous one-sun equivalent illumination, indicating GAI additive as a promising approach toward ambient stable, all-inorganic high-efficiency solar cells.

Compositional engineering and surface passivation for carbon-based perovskite solar cells with superior thermal and moisture stability

The inherent stability of perovskite absorbers towards environmental factors is a major limitation towards commercializing perovskite solar cells (PSCs). In this regard, MaPbI3 (MAPI) is engineered to attain thermal stability by incorporating Guanidinium iodide (GuI) and moisture stability by surface passivation using 5- amino valeric acid iodide (5-AVAI). The surface passivation of Gu modified MAPI, hereafter termed as GUMAPI, exhibits a 2D/3D perovskite interface, which, facilitates perovskite to attain high moisture and temperature stability. Various concentrations of 5-AVAI are used as the surface passivator. The stability of the surface-modified Gu doped MAPI films is studied thoroughly using time-dependent water contact angle measurements, in-situ temperature-dependent XRD analysis, and XRD studies of aged perovskite films under ambient conditions. 1AV films exhibit excellent temperature (>150 °C) and ambient stability (>59 days) when compared with control perovskite films (GUMAPI). The stability and performance of these perovskite films in a carbon-PSCs (CPSCs) architecture are evaluated by studying the current-voltage characteristics and assessing the device performance at various intervals. The 1AV-based CPSCs exhibit performance surpassing the control (GUMAPI) devices. A 9.0% increment is observed in the 1AV-based CPSCs compared to the GUMAPI-based CPSCs with an efficiency of 13.2% and a T80 lifetime of 93.2% without encapsulation.

Structural and Photophysical Properties of Guanidinium–Iodide‐Treated Perovskite Solar Cells

Use of the guanidinium iodide (GAI) cation is widely recognized as an interface engineering technique for perovskite solar cells that deliver stability improvements via defect passivation on surfaces and grain boundaries. However, a comprehensive understanding of the relationship between the structural and photophysical properties is lacking. Herein, GAI‐induced perovskite structural modifications, including derivative phases and underlying transitions, are detected in GAI surface‐treated Cs0.07MA0.14FA0.79Pb(I0.83Br0.17)3 through an analysis of X‐ray and electron diffraction and microscopy data. An optimum GAI solution concentration at 10 mg mL−1 can eliminate excess PbI2, improve crystallinity, and increase grain size of the as‐prepared perovskite films. However, a further increase to 20–40 mg mL−1 induces new (FAPbI3) x (GA2PbI4) x phases and a reduction in crystallinity and grain size. In addition, from confocal photoluminescence imaging, it is observed that 10 mg mL−1 GAI also helps to remove the microscale spatial heterogeneities, demonstrating optimum device performance. These results show that understanding the impact on structure and microstructure of the selection and concentration of surface treatment agents is critical for the homogenization of perovskite optoelectronic properties and achieving efficient device.

In-Depth Insight into the Effect of Hydrophilic-Hydrophobic Group Designing in Amidinium Salts for Perovskite Precursor Solution on Their Photovoltaic Performance.

Amidinium salts have been utilized in perovskite precursor solutions as additives to improve the quality of perovskite films. The design of hydrophilic or hydrophobic groups in amidinium salts is of great importance to photovoltaic device performance and stability in particular. Here we report a contrast study of a guanidinium iodide (GUI) additive with a hydrophilic NH2 group, and a N,1-diiodoformamidine (DIFA) additive with a hydrophobic C-I group, to investigate the group effect. The addition of GUI or DIFA was beneficial to achieve high quality perovskite film and superior photovoltaic device performance. Compared with GUI, the addition of the DIFA in a perovskite precursor solution enhanced the crystal quality, reduced the defect density, and protected the water penetration into perovskite film. The perovskite solar cell (PSC) devices showed the best power conversion efficiency (PCE) of 21.19% for those modified with DIFA, as compared to 18.85% for the control, and 20.85% for those modified with GUI. In benefit to the hydrophobic C-I group, the DIFA-modified perovskite films and PSC exhibited the best light stability, thermal stability, and humidity stability in comparison to the control films and GUI-modified films. Overall, the introduction of a hydrophobic group in the amidinium salts additive was demonstrated to be an efficient approach to achieve high quality and stable perovskite film and PSC devices.

Varied performance of printable mesoscopic perovskite solar cells by the non-stoichiometric precursor

Halide perovskite semiconductors such as MAPbI3 always fluctuate around their stoichiometric compositions due to the weighing or annealing, which causes performance variation of related devices. Here, we investigate the comprehensive impact of non-stoichiometric MAPbI3 precursor on the performance including power conversion efficiency (PCE), hysteresis, and stability of printable mesoscopic perovskite solar cells (p-MPSCs). Excess MAI improves PCE, suppresses hysteresis, and enhances stability by promoting hole transport and passivating defects evaluated by a designed mesoporous space-charge-limited-current device, while excess PbI2 impairs device performance. Replacing excess MAI with other monovalent cation halide salts including guanidinium iodide (GUAI), 2-phenylethylamine hydroiodide (PEAI) and rubidium iodide (RbI) further improves the device PCE to 17.02% and minimizes the hysteresis. Our work reveals that making monovalent cation halide salts such as MAI rather than PbI2 excessive is positive for the comprehensive performance enhancement of PSCs and developing more suitable salt substitution will benefit industrializing PSCs.

Surface Treatment of Inorganic CsPbI3 Nanocrystals with Guanidinium Iodide for Efficient Perovskite Light-Emitting Diodes with High Brightness

HighlightsA facile and effective surface passivation strategy was demonstrated to improve the optical and stability of CsPbI3 nanocrystals by using guanidinium iodide post-treatment.Guanidinium cations was shown to be compatible with CsPbI3 perovskite, leading to significantly improved surface properties of CsPbI3 nanocrystals.Performance of the CsPbI3 nanocrystal-based light-emitting device was enhanced by 3.6 folds.

Millimeter‐Sized Clusters of Triple Cation Perovskite Enables Highly Efficient and Reproducible Roll‐to‐Roll Fabricated Inverted Perovskite Solar Cells

AbstractThe high‐power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) on lab‐scale devices trigger the need to develop scalable manufacturing processes to accelerate their commercialization transition. A roll‐to‐roll (R2R) vacuum‐free printing on flexible substrates allows for high‐volume and low‐cost manufacturing which is especially well‐suited for PSCs due to its solution processibility and low‐temperature annealing requirements. Herein, a facile hot deposition technique is reported to fabricate triple‐cation (Cs0.07FA0.79MA0.14Pb(I0.83Br0.17)3) perovskite films in an ambient environment using a R2R slot‐die coating method. This perovskite composition, whilst being most studied in lab devices due to its high efficiency and stability, has not been applied in R2R fabrication thus far. The demonstrated R2R slot‐die coated flexible PSCs achieve stabilized PCE reaching 12% at maximum power point in inverted “p‐i‐n” architectures, the highest efficiency reported to date for R2R inverted PSCs. To achieve this, the underlying hole transport layer (poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate) is modified with guanidinium iodide additive which leads to the formation of large millimeter‐sized perovskite clusters, improved perovskite crystallinity, and enhanced charge‐transfer efficiency. This study highlights the potential of the facile hot‐deposition method while providing critical insights into the role of interfacial engineering in eliminating performance losses and fabricating efficient printed flexible PSCs.

Double Side Interfacial Optimization for Low‐Temperature Stable CsPbI2Br Perovskite Solar Cells with High Efficiency Beyond 16%

CsPbI2Br perovskite solar cells have achieved rapid development owing to their exceptional optoelectronic properties and relatively outstanding stability. However, open‐circuit voltage (Voc) loss caused by band mismatch and charge recombination between perovskite and charge transporting layer is one of the crucial obstacles to further improve the device performance. Here, we proposed a bilayer electron transport layer ZnO(bottom)/SnO2(top) to reduce the Voc loss (Eloss) and promote device Voc by ZnO insert layer thickness modulation, which could improve the efficiency of charge carrier extraction/transfer and suppress the charge carrier recombination. In addition, guanidinium iodide top surface treatment is used to further reduce the trap density, stabilize the perovskite film and align the energy levels, which promotes the fill factor, short‐circuit current density (Jsc), and stability of the device. As a result, the champion cell of double‐side optimized CsPbI2Br perovskite solar cells exhibits an extraordinary efficiency of 16.25% with the best Voc as high as 1.27 V and excellent thermal and storage stability.

Improving the Performance of Perovskite Solar Cells via a Novel Additive of N,1‐Fluoroformamidinium Iodide with Electron‐Withdrawing Fluorine Group

AbstractAdditives are widely adopted for efficient perovskite solar cells (PSCs), and proper additive design contributes a lot to PSCs’ various breakthroughs. Herein, a novel additive of N,1‐fluoroformamidinium iodide (F‐FAI), whose cation replaces one amino group in guanidinium (GA+) with electron‐withdrawing fluorine group, is synthesized and applied as the additive for PSCs. The electron‐withdrawing effect of fluorine promotes the molecular polarity of N,1‐fluoroformamidine (F‐FA), enhancing the interaction of N,1‐fluoroformamidinium (F‐FA+) with MAPbI3. Compared with the nonpolar GA+, F‐FA+ improves the crystallinity, passivates the defect, and downshifts the Fermi level of MAPbI3 more significantly. The charge transfer and built‐in field in printable triple mesoscopic PSCs are therefore enhanced. Moreover, charge transport in MAPbI3 is also promoted by F‐FAI. With these benefits, a power conversion efficiency of 17.01% for printable triple mesoscopic PSCs with improved open‐circuit voltage and fill factor is obtained with the addition of F‐FAI, superior to the efficiency of 15.24% for those devices with guanidinium iodide additives.

Grain Boundary Defect Passivation in Quadruple Cation Wide‐Bandgap Perovskite Solar Cells

Development of high‐performance wide‐bandgap perovskites is a key component to enable tandem solar cells with either a silicon or low‐bandgap perovskites. However, the presence of defects in the Br‐rich wide‐bandgap perovskites, especially in the grain boundaries (GBs) has been particularly challenging and limits its performance. Herein, to accomplish the passivation of these defects, a combination of cation management with rubidium (Rb) introduction into the triple cation combination of cesium/formamidinium/methylammonium (CsFAMA) is exercised. Passivation is further enhanced by secondary growth (SG) using guanidinium iodide. In‐depth assessments of GB defect passivation are performed using Kelvin probe force microscopy (KPFM) and nanoscale charge‐carrier dynamics mappings provide insightful details on the presence of GBs defects and their suppression by the cation management and SG techniques. Reduction of unreacted PbX2 to realize a highly crystalline perovskite surface is achieved after incorporating Rb and SG treatment. As a result, a champion cell for 1.78 eV (FA0.79MA0.16Cs0.05)0.95Rb0.05Pb(I0.6Br0.4)3 wide‐bandgap perovskite with an efficiency of 17.71% along with enhancement in all photovoltaic parameters is achieved. This study introduces a new way to analyze GB defects and reveals the consequence of defect passivation on charge‐carrier dynamics for realizing efficient perovskites.

Passivation of triple cation perovskites using guanidinium iodide in inverted solar cells for improved open-circuit voltage and stability

Inverted device architectures in perovskite research were promising for faster commercialization given the simple processing routes and choice of hole transport materials such as PEDOT:PSS.

Surface Treatment of Perovskite Layer with Guanidinium Iodide Leads to Enhanced Moisture Stability and Improved Efficiency of Perovskite Solar Cells

AbstractInterfacial engineering between the perovskite and hole transport layers has emerged as an effective way to improve perovskite solar cell (PSC) performance. A variety of organic halide salts are developed to passivate the traps and enhance the charge carrier transport. Here, the use of guanidinium iodide (GuaI) for interfacial modification of mixed‐cation (Cs)x(FA)1−xPbI3 perovskite films, which results in the formation of a low‐dimensional δ‐FAPbI3‐like phase on the 3D perovskite surface, is reported. The presence of this thin layer facilitates charge transfer at interfaces and reduces charge carrier recombination pathways as evidenced by enhanced carrier lifetimes and favorable interfacial band alignment. As a result, the power conversion efficiency of the control device is boosted from 19.22% to 20.07%, mainly due to improved open‐circuit voltage (Voc) and fill factor. Furthermore, the post‐treatment with GuaI improves the moisture stability of perovskite polycrystalline films and ambient stability of PSCs.

Reconfiguration of Interfacial and Bulk Energy Band Structure for High‐Performance Organic and Thermal–Stability Enhanced Perovskite Solar Cells

Tin oxide (SnO2) offers its advantages in widespread applications that require efficient carrier transport. However, the usages of SnO2in organic solar cells are hindered because of dangling bonds on the surface of SnO2. Herein, PFN‐Br as an interfacial layer to tailor the work function of SnO2is adopted, making it an ideal candidate for interfacial material in organic electronics. Meanwhile, such an efficient SnO2/PFN‐Br electron transport layer (ETL) can also be applied to perovskite devices and achieve competitive efficiency. To eliminate current–voltage hysteresis and improve poor thermodynamic stability of perovskite solar cells (PSCs), 5 mol% of guanidinium iodide (GAI) into the (MA)x(FA)1 − xPbI3precursor solution is incorporated, enabling the formation of triple‐cation perovskite films with excellent optoelectronic quality and stability. The combination of an SnO2/PFN‐Br ETL and GAI doping strategy finally delivers power conversion efficiencies over 21% and negligible current–voltage hysteresis in planar PSCs. These improvements arise from the strong hydrogen bonding caused by the incorporation of GA+. It can stiffen the inorganic Pb–I lattice of the unit cell and restrain the formation of iodine vacancies defects. Moreover, the strong hydrogen bonding can immobilize iodide ion and thus enhance the thermal stability of the corresponding device.