Ultra-high open-circuit voltage of tin perovskite solar cells via an electron transporting layer design

Enhancing the Performance of 2D Tin-Based Pure Red Perovskite Light-Emitting Diodes through the Synergistic Effect of Natural Antioxidants and Cyclic Molecular Additives

Tin (Sn)-based perovskites are being investigated in many optoelectronic applications given their similar valence electron configuration to that of lead-based perovskites and the potential environmental hazards of lead-based perovskites. However, the formation of high-quality Sn-based perovskite films faces several challenges, mainly due to the easy oxidation of Sn2+ to Sn4+ and the fast crystallization rate. Here, to develop an environmentally friendly process for Sn-based perovskite fabrication, a series of natural antioxidants are studied as additives and ascorbic acid (VitC) is found to have a superior ability to inhibit the oxidation problem. A common cyclic molecule, 18-Crown-6, is further added as a second additive, which synergizes with VitC to significantly reduce the nonradiative recombination pathways in the PEA2SnI4 film. This synergistic effect greatly improves the performance of 2D red Sn-based PeLED, with a maximum external quantum efficiency of 1.87% (≈9 times that of the pristine device), a purer color, and better bias stability. This work demonstrates the potential of the dual-additive approach in enhancing the performance of 2D Sn-based PeLEDs, while the use of these environmentally friendly additives contributes to their future sustainability.

Dual-Adaptive Heterojunction Synaptic Transistors for Efficient Machine Vision in Harsh Lighting Conditions

Photoadaptive synaptic devices enable in-sensor processing of complex illumination scenes, while second-order adaptive synaptic plasticity improves learning efficiency by modifying the learning rate in a given environment. The integration of above adaptations in one phototransistor device will provide opportunities for developing high-efficient machine vision system. Here, a dually adaptable organic heterojunction transistor as a working unit in the system, which facilitates precise contrast enhancement and improves convergence rate under harsh lighting conditions, is reported. The photoadaptive threshold sliding originates from the bidirectional photoconductivity caused by the light intensity-dependent photogating effect. Metaplasticity is successfully implemented owing to the combination of ambipolar behavior and charge trapping effect. By utilizing the transistor array in a machine vision system, the details and edges can be highlighted in the 0.4% low-contrast images, and a high recognition accuracy of 93.8% with a significantly promoted convergence rate by about 5 times are also achieved. These results open a strategy to fully implement metaplasticity in optoelectronic devices and suggest their vision processing applications in complex lighting scenes.

Modulating Nucleation and Crystal Growth of Tin Perovskite Films for Efficient Solar Cells

The performance of tin halide perovskite solar cells (PSCs) has been severely limited by the rapid crystallization of tin perovskites, which usually leads to an undesirable film quality. In this work, we tackle this issue by regulating the nucleation and crystal growth of tin perovskite films using a small Lewis base additive, urea. The urea-SnI2 interaction facilitates the formation of larger and more uniform clusters, thus accelerating the nucleation process. Additionally, the crystal growth process is extended, resulting in a high-quality tin perovskite film with compact morphology, increased crystallinity, and reduced defects. Consequently, the efficiency of tin PSCs is significantly increased from 10.42% to 14.22%. This work highlights the importance of manipulating the nucleation and crystal growth of tin perovskites to realize efficient tin PSCs.

Efficient Homojunction Tin Perovskite Solar Cells Enabled by Gradient Germanium Doping

P-type self-doping is known to hamper tin-based perovskites for developing high-performance solar cells by increasing the background current density and carrier recombination processes. In this work, we propose a gradient homojunction structure with germanium doping that generates an internal electric field across the perovskite film to deplete the charge carriers. This structure reduces the dark current density of perovskite by over 2 orders of magnitude and trap density by an order of magnitude. The resultant tin-based perovskite solar cells exhibit a higher power conversion efficiency of 13.3% and excellent stability, maintaining 95% and 85% of their initial efficiencies after 250 min of continuous illumination and 3800 h of storage, respectively. We reveal the homojunction formation mechanism using density functional theory calculations and molecular level characterizations. Our work provides a reliable strategy for controlling the spatial energy levels in tin perovskite films and offers insights into designing intriguing lead-free perovskite optoelectronics.

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 %.

Narrow Bandgap Metal Halide Perovskites for All-Perovskite Tandem Photovoltaics

All-perovskite tandem solar cells are attracting considerable interest in photovoltaics research, owing to their potential to surpass the theoretical efficiency limit of single-junction cells, in a cost-effective sustainable manner. Thanks to the bandgap-bowing effect, mixed tin-lead (Sn-Pb) perovskites possess a close to ideal narrow bandgap for constructing tandem cells, matched with wide-bandgap neat lead-based counterparts. The performance of all-perovskite tandems, however, has yet to reach its efficiency potential. One of the main obstacles that need to be overcome is the─oftentimes─low quality of the mixed Sn-Pb perovskite films, largely caused by the facile oxidation of Sn(II) to Sn(IV), as well as the difficult-to-control film crystallization dynamics. Additional detrimental imperfections are introduced in the perovskite thin film, particularly at its vulnerable surfaces, including the top and bottom interfaces as well as the grain boundaries. Due to these issues, the resultant device performance is distinctly far lower than their theoretically achievable maximum efficiency. Robust modifications and improvements to the surfaces of mixed Sn-Pb perovskite films are therefore critical for the advancement of the field. This Review describes the origins of imperfections in thin films and covers efforts made so far toward reaching a better understanding of mixed Sn-Pb perovskites, in particular with respect to surface modifications that improved the efficiency and stability of the narrow bandgap solar cells. In addition, we also outline the important issues of integrating the narrow bandgap subcells for achieving reliable and efficient all-perovskite double- and multi-junction tandems. Future work should focus on the characterization and visualization of the specific surface defects, as well as tracking their evolution under different external stimuli, guiding in turn the processing for efficient and stable single-junction and tandem solar cell devices.

Suppressing Oxidation at Perovskite-NiOx Interface for Efficient and Stable Tin Perovskite Solar Cells

Inorganic nickel oxide (NiOx) is an ideal hole transport material (HTM) for the fabrication of high-efficiency, stable, and large-area perovskite photovoltaic devices because of its low cost, stability, and ease of solution processing. However, it delivers low power conversion efficiency (PCE) in tin perovskite solar cells (TPSCs) compared to other organic HTMs. Here, the origin of hole transport barriers at the perovskite-NiOx interface is identified and a self-assembled monolayer interface modification is developed, through introducing (4-(7H-dibenzo[c,g]carbazol-7-yl)ethyl)phosphonic acid (2PADBC) into the perovskite-NiOx interface. The 2PADBC anchors undercoordinated Ni cations through phosphonic acid groups, suppressing the reaction of highly active Ni≥3+ defects with perovskites, while increasing the electron density and oxidation activation energy of Sn at the perovskite interface, reducing the interface nonradiative recombination caused by tetravalent Sn defects. The devices deliver significantly increased open-circuit voltage from 0.712 to 0.825 V, boosting the PCE to 14.19% for the small-area device and 12.05% for the large-area (1 cm2) device. In addition, the 2PADBC modification enhances the operational stability of NiOx-based TPSCs, maintaining more than 93% of their initial efficiency after 1000 h.

B-Site Co-Doping Coupled with Additive Passivation Pushes the Efficiency of Pb-Sn Mixed Inorganic Perovskite Solar Cells to Over 17

Pb-Sn mixed inorganic perovskite solar cells (PSCs) have garnered increasing interest as a viable solution to mitigate the thermal instability and lead toxicity of hybrid lead-based PSCs. However, the relatively poor structural stability and low device efficiency hinder its further development. Herein, high-performance manganese (Mn)-doped Pb-Sn-Mn-based inorganic perovskite solar cells (PSCs) are successfully developed by introducing Benzhydroxamic Acid (BHA) as multifunctional additive. The incorporation of smaller divalent Mn cations contributes to a contraction of the perovskite crystal, leading to an improvement in structural stability. The BHA additive containing a reductive hydroxamic acid group (O═C-NHOH) not only mitigates the notorious oxidation of Sn2+ but also interacts with metal ions at the B-site and passivates related defects. This results in films with high crystallinity and low defect density. Moreover, the BHA molecules tend to introduce a near-vertical dipole moment that parallels the built-in electric field, thus facilitating charge carrier extraction. Consequently, the resulting device delivers a champion PCE as high as 17.12%, which represents the highest reported efficiency for Pb-Sn-based inorganic PSCs thus far. Furthermore, the BHA molecule provides an in situ encapsulation of the perovskite grain boundary, resulting in significant enhancement of device air stability.

Self-Assembled Monolayers for Interfacial Engineering in Solution-Processed Thin-Film Electronic Devices: Design, Fabrication, and Applications

Interfacial engineering has long been a vital means of improving thin-film device performance, especially for organic electronics, perovskites, and hybrid devices. It greatly facilitates the fabrication and performance of solution-processed thin-film devices, including organic field effect transistors (OFETs), organic solar cells (OSCs), perovskite solar cells (PVSCs), and organic light-emitting diodes (OLEDs). However, due to the limitation of traditional interfacial materials, further progress of these thin-film devices is hampered particularly in terms of stability, flexibility, and sensitivity. The deadlock has gradually been broken through the development of self-assembled monolayers (SAMs), which possess distinct benefits in transparency, diversity, stability, sensitivity, selectivity, and surface passivation ability. In this review, we first showed the evolution of SAMs, elucidating their working mechanisms and structure-property relationships by assessing a wide range of SAM materials reported to date. A comprehensive comparison of various SAM growth, fabrication, and characterization methods was presented to help readers interested in applying SAM to their works. Moreover, the recent progress of the SAM design and applications in mainstream thin-film electronic devices, including OFETs, OSCs, PVSCs and OLEDs, was summarized. Finally, an outlook and prospects section summarizes the major challenges for the further development of SAMs used in thin-film devices.

An open-cage bis[60]fulleroid as an electron transport material for tin halide perovskite solar cells

An open-cage bis[60]fulleroid (OC) was applied as an electron transport material (ETM) in tin (Sn) halide perovskite solar cells (PSCs). Due to the reduced offset between the energy levels of Sn-based perovskites and ETMs, the power conversion efficiency (PCE) of Sn-based PSCs with OC reached 9.6% with an open-circuit voltage (VOC) of 0.72 V. Additionally, OC exhibited superior thermal stability and provided 75% of the material without decomposition after vacuum deposition. The PSC using vacuum-deposited OC as the ETM could afford a PCE of 7.6%, which is a big leap forward compared with previous results using vacuum-deposited fullerene derivatives as ETMs.

Efficient Tin-Based Perovskite Solar Cell with a Cesium Acetate Pre-buried PEDOT:PSS Hole Transport Layer

The strong Lewis acid tin halide leads to an excessively fast crystallization rate, resulting in more defects in the film and degraded device performance. In this work, a cesium acetate (CsAc) pre-buried poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layer acts as nucleation points during the crystallization of tin-based perovskite, which can induce preferential orientation growth of crystals and increase the grain size to improve the quality of crystallization. The addition of CsAc not only can increase the conductivity of PEDOT:PSS but also can improve the wettability of the perovskite precursor solution to enhance the interface contact between the hole transport layer and perovskite layer. Because of the incorporation of CsAc in PEDOT:PSS, the average short-circuit current density increases from 23.80 to 27.60 mA cm-2. Furthermore, a power conversion efficiency of 10.99% is achieved for a tin-based perovskite solar cell with CsAc-doped PEDOT:PSS as the hole transport layer.

Multifunctional Buried Interface Modification Enables Efficient Tin Perovskite Solar Cells

Tin perovskite solar cells (PSCs) are considered promising candidates to promote lead-free perovskite photovoltaics. However, their power conversion efficiency (PCE) is limited by the easy oxidation of Sn2+ and low quality of tin perovskite film. Herein, an ultra-thin 1-carboxymethyl-3-methylimidazolium chloride (ImAcCl) layer is used to modify the buried interface in tin PSCs, which can induce multifunctional improvements and remarkably enhance the PCE. The carboxylate group (CO) and the hydrogen bond donor (NH) in ImAcCl can interact with tin perovskites, thus significantly suppressing the oxidation of Sn2+ and reducing the trap density in perovskite films. The interfacial roughness is reduced, which contributes to a high-quality tin perovskite film with increased crystallinity and compactness. In addition, the buried interface modification can modulate the crystal dimensionality, favoring the formation of large bulk-like crystals instead of low-dimensional ones in tin perovskite films. Therefore, the charge carrier transport is effectively promoted and the charge carrier recombination is suppressed. Eventually, tin PSCs show a remarkably enhanced PCE from 10.12% to 12.08%. This work highlights the importance of buried interface engineering and provides an effective way to realize efficient tin PSCs.

Efficient Tin-Based Perovskite Solar Cells Enabled by Precisely Synthesized Single-Isomer Fullerene Bisadducts with Regulated Molecular Packing

Designing and synthesizing fullerene bisadducts with a higher-lying conduction band minimum is promising to further improve the device performance of tin-based perovskite solar cells (TPSCs). However, the commonly obtained fullerene bisadduct products are isomeric mixtures and require complicated separation. Moreover, the isomeric mixtures are prone to resulting in energy alignment disorders, interfacial charge loss, and limited device performance improvement. Herein, we synthesized single-isomer C60- and C70-based diethylmalonate functionalized bisadducts (C60BB and C70BB) by utilizing the steric-hindrance-assisted strategy and determined all molecular structures involved by single crystal diffraction. Meanwhile, we found that the different solvents used for processing the fullerene bisadducts can effectively regulate the molecular packing in their films. The dense and amorphous fullerene bisadduct films prepared by using anisole exhibited the highest electron mobility. Finally, C60BB- and C70BB-based TPSCs showed impressive efficiencies up to 14.51 and 14.28%, respectively. These devices also exhibited excellent long-term stability. This work highlights the importance of developing strategies to synthesize single-isomer fullerene bisadducts and regulate their molecular packing to improve TPSCs' performance.

Ternary-Metal Sn-Pb-Zn Perovskite to Reconstruct Top Surface for Efficient and Stable Less-Pb Perovskite Solar Cells

Though Sn-Pb alloyed perovskite solar cells (PSCs) achieved great progress, there is a dilemma to further increase Sn for less-Pb requirement. High Sn ratio (>70%) perovskite exhibits nonstoichiometric Sn:Pb:I at film surface to aggravate Sn2+ oxidation and interface energy mismatch. Here, ternary metal alloyed (FASnI3 )0.7 (MAPb1- x Znx I3 )0.3 (x = 0-3%) is constructed for Pb% < 30% perovskite. Zn with smaller ionic size and stronger ionic interaction than Sn/Pb assists forming high-quality perovskite film with ZnI6 4- enriched at surface to balance Sn:Pb:I ratio. Differing from uniform bulk doping, surface-rich Zn with lower lying orbits pushes down the energy band of perovskite and adjusts the interface energy for efficient charge transfer. The alloyed PSC realizes efficiency of 19.4% at AM1.5 (one of the highest values reported for Pb% < 30% PSCs). Moreover, stronger bonding of Zn─I and Sn─I contributes to better durability of ternary perovskite than binary perovskite. This work highlights a novel alloy method for efficient and stable less-Pb PSCs.

Scalable Solution-Processed Hybrid Electron Transport Layers for Efficient All-Perovskite Tandem Solar Modules

All-perovskite tandem solar cells offer the potential to surpass the Shockley-Queisser (SQ) limit efficiency of single-junction solar cells while maintaining the advantages of low-cost and high-productivity solution processing. However, scalable solution processing of electron transport layer (ETL) in p-i-n structured perovskite solar subcells remains challenging due to the rough perovskite film surface and energy level mismatch between ETL and perovskites. Here, scalable solution processing of hybrid fullerenes (HF) with blade-coating on both wide-bandgap (≈1.80 eV) and narrow-bandgap (≈1.25 eV) perovskite films in all-perovskite tandem solar modules is developed. The HF, comprising a mixture of fullerene (C60 ), phenyl C61 butyric acid methyl ester, and indene-C60 bisadduct, exhibits improved conductivity, superior energy level alignment with both wide- and narrow-bandgap perovskites, and reduced interfacial nonradiative recombination when compared to the conventional thermal-evaporated C60 . With scalable solution-processed HF as the ETLs, the all-perovskite tandem solar modules achieve a champion power conversion efficiency of 23.3% (aperture area = 20.25 cm2 ). This study paves the way to all-solution processing of low-cost and high-efficiency all-perovskite tandem solar modules in the future.

Grain Engineering of Sb2 S3 Thin Films to Enable Efficient Planar Solar Cells with High Open-Circuit Voltage

Sb2 S3 is a promising environmentally friendly semiconductor for high performance solar cells. But, like many other polycrystalline materials, Sb2 S3 is limited by nonradiative recombination and carrier scattering by grain boundaries (GBs). This work shows how the GB density in Sb2 S3 films can be significantly reduced from 1068 ± 40 to 327 ± 23 nm µm-2 by incorporating an appropriate amount of Ce3+ into the precursor solution for Sb2 S3 deposition. Through extensive characterization of structural, morphological, and optoelectronic properties, complemented with computations, it is revealed that a critical factor is the formation of an ultrathin Ce2 S3 layer at the CdS/Sb2 S3 interface, which can reduce the interfacial energy and increase the adhesion work between Sb2 S3 and the substrate to encourage heterogeneous nucleation of Sb2 S3 , as well as promote lateral grain growth. Through reductions in nonradiative recombination at GBs and/or the CdS/Sb2 S3 heterointerface, as well as improved charge-carrier transport properties at the heterojunction, this work achieves high performance Sb2 S3 solar cells with a power conversion efficiency reaching 7.66%. An impressive open-circuit voltage (VOC ) of 796 mV is achieved, which is the highest reported thus far for Sb2 S3 solar cells. This work provides a strategy to simultaneously regulate the nucleation and growth of Sb2 S3 absorber films for enhanced device performance.

On the Durability of Tin-Containing Perovskite Solar Cells

Tin (Sn)-containing perovskite solar cells (PSCs) have gained significant attention in the field of perovskite optoelectronics due to lower toxicity than their lead-based counterparts and their potential for tandem applications. However, the lack of stability is a major concern that hampers their development. To achieve the long-term stability of Sn-containing PSCs, it is crucial to have a clear and comprehensive understanding of the degradation mechanisms of Sn-containing perovskites and develop mitigation strategies. This review provides a compendious overview of degradation pathways observed in Sn-containing perovskites, attributing to intrinsic factors related to the materials themselves and environmental factors such as light, heat, moisture, oxygen, and their combined effects. The impact of interface and electrode materials on the stability of Sn-containing PSCs is also discussed. Additionally, various strategies to mitigate the instability issue of Sn-containing PSCs are summarized. Lastly, the challenges and prospects for achieving durable Sn-containing PSCs are presented.

Dopant engineering for ZnO electron transport layer towards efficient perovskite solar cells

The conventional electron transport layer (ETL) TiO2 has been widely used in perovskite solar cells (PSCs), which have produced exceptional power conversion efficiencies (PCE), allowing the technology to be highly regarded and propitious. Nevertheless, the recent high demand for energy harvesters in wearable electronics, aerospace, and building integration has led to the need for flexible solar cells. However, the conventional TiO2 ETL layer is less preferred, where a crystallization process at a temperature as high as 450 °C is required, which degrades the plastic substrate. Zinc oxide nanorods (ZnO NRs) as a simple and low-cost fabrication material may fulfil the need as an ETL, but they still suffer from low PCE due to atomic defect vacancy. To delve into the issue, several dopants have been reviewed as an additive to passivate or substitute the Zn2+ vacancies, thus enhancing the charge transport mechanism. This work thereby unravels and provides a clear insight into dopant engineering in ZnO NRs ETL for PSC.

Multifunctional Fiber-Based Optoacoustic Emitter as a Bidirectional Brain Interface

A bidirectional brain interface with both "write" and "read" functions can be an important tool for fundamental studies and potential clinical treatments for neurological diseases. Herein, a miniaturized multifunctional fiber-based optoacoustic emitter (mFOE) is reported thatintegrates simultaneous optoacoustic stimulation for "write" and electrophysiology recording of neural circuits for "read". Because of the intrinsic ability of neurons to respond to acoustic wave, there is no requirement of the viral transfection. The orthogonality between optoacoustic waves and electrical field provides a solution to avoid the interference between electrical stimulation and recording. The stimulation function of the mFOE is first validated in cultured ratcortical neurons using calcium imaging. In vivo application of mFOE for successful simultaneous optoacoustic stimulation and electrical recording of brain activities is confirmed in mouse hippocampus in both acute and chronical applications up to 1 month. Minor brain tissue damage is confirmed after these applications. The capability of simultaneous neural stimulation and recording enabled by mFOE opens up new possibilities for the investigation of neural circuits and brings new insights into the study of ultrasound neurostimulation.

A Newly Crosslinked-double Network PEDOT:PSS@PEGDMA toward Highly-Efficient and Stable Tin-Lead Perovskite Solar Cells

Until now, poly(3,4-ethylenedioxythiophene):poly(styrensulfonate) (PEDOT:PSS) is widely used in Sn-Pb perovskite solar cells (PSCs) due to its many advantages, including high optical transparency, suitable conductivity, superior wettability, and so on. However, the acidic and hydroscopic properties of the PSS component, as well as the incongruous energy level of the hole transport layer (HTL), may lead to unsatisfying interface properties and decreased device performance. Herein, by adding polyethylene glycol dimethacrylate (PEGDMA) into PEDOT:PSS, a newly crosslinked-double-network obtain of PEDOT:PSS@PEGDMA film, which could not only optimize nucleation and crystallinity of Sn-Pb perovskite films, but also suppress defect density and optimize energy level alignment at the HTL/perovskite interface. As a result, the achieves highly efficient and stable mixed Sn-Pb PSCs with an encouraging power conversion efficiency of 20.9%. Additionally, the device can maintain good stability under N2 atmosphere.

Mutually Tuned Dual Additive Engineering Synergistically Enhances the Photovoltaic Performance of Tin-Based Perovskite Solar Cells

Tin-based perovskite solar cells (T-PSCs) have become the star photovoltaic products in recent years due to their low environmental toxicity and superior photovoltaic performance. However, the easy oxidation of Sn2+ and the energy level mismatch between the perovskite film and charge transport layer limit its efficiency. In order to regulate the microstructure and photoelectric properties of tin-based perovskite films to enhance the efficiency and stability of T-PSCs, guanidinium bromide (GABr) and organic Lewis-based additive methylamine cyanate (MAOCN) are introduced into the FA0.9PEA0.1SnI3-based perovskite precursor. A series of characterizations show that the interactions between additive molecules and perovskite mutually reconcile to improve the photovoltaic performance of T-PSCs. The introduction of GABr can adjust the band gap of the perovskite film and energy level alignment of T-PSCs. They significantly increase the open-circuit voltage (Voc). The MAOCN material can form hydrogen bonds with SnI2 in the precursor, which can inhibit the oxidation of Sn2+ and significantly improve the short-circuit current density (Jsc). The synergistic modulation of the dual additives reduces the trap-state density and improves photovoltaic performance, resulting in an increased champion efficiency of 9.34 for 5.22% of the control PSCs. The unencapsulated T-PSCs with GABr and MAOCN dual additives prepared in the optimized process can retain more than 110% of their initial efficiency after aging for 1750 h in a nitrogen glovebox, but the control PSCs maintain only 50% of their initial efficiency kept in the same conditions. This work provides a new perspective to further improve the efficiency and stability of T-PSCs.

Carrier Modulation via Tunnel Oxide Passivating at Buried Perovskite Interface for Stable Carbon-Based Solar Cells

Carbon-based perovskite solar cells (C-PSCs) have the impressive characteristics of good stability and potential commercialization. The insulating layers play crucial roles in charge modulation at the buried perovskite interface in mesoporous C-PSCs. In this work, the effects of three different tunnel oxide layers on the performance of air-processed C-PSCs are scrutinized to unveil the passivating quality. Devices with ZrO2-passivated TiO2 electron contacts exhibit higher power conversion efficiencies (PCEs) than their Al2O3 and SiO2 counterparts. The porous feature and robust chemical properties of ZrO2 ensure the high quality of the perovskite absorber, thus ensuring the high repeatability of our devices. An efficiency level of 14.96% puts our device among the state-of-the-art hole-conductor-free C-PSCs, and our unencapsulated device maintains 88.9% of its initial performance after 11,520 h (480 days) of ambient storage. These results demonstrate that the function of tunnel oxides at the perovskite/electron contact interface is important to manipulate the charge transfer dynamics that critically affect the performance and stability of C-PSCs.

Synergic Electron and Defect Compensation Minimizes Voltage Loss in Lead-Free Perovskite Solar Cells

Sn perovskite solar cells have been regarded as one of the most promising alternatives to the Pb-based counterparts due to their low toxicity and excellent optoelectronic properties. However, the Sn perovskites are notorious to feature heavy p-doping characteristics and possess abundant vacancy defects, which result in under-optimized interfacial energy level alignment and severe nonradiative recombination. Here, we reported a synergic "electron and defect compensation" strategy to simultaneously modulate the electronic structures and defect profiles of Sn perovskites via incorporating a traced amount (0.1 mol %) of heterovalent metal halide salts. Consequently, the doping level of modified Sn perovskites was altered from heavy p-type to weak p-type (i.e. up-shifting the Fermi level by ∼0.12 eV) that determinately reducing the barrier of interfacial charge extraction and effectively suppressing the charge recombination loss throughout the bulk perovskite film and at relevant interfaces. Pioneeringly, the resultant device modified with electron and defect compensation realized a champion efficiency of 14.02 %, which is ∼46 % higher than that of control device (9.56 %). Notably, a record-high photovoltage of 1.013 V was attained, corresponding to the lowest voltage deficit of 0.38 eV reported to date, and narrowing the gap with Pb-based analogues (∼0.30 V).

Two-Second-Annealed 2D/3D Perovskite Films with Graded Energy Funnels and Toughened Heterointerfaces for Efficient and Durable Solar Cells

The 2D/3D perovskite heterostructures have been widely investigated to enhance the efficiency and stability of perovskite solar cells (PSCs). However, rational manipulation of phase distribution and energy level alignment in such 2D/3D perovskite hybrids are still of great challenge. Herein, we successfully achieved spontaneous phase alignment of 2D/3D perovskite heterostructures by concurrently introducing both 2D perovskite component and organic halide additive. The graded phase distribution of 2D perovskites with different n values and 3D perovskites induced favorable energy band alignment across the perovskite film and boosted the charge transfer at the relevant heterointerfaces. Moreover, the 2D perovskite component also acted as a "band-aid" to simultaneously passivate the defects and release the residual tensile stress of perovskite films. Encouragingly, the blade-coated PSCs based on only ≈2 s in-situ fast annealed 2D/3D perovskite films with favorable energy funnels and toughened heterointerfaces achieved promising efficiencies of 22.5 %, accompanied by extended lifespan. To our knowledge, this is the highest reported efficiency for the PSCs fabricated with energy-saved thermal treatment just within a few seconds, which also outperformed those state-of-the-art annealing-free analogues. Such a two-second-in-situ-annealing technique could save the energy cost by up to 99.6 % during device fabrication, which will grant its low-coast implementation.

Morphology and Performance Enhancement through the Strong Passivation Effect of Amphoteric Ions in Tin-based Perovskite Solar Cells

Despite the optoelectronic similarities between tin and lead halide perovskites, the performance of tin-based perovskite solar cells remains far behind, with the highest reported efficiency to date being ≈14%. This is highly correlated to the instability of tin halide perovskite, as well as the rapid crystallization behavior in perovskite film formation. In this work, l-Asparagine as a zwitterion plays a dual role in controlling the nucleation/crystallization process and improving the morphology of perovskite film. Furthermore, tin perovskites with l-Asparagine show more favorable energy-level matching, enhancing the charge extraction and minimizing the charge recombination, leading to an enhanced power conversion efficiency of 13.31% (from 10.54% without l-Asparagine) with remarkable stability. These results are also in good agreement with the density functional theory calculations. This work not only provides a facile and efficient approach to controlling the crystallization and morphology of perovskite film but also offers guidelines for further improved performance of tin-based perovskite electronic devices.

Highly Efficient HTM-Free Tin Perovskite Solar Cells with Outstanding Stability Exceeding 10000 h

The bottleneck in the rapid development of tin-based perovskite solar cells (TPSCs) is the inherent chemical instability. Although this is being addressed continuously, the device performance has not improved further due to the use of PEDOT:PSS as the hole-transport material (HTM), which has poor long-term stability. Herein we have applied commercial ITO nanoparticles over ITO glass substrates and altered the surface chemistry of the ITO electrode via a simple two-step thermal annealing, followed by a UV-ozone treatment. These surface-modified ITO electrodes display promising interfacial characteristics, such as a suitable band alignment owing to significantly reduced surface carbon contamination, increased In-O bonding, and reduced oxygen vacancies, that enabled fabrication of an HTM-free TPSC device according to a two-step method. The fabricated device possessed an outstanding power conversion efficiency (PCE) of 9.7%, along with a superior long-term stability by retaining over 90% of the initial PCE upon shelf storage in a glovebox for a period of over 10000 h. The application of ITO nanoparticles led to effective interfacial passivation, whose impacts on the long-term durability were assessed using electrochemical impedance spectroscopy, time-resolved photoluminescence decay profiles, and femtosecond transient absorption spectroscopy techniques.

Tin Halide Perovskite Solar Cells with Open-Circuit Voltages Approaching the Shockley-Queisser Limit

The power conversion efficiency of tin-based halide perovskite solar cells is limited by large photovoltage losses arising from the significant energy-level offset between the perovskite and the conventional electron transport material, fullerene C₆₀. The fullerene derivative indene-C₆₀ bisadduct (ICBA) is a promising alternative to mitigate this drawback, owing to its superior energy level matching with most tin-based perovskites. However, the less finely controlled energy disorder of the ICBA films leads to the extension of its band tails that limits the photovoltage of the resultant devices and reduces the power conversion efficiency. Herein, we fabricate ICBA films with improved morphology and electrical properties by optimizing the choice of solvent and the annealing temperature. Energy disorder in the ICBA films is substantially reduced, as evidenced by the 22 meV smaller width of the electronic density of states. The resulting solar cells show open-circuit voltages of up to 1.01 V, one of the highest values reported so far for tin-based devices. Combined with surface passivation, this strategy enabled solar cells with efficiencies of up to 11.57%. Our work highlights the importance of controlling the properties of the electron transport material toward the development of efficient lead-free perovskite solar cells and demonstrates the potential of solvent engineering for efficient device processing.

Chemical Bridge-Mediated Heterojunction Electron Transport Layers Enable Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) emerged as potential photovoltaic energy-generating devices developing in recent years because of their excellent photovoltaic properties and ease of processing. However, PSCs are still reporting efficiencies much lower than their theoretical limits owing to various losses caused by the charge transport layer and the perovskite. In this regard, herein, an interface engineering strategy using functional molecules and chemical bridges was applied to reduce the loss of the heterojunction electron transport layer. As a functional interface layer, ethylenediaminetetraacetic acid (EDTA) was introduced between PCBM and the ZnO layer, and as a result, EDTA simultaneously formed chemical bonds with PCBM and ZnO to serve as a chemical bridge connecting the two. DFT and chemical analyses revealed that EDTA can act as a chemical bridge between PCBM and ZnO, passivate defect sites, and improve charge transfer. Optoelectrical analysis proved that EDTA chemical bridge-mediated charge transfer (CBM-CT) provides more efficient interfacial charge transport by reducing trap-assisted recombination losses at ETL interfaces, thereby improving device performance. The PSC with EDTA chemical bridge-mediated heterojunction ETL exhibited a high PCE of 21.21%, almost no hysteresis, and excellent stability to both air and light.

Hole Transport Materials for Tin-Based Perovskite Solar Cells: Properties, Progress, Prospects

The power conversion efficiency of modern perovskite solar cells has surpassed that of commercial photovoltaic technology, showing great potential for commercial applications. However, the current high-performance perovskite solar cells all contain toxic lead elements, blocking their progress toward industrialization. Lead-free tin-based perovskite solar cells have attracted tremendous research interest, and more than 14% power conversion efficiency has been achieved. In tin-based perovskite, Sn²⁺ is easily oxidized to Sn⁴⁺ in air. During this process, two additional electrons are introduced to form a heavy p-type doping perovskite layer, necessitating the production of hole transport materials different from that of lead-based perovskite devices or organic solar cells. In this review, for the first time, we summarize the hole transport materials used in the development of tin-based perovskite solar cells, describe the impact of different hole transport materials on the performance of tin-based perovskite solar cell devices, and summarize the recent progress of hole transport materials. Lastly, the development direction of lead-free tin-based perovskite devices in terms of hole transport materials is discussed based on their current development status. This comprehensive review contributes to the development of efficient, stable, and environmentally friendly tin-based perovskite devices and provides guidance for the hole transport layer material design.

Prospects for Tin-Containing Halide Perovskite Photovoltaics

Tin-containing metal halide perovskites have enormous potential as photovoltaics, both in narrow band gap mixed tin-lead materials for all-perovskite tandems and for lead-free perovskites. The introduction of Sn(II), however, has significant effects on the solution chemistry, crystallization, defect states, and other material properties in halide perovskites. In this perspective, we summarize the main hurdles for tin-containing perovskites and highlight successful attempts made by the community to overcome them. We discuss important research directions for the development of these materials and propose some approaches to achieve a unified understanding of Sn incorporation. We particularly focus on the discussion of charge carrier dynamics and nonradiative losses at the interfaces between perovskite and charge extraction layers in p-i-n cells. We hope these insights will aid the community to accelerate the development of high-performance, stable single-junction tin-containing perovskite solar cells and all-perovskite tandems.

Sn-Based Perovskite Solar Cells towards High Stability and Performance

Recent years have witnessed rapid development in the field of tin-based perovskite solar cells (TPSCs) due to their environmental friendliness and tremendous potential in the photovoltaic field. Most of the high-performance PSCs are based on lead as the light-absorber material. However, the toxicity of lead and the commercialization raise concerns about potential health and environmental hazards. TPSCs can maintain all the optoelectronic properties of lead PSCs, as well as feature a favorable smaller bandgap. However, TPSCs tend to undergo rapid oxidation, crystallization, and charge recombination, which make it difficult to unlock the full potential of such perovskites. Here, we shed light on the most critical features and mechanisms affecting the growth, oxidation, crystallization, morphology, energy levels, stability, and performance of TPSCs. We also investigate the recent strategies, such as interfaces and bulk additives, built-in electric field, and alternative charge transport materials that are used to enhance the performance of the TPSCs. More importantly, we have summarized most of the recent best-performing lead-free and lead-mixed TPSCs. This review aims to help future research in TPSCs to produce highly stable and efficient solar cells.

Surface energy and surface stability of cesium tin halide perovskites: a theoretical investigation

Lead halide perovskites have been widely studied in the fields of photovoltaics and optoelectronics for over a decade. The toxicity of lead poses a big challenge to the potential applications of the materials. In recent years, lead-free halide perovskites have received significant attention due to their excellent optoelectronic properties and environment-friendly character. Tin halide perovskites have emerged as one of the most promising candidates for lead-free optoelectronic materials. It is of fundamental importance to understand the surface properties of tin halide perovskites that remain largely unknown. Using the density functional theory (DFT) method, we explore the surface energy and surface stability of low-index surfaces of cubic CsSnX₃ (X = Cl, Br, I), i.e., (100), (110), and (111) surfaces. We calculate the stability phase diagrams of these surfaces and find that the (100) surface is more stable than the (110) and (111) surfaces. Interestingly, Br₂-terminated (110) and CsBr₃-terminated (111) polar surfaces are relatively more stable in CsSnBr₃ than those in CsPbBr₃ due to a higher level of valence band maximum and thus lesser energy cost in removing electrons to compensate for the polarity of the former. We calculate the surface energies of CsSnX₃ surfaces that are difficult to access from experiments. The surface energies are very low in comparison with that of oxide perovskites. The origin of this lies in the relatively low binding strength of halide perovskites because of the soft nature of their structures. Furthermore, the connection between exfoliation energy and the cleavage energy in CsSnX₃ is discussed.

Substitution of Ethylammonium Halides Enabling Lead-Free Tin-Based Perovskite Solar Cells with Enhanced Efficiency and Stability

Tin (Sn)-based perovskite solar cells (PSCs) have attracted extensive attention due to the irlow toxicity and excellent optoelectric properties. Nonetheless, the development of Sn-based PSCs is still hampered by poor film quality due to the fast crystallization and the oxidation from Sn²⁺ to Sn⁴⁺. In this work, we compare and employ three ethylammonium halides, EAX (X = Cl, Br, I) to explore their roles in Sn-based perovskites and solar cells. We find that crystallinity and crystallization orientation of perovskites are optimized with the regulation of EAI. EABr leads to reduced defect density and enhanced crystallinity but also the lowest absorption and the widest band gap owing to the substitution of Br^-. Notably, perovskites with EACl exhibit the best crystallinity, lowest defect density, and excellent antioxidant capacity benefiting from the partial substitution of Cl^-. Consequently, the EACl-modified device achieves a champion PCE of 12.50% with an improved V_oc of 0.79 V. Meanwhile, an unencapsulated EACl device shows excellent shelf stability with negligible efficiency degradation after 5400 h of storage in a N₂-filled glovebox, and the encapsulated device retains its initial efficiency after continuous light illumination at the maximum power point for 100 h in air.

Well-Defined Fullerene Bisadducts Enable High-Performance Tin-Based Perovskite Solar Cells

Tin-based perovskite solar cells (TPSCs) are attracting intense research interest due to their excellent optoelectric properties and eco-friendly features. To further improve the device performance, developing new fullerene derivatives as electron transporter layers (ETLs) is highly demanded. Four well-defined regioisomers (trans-2, trans-3, trans-4, and e) of diethylmalonate-C₆₀ bisadduct (DCBA) are isolated and well characterized. The well-defined molecular structure enables us to investigate the real structure-dependent effects on photovoltaic performance. It is found that the chemical structures of the regioisomers not only affect their energy levels, but also lead to significant differences in their molecular packings and interfacial contacts. As a result, the devices with trans-2, trans-3, trans-4, and e as ETLs yield efficiencies of 11.69%, 14.58%, 12.59%, and 10.55%, respectively, which are higher than that of the as-prepared DCBA-based (10.28%) device. Notably, the trans-3-based device also demonstrates a certified efficiency of 14.30%, representing one of the best-performing TPSCs.

Certified high-efficiency "large-area" perovskite solar module for Fresnel lens-based concentrated photovoltaics

The future of energy generation is well in tune with the critical needs of the global economy, leading to more green innovations and emissions-abatement technologies. Introducing concentrated photovoltaics (CPVs) is one of the most promising technologies owing to its high photo-conversion efficiency. Although most researchers use silicon and cadmium telluride for CPV, we investigate the potential in nascent technologies, such as perovskite solar cell (PSC). This work constitutes a preliminary investigation into a "large-area" PSC module under a Fresnel lens (FL) with a "refractive optical concentrator-silicon-on-glass" base to minimize the PV performance and scalability trade-off concerning the PSCs. The FL-PSC system measured the solar current-voltage characteristics in variable lens-to-cell distances and illuminations. The PSC module temperature was systematically studied using the COMSOL transient heat transfer mechanism. The FL-based technique for "large-area" PSC architectures is a promising technology that further facilitates the potential for commercialization.

A Review on the Progress, Challenges, and Performances of Tin-Based Perovskite Solar Cells

In this twenty-first century, energy shortages have become a global issue as energy demand is growing at an astounding rate while the energy supply from fossil fuels is depleting. Thus, the urge to develop sustainable renewable energy to replace fossil fuels is significant to prevent energy shortages. Solar energy is the most promising, accessible, renewable, clean, and sustainable substitute for fossil fuels. Third-generation (3G) emerging solar cell technologies have been popular in the research field as there are many possibilities to be explored. Among the 3G solar cell technologies, perovskite solar cells (PSCs) are the most rapidly developing technology, making them suitable for generating electricity efficiently with low production costs. However, the toxicity of Pb in organic-inorganic metal halide PSCs has inherent shortcomings, which will lead to environmental contamination and public health problems. Therefore, developing a lead-free perovskite solar cell is necessary to ensure human health and a pollution-free environment. This review paper summarized numerous types of Sn-based perovskites with important achievements in experimental-based studies to date.

Remarkable Stability and Optoelectronic Properties of an All-Inorganic CsSn0.5Ge0.5I3 Perovskite Solar Cell

Sn-Ge mixed perovskites have been proposed as promising lead-free candidates in the photovoltaics (PV) field. In this work, we discovered a stable P1 phase Sn-Ge mixed structure (CsSn_0.5Ge_0.5I₃) with an appropriate band gap value of 1.19 eV, which manifests its unique structural stability and physics properties. The thermodynamic stability of this mixed structure under different growth conditions and all possible native defects are depicted in detail. The formation energies and dominant native point defects indicate that P1 phase CsSn_0.5Ge_0.5I₃ exhibits unipolar self-doping behavior (p-type conductivity) and good defect tolerance while the growth condition changes. In addition, the calculation of light absorption confirmed that the P1 phase has a higher light absorption coefficient than that of MAPbI₃ in the visible light range, showing excellent light absorption. Our work not only provides theoretical guidance for unraveling the unusual structural stability of Sn-Ge mixed perovskites, but also offers a useful scheme to modulate the stability and optoelectronic properties of Ge-based perovskites through alloy engineering.

A Universal Surface Treatment for p-i-n Perovskite Solar Cells

Perovskite interfaces critically influence the final performance of the photovoltaic devices. Optimizing them by reducing the defect densities or improving the contact with the charge transporting material is key to further enhance the efficiency and stability of perovskite solar cells. Inverted (p-i-n) devices can particularly benefit here, as evident from various successful attempts. However, every reported strategy is adapted to specific cell structures and compositions, affecting their robustness and applicability by other researchers. In this work, we present the universality of perovskite top surface post-treatment with ethylenediammonium diiodide (EDAI₂) for p-i-n devices. To prove it, we compare devices bearing perovskite films of different composition, i.e., Sn-, Pb-, and mixed Sn-Pb-based devices, achieving efficiencies of up to 11.4, 22.0, and 22.9%, respectively. A careful optimization of the EDAI₂ thickness indicates a different tolerance for Pb- and Sn-based devices. The main benefit of this treatment is evident in the open-circuit voltage, with enhancements of up to 200 mV for some compositions. In addition, we prove that this treatment can be successfully applied by both wet (spin-coating) and dry (thermal evaporation) methods, regardless of the composition. The versatility of this treatment makes it highly appealing for industrial application, as it can be easily adapted to specific processing requirements. We present a detailed experimental protocol, aiming to provide the community with an easy, universal perovskite post-treatment method for reliably improving the device efficiency, highlighting the potential of interfaces for the field.

Environmental and health risks of perovskite solar modules: Case for better test standards and risk mitigation solutions

Perovskite solar cells (PSCs) promise high efficiencies and low manufacturing costs. Most formulations, however, contain lead, which raises health and environmental concerns. In this review, we use a risk assessment approach to identify and evaluate the technology risks to the environment and human health. We analyze the risks by following the technology from production to transportation to installation to disposal and examine existing environmental and safety regulations in each context. We review published data from leaching and air emissions testing and highlight gaps in current knowledge and a need for more standardization. Methods to avoid lead release through introduction of absorbing materials or use of alternative PSC formulations are reviewed. We conclude with the recommendation to develop recycling programs for PSCs and further standardized testing to understand risks related to leaching and fires.

Stirring-Time Control Approach to Manage Colloid Nucleation Size for the Fabrication of High-Performance Sn-Based Perovskite Solar Cells

Colloidal nucleation is first observed to exist in a Sn-based perovskite solution, and its components and size are discovered to alter in real time with stirring time. Then, a simple stirring-time control approach is developed to manage the size of the colloids, and with continuous stirring for 3 days an optimal colloid with size <10 nm is confirmed to successfully form a continuous, dense, high-quality perovskite film. Herein, the colloids exist in the form of [SnI₆]^4- complete coordination compounds, with which a compact FA_0.75MA_0.25SnI₃ perovskite film with reduced defects and enhanced crystallinity concentration is obtained as nucleation sites, and a planar inverted perovskite solar cell with a champion power conversion efficiency of 10.74% is eventually realized. This work provides a novel perspective to enhance perovskite film quality and thus device performance via controlling high-quality nucleation in precursor solution.

Engineering Stable Lead-Free Tin Halide Perovskite Solar Cells: Lessons from Materials Chemistry

Substituting toxic lead with tin (Sn) in perovskite solar cells (PSCs) is the most promising route toward the development of high-efficiency lead-free devices. Despite the encouraging efficiencies of Sn-PSCs, they are still yet to surpass 15% and suffer detrimental oxidation of Sn(II) to Sn(IV). Since their first application in 2014, investigations into the properties of Sn-PSCs have contributed to a growing understanding of the mechanisms, both detrimental and complementary to their stability. This review summarizes the evolution of Sn-PSCs, including early developments to the latest state-of-the-art approaches benefitting the stability of devices. The degradation pathways associated with Sn-PSCs are first outlined, followed by describing how composition engineering (A, B site modifications), additive engineering (oxidation prevention), and interface engineering (passivation strategies) can be employed as different avenues to improve the stability of devices. The knowledge about these properties is also not limited to PSCs and also applicable to other types of devices now employing Sn-based perovskite absorber layers. A detailed analysis of the properties and materials chemistry reveals a clear set of design rules for the development of stable Sn-PSCs. Applying the design strategies highlighted in this review will be essential to further improve both the efficiency and stability of Sn-PSCs.

Vapor-Deposited Amino Coupling of Hybrid Perovskite Single Crystals and Silicon Wafers toward Highly Efficient Multiwavelength Photodetection

The complementary integration of perovskite single crystals (PSCs) and silicon-based circuitry provides a feasible way to combine their superiority toward efficient multiwavelength photodetection and imaging readout; however, it suffers from distinct lattice mismatch as well as the ambiguous coupling interface effect. Herein, we develop a vacuum-assisted vapor deposition strategy to realize an ultrauniform aminosiloxane interface-modified silicon wafer, which enables the monolithic epitaxial growth of PSCs with the highest mechanical coupling strength up to 340,000 N m^-2 achieved so far. According to the molecular coupling engineering development with different aminosiloxanes, we achieve a highly efficient multiwavelength-responsive integrated photodetector, possessing specific photodetectivity values of 4.36 × 10¹² jones and 4.55 × 10¹¹ jones within the visible and NIR regions, respectively, as well as the lowest X-ray detection limit of 42.6 nGy_air s^-1. Moreover, a particularly wide -3dB cut-off frequency of 6350 Hz as well as a 120 dB linear dynamic range (LDR) also endows the integrated device with excellent dynamic photodetection capability. This work provides an efficacious approach in the integration technology for PSC-based optoelectronic applications.

Sn-Based Perovskite Halides for Electronic Devices

Because of its less toxicity and electronic structure analogous to that of lead, tin halide perovskite (THP) is currently one of the most favorable candidates as an active layer for optoelectronic and electric devices such as solar cells, photodiodes, and field-effect transistors (FETs). Promising photovoltaics and FETs performances have been recently demonstrated because of their desirable electrical and optical properties. Nevertheless, THP's easy oxidation from Sn²⁺ to Sn⁴⁺ , easy formation of tin vacancy, uncontrollable film morphology and crystallinity, and interface instability severely impede its widespread application. This review paper aims to provide a basic understanding of THP as a semiconductor by highlighting the physical structure, energy band structure, electrical properties, and doping mechanisms. Additionally, the key chemical instability issues of THPs are discussed, which are identified as the potential bottleneck for further device development. Based on the understanding of the THPs properties, the key recent progress of THP-based solar cells and FETs is briefly discussed. To conclude, current challenges and perspective opportunities are highlighted.

Dopamine Hydrochloride-Assisted Synergistic Modulation of Perovskite Crystallization and Sn2+ Oxidation for Efficient and Stable Lead-free Solar Cells

Tin perovskites have received great concern in solar cell research owing to their favorable optoelectronic performance and environmental friendliness. However, due to their poor crystallization and easy oxidation, the performance improvement for tin-based perovskite solar cells (TPSCs) is rather challenging. Herein, reductive 3-hydroxytyramine hydrochloride (DACl) with NH₂·HCl and phenol groups as co-additives with SnF₂ is added into the precursor to modulate perovskite crystallization and inhibit Sn²⁺ oxidation for high-performance TPSCs. The Lewis base group of NH₂ HCl in DACl could bind to perovskite lattices to modulate the crystallization with suppressed defects in the bulk and grain boundary, whereas reductive phenol groups effectively constrain the Sn²⁺ oxidation. Moreover, the undissociated DACl decreases the supersaturated concentration of tin perovskite solution and creates a pre-nucleation site for rapid nucleation to further regulate crystallization. Consequently, the DACl-derived TPSCs achieve a high power-conversion efficiency (PCE) that reaches up to 11%. More impressively, the device remains at 84% of the initial PCE after full-sun illumination in N₂ over 600 h without being encapsulated. This DACl-based synergistic modulation of a lead-free perovskite demonstrates a feasible approach using one molecule with different functional groups to manipulate crystallization, Sn²⁺ oxidation, and defect reparation of tin perovskite films, providing a critical guideline for constructing high-quality perovskites by multifunctional additives with high photovoltaic performance.

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.

Mitigating Voc Loss in Tin Perovskite Solar Cells via Simultaneous Suppression of Bulk and Interface Nonradiative Recombination

Tin-based perovskite solar cells (PSCs) have recently attracted extensive attention as a promising alternative to lead-based counterparts due to their low toxicity and narrow band gap. However, the severe open-circuit voltage (V_oc) loss remains one of the most significant obstacles to further improving photovoltaic performance. Herein, we report an effective approach to reducing the V_oc loss of tin-based PSCs. We find that introducing ethylammonium bromide (EABr) as an additive into the tin perovskite film can effectively reduce defect density both in the tin perovskite film and at the surface as well as optimize the energy level alignment between the perovskite layer and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) transport material, thereby suppressing nonradiative recombination both in the bulk film and at the interface. Furthermore, it is demonstrated that the V_oc loss is gradually mitigated along with increasing storage duration due to the slow passivation effect. As a result, a remarkable V_oc of 0.83 V is achieved in the devices optimized with the EABr additive, which shows a significantly improved power conversion efficiency (PCE) of 10.80% and good stability.