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

Synergistic Interfacial Dipole and π-Conjugation Effects Enable Efficient Tin Perovskite Solar Cells

Tin perovskites are considered promising candidates for realizing high-performance, lead-free perovskite solar cells (PSCs). Despite prominent progress made through bulk optimization, unsatisfactory interfaces between tin perovskite and charge transport layers are critical obstacles to boosting device performance. Herein, we address this issue by introducing piperazine dihydroiodide (PDI) and ferrocene (Fc) at the interface of tin perovskite/C60 to synergistically improve the interfacial charge transport. Specifically, PD+ interacts with formamidinium ions (FA+) to form an interfacial dipole, and Fc establishes π-π conjugation with C60. These effects significantly improve electron extraction at the tin perovskite/C60 interface and reduce energy losses. As a result, the efficiency of tin PSCs is remarkably improved from 10.62% to 13.65%, accompanied by enhanced stability. This work highlights the importance of interfacial modulation in tin PSCs toward realizing efficient and eco-friendly perovskite photovoltaics.

Multifunctional small molecule interface management for efficient planar perovskite solar cells

Establishing an optimal configuration for the electron transport layer (ETL) and a compliant perovskite interface is pivotal in advancing the creation of high-performance, hysteresis-free, and resilient perovskite solar cells (PSCs). Amongst various strategies, interface engineering emerges as a highly feasible and potent means to alleviate interfacial non-radiative recombinations, issues typically rooted in defects, tensile stresses, and energy level discrepancies at the interface. Our investigation solidifies the efficacy of incorporating Imidazolium Salt (NOI:1N-3-acetic acid-imidazole) within the SnO2/perovskite interface as a strategic intervention for remodeling this vital frontier. The integration of NOI fosters a synergistic interface, seamlessly bridging the perovskite with the SnO2 ETL, effectively mitigating tensile strains and passivating underlying interface defects. Implementation of the NOI-based treatment regimen has notably propelled device performance, evidenced by a PCE escalation from 21.5% to 23.3%, coupled with a marked increase in open-circuit voltage (VOC) from 1.15 V to 1.18 V. Consequently, this methodology presents a concise yet powerful pathway for augmenting PSCs' operational excellence.

Enhancing Charge Collection of Tin-Based Perovskite Solar Cells by Optimizing the Buried Interface with a Multifunctional Self-Assembled Monolayer

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transport material in inverted tin-based perovskite solar cells (Sn-PSCs). However, the efficiency and stability of these Sn-PSCs that utilize PEDOT:PSS are unsatisfactory, partly due to concerns about their mismatched work functions, hydrophobicity, and chemical interactions. Here, we introduce a self-assembled monolayer (SAM), (2-(7H-dibenzo[c,g]carbazol-7-yl)ethyl) phosphonic acid (2PADCB) as a multifunctional buffer molecule at the buried PEDOT:PSS/Sn perovskite interface. The phosphate group in the 2PADCB molecule reacts with the sulfur atom on the thiophene ring in PEDOT:PSS. This reaction process effectively anchors the SAM molecule firmly to the surface of PEDOT:PSS. Additionally, it reduces the binding sites between PEDOT and PSS, alleviating the acidification of the PEDOT:PSS surface and the poor conductivity caused by excessive PSS. Furthermore, the presence of two additional benzene rings in the 2PADCB molecule terminal group increases the electron density around Sn2+, thereby inhibiting its oxidation. Additionally, the hydrophobic characteristics of the 2PADCB molecule mitigate moisture infiltration from PEDOT:PSS, thereby protecting the degradation of Sn perovskite. Consequently, the Sn-PSCs based on the PEDOT:PSS/2PADCB film achieve a champion efficiency of 14.7%, higher than that of their pristine counterpart (12.5%). Moreover, the 2PADCB molecule improves the stability of the device by maintaining 90% of its initial efficiency after 160 h under 1 Sun illumination. Such enhancement in efficiency and stability is mainly attributed to the improved interface quality with the 2PADCB molecule, leading to better carrier transport and suppressed charge recombination at the buried PEDOT:PSS/Sn perovskite interface. Our work suggests that introducing the 2PADCB molecule at the PEDOT:PSS/perovskite interface is a promising method for efficient and stable Sn-PSCs.

In Situ Polymerization Strategy for Improving the Stability of Sn-Based Perovskite Solar Cells

Sn-based perovskite solar cells (Sn-PSCs) have received increasing attention due to their nontoxicity and potentially high efficiency. However, the poor stability of Sn2+ ions remains a major problem in achieving stable and efficient Sn-PSCs. Herein, an in situ polymerization strategy using allyl thiourea and ethylene glycol dimethacrylate as cross-linking agents in the Sn-based perovskite precursor is proposed to improve the device performance of Sn-PSCs. The C═S and N-H bonds of the cross-linkers are able to coordinate with SnI2 and inhibit the oxidation of Sn2+, thereby reducing defect density and improving the stability of Sn-based perovskite films. The high quality of the perovskite film induced by the in situ polymerization strategy delivers an improved power conversion efficiency (PCE) from 7.50 to 9.22%. More importantly, the unpackaged device with cross-linkers maintained more than 70% of the initial PCE after 150 h of AM 1.5G light soaking in a nitrogen atmosphere and 80% of the initial PCE after 1800 h in dark conditions. This work demonstrates that the in situ polymerization strategy is an effective method to enhance the stability of Sn-based perovskite films and devices.

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.

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.

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.

Dendrimer Modification Strategy Based on the Understanding of the Photovoltaic Mechanism of a Perovskite Device under Full Sun and Indoor Light

The wide-band-gap inorganic CsPbI₂Br perovskite material provides a highly matched absorption range with the indoor light spectrum and is expected to be used in the fabrication of highly efficient indoor photovoltaic cells (IPVs) and self-powered low-power Internet of Things (IoT) sensors. However, the defects that cause nonradiative recombination and ion migration are assumed to form leakage loss channels, resulting in a severe impact on the open-circuit voltage (V_OC) and the fill factor (FF) of IPVs. Herein, we introduce poly(amidoamine) (PAMAM) dendrimers with multiple passivation sites to fully repair the leakage channels in the devices, taking into account the characteristics of IPVs that are extremely sensitive to nonradiative recombination and shunt resistance. The as-optimized IPVs demonstrate a promising PCE of 35.71% under a fluorescent light source (1000 lux), with V_OC increased from 0.99 to 1.06 V and FF improved from 75.21 to 84.39%. The present work provides insight into the photovoltaic mechanism of perovskites under full sun and indoor light, which provides guidance for perovskite photovoltaic technology with industrialization prospects.

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.

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.

Recent Advancements in Tin Halide Perovskite-Based Solar Cells and Thermoelectric Devices

The excellent optoelectronic properties of tin halide perovskites (Sn-PVKs) have made them a promising candidate for replacing toxic Pb counterparts. Concurrently, their enormous potential in photon harvesting and thermoelectricity applications has attracted increasing attention. The optoelectronic properties of Sn-PVKs are governed by the flexible nature of SnI₆ octahedra, and they exhibit extremely low thermal conductivity. Due to these diverse applications, this review first analyzes the structural properties, optoelectronic properties, defect physics, and thermoelectric properties of Sn-PVKs. Then, recent techniques developed to solve limitations with Sn-PVK-based devices to improve their photoelectric and thermoelectric performance are discussed in detail. Finally, the challenges and prospects for further development of Sn-PVK-based devices are discussed.