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Lead halide perovskites are renowned for their remarkable photophysical properties, making them prime candidates for advanced optoelectronic devices. However, the toxicity of lead is motivating research of lead-free perovskites using environmentally friendly alternatives for safer photovoltaic applications. Here, we investigate cesium antimony iodide (Cs3Sb2I9) perovskite-inspired material (PIM) as a lead-free option. A key limitation in the solar cell performance of this PIM is trap-assisted nonradiative recombination at the perovskite/hole transporting layer interface. We report an effective surface passivation strategy using dimethyl phenethyl sulfonium iodide (DMPESI). This approach significantly reduces surface defect density, minimizes nonradiative recombination, and enhances charge carrier transport. The optimized DMPESI-modified perovskite films achieved a power conversion efficiency of 2.63%, with an open-circuit voltage of 0.80 V, a short-circuit current density of 4.57 mA cm(-2), and a high fill factor of 0.72, representing one of the highest device performances reported to date for Cs3Sb2I9. Furthermore, the passivated devices demonstrated improved operational stability. Photocurrent spectra suggest that short electron diffusion length in Cs3Sb2I9 is another limiting factor for these devices. These findings offer valuable insights into surface engineering techniques that could enhance the performance of lead-free photovoltaic devices, suggesting that antimony-based Cs3Sb2I9 holds substantial potential for future environmentally friendly photovoltaic applications.

Low-temperature-processed carbon-based perovskite solar cells (C-PSCs) are a potential candidate for industrial development, due to their low cost, high stability, and easy preparation methods. However, their power conversion efficiencies still lag behind that of metal-contact-based PSCs, due to poor compatibility of the carbon electrode with the underlying layers. Here, we introduce a doping-free poly(3-hexylthiophene) (P3HT) hole-transport layer deposited from chloroform to improve solar cell performance of PSCs that are prepared in ambient air. The resulting P3HT films have a lower roughness and a higher conductivity. A champion device with power conversion efficiency of 19.4% was obtained with negligible hysteresis and a remarkably enhanced fill factor (FF) of 80.2%. Unencapsulated devices maintained 70% of initial efficiency value after 350 hr under thermal stress at 85 degrees C in dark and ambient air.

Ion migration and lead toxicity present significant challenges to commercializing lead halide perovskites (LHPs) based solar cells, particularly the presence of lead obstructs their use in indoor photovoltaics (IPVs). Recently, antimony-based perovskite-inspired materials (PIMs) have emerged as promising alternatives for IPVs. However, the detailed understanding of the ion migration pathways in PIMs and their impact on device kinetics and stability remain largely unexplored. The systematic study, comparing ionic conduction in PIMs with the well-studied LHPs, provides broader mechanistic insights into ionic conduction. This comparison highlights the correlation between ionic conduction, anomalous device behavior, and operational stability. The slower ionic conduction in PIMs, resulting from the high formation energy of halide defects, leads to weaker polarization at the interface and, consequently, higher operational stability. The higher non-radiative recombination rate, coupled with lower ionic mobility, leads to a pronounced negative capacitance after a specific applied bias. Furthermore, first-principles calculations explore potential ion migration pathways and their minimum activation energies in PIMs. The work therefore provides valuable insights into ion dynamics in both PIMs and LHPs, with important implications for designing novel materials and advancing future applications.

Perovskite solar cells (PSCs) hold significant promise as the next-generation materials in photovoltaic markets, owing to their ability to achieve impressive power conversion efficiencies, streamlined fabrication processes, cost-effective manufacturing, and numerous other advantages. The utilization of self-assembled monolayer (SAM) molecules has proven to be a significant success in enhancing device efficiency and extending device stability. This review highlights the dual use of SAM molecules in the realm of PSCs, which can not only serve as charge transport materials but also act as interfacial modulators. These research endeavors encompass a wide range of applications for various SAM molecules in both n-i-p and p-i-n structured PSCs, providing a deep insight into the underlying mechanisms. Furthermore, this review proposes current research challenges for future investigations into SAM materials. This timely and thorough review seeks to provide direction and inspiration for current research efforts dedicated to the ongoing incorporation of SAMs in the field of perovskite photovoltaics. Self-assembled monolayer (SAM) molecules are extensively employed in perovskite solar cells, serving both as charge transport materials and interfacial modulators. These molecules play a crucial role in adjusting surface energy levels, reducing interfacial trap defects, and enhancing perovskite crystallization quality, thereby leading to improved performance and stability of perovskite solar cells. image

The efficient production of uniform, high-quality transport layers beneath the light-absorbing layer is crucial for the performance and scalability of perovskite solar cells (PSCs). This study investigates the incorporation of potassium fluoride (KF) into tin dioxide (SnO2) nanoparticle solutions to enhance the properties of the electron transport layer (ETL) in PSCs. By introducing KF, we observed a significant reduction in SnO2 particle size and improved zeta potential, resulting in a more uniform ETL. Experimental analysis demonstrated that optimal KF concentrations in SnO₂ nanoparticles improved coverage and uniformity on substrates, as confirmed by surface SEM and AFM measurement. Such improvement in ETL morphology reduced charge recombination and increased charge carrier mobility of PSCs. Specifically, PSCs with 0.02 M of KF addition showed increased power conversion efficiencies (PCE), up to 24.3%. Furthermore, large-area PSC modules with a 25 cm2 aperture area exhibited an average PCE enhancement up to 18.0% due to superior ETL uniformity. Additionally, KF addition also aided the stability enhancement, maintaining 90% of their initial efficiency after 250 hours under 60 ± 5% relative humidity. Our findings underscore the importance of ETL uniformity and provide insights into the role of KF doping in advancing PSC performance, paving the way for more efficient and scalable solar energy solutions.

Reversible optical property changes in lead-free perovskites have recently received great interest due to their potential applications in smart windows, sensors, data encryption, and various on-demand devices. However, it is challenging to achieve remarkable color changes in their thin films. Here, methylamine gas (CH₃NH₂, MA⁰) induced switchable optical bleaching of bismuth (Bi)-based perovskite films is demonstrated for the first time. By exposure to an MA⁰ atmosphere, the color of Cs₂AgBiBr₆ (CABB) films changes from yellow to transparent, and the color of Cs₃Bi₂I₉ (CBI) films changes from dark red to transparent. More interestingly, the underlying reason is found to be the interactions between MA⁰ and Bi³⁺ with the formation of an amorphous liquefied transparent intermediate phase, which is different from that of lead-based perovskite systems. Moreover, the generality of this approach is demonstrated with other amine gases, including ethylamine (C₂H₅NH₂, EA⁰) and butylamine (CH₃(CH₂)₃NH₂, BA⁰), and another compound, Cs₃Sb₂I₉, by observing a similar reversible optical bleaching phenomenon. The potential for the application of CABB and CBI films in switchable smart windows is investigated. This study provides valuable insights into the interactions between amine gases and lead-free perovskites, opening up new possibilities for high-efficiency optoelectronic and stimuli-responsive applications of these emerging Bi-based materials.

Efficient photosensitizers are crucial for advancing solar energy conversion and storage technologies. In this study, we designed and synthesized a novel organic dye, denoted as YB6, for p-type dye-sensitized solar cells (p-DSCs) and photoelectrochemical H₂O₂ production. YB6 features an extended conjugated pi-bridge derived from indacenodithieno[3,2-b]thiophene and exhibits notable advantages: a two-fold higher molar extinction coefficient at its main absorption peak and a broader absorption as compared to the PB6 dye. In p-type dye-sensitized NiO photoelectrochemical cells, the YB6-based device demonstrated superior performance as compared to the PB6-based device. It delivered nearly a 50 % higher H₂O₂ production over 5 hours. Furthermore, when fabricated into p-DSCs, the YB6-based device exhibited a 33 % higher power conversion efficiency. This enhancement is caused by suppressed charge recombination from the dye structure, which in turn may be traced to a larger thermodynamic up-hill process for recombination losses in the YB6-based system.

Perovskite solar cells (PSCs) have attracted significant attention for their utility in next-generation energy production technology due to their rapidly increasing power conversion efficiencies (PCEs), which have recently reached levels comparable to those of commercially successful Si solar cells. The simplicity and low cost of the perovskite solution processability have further heightened their commercial viability. However, the use of N,N-dimethylformamide (DMF)─a volatile toxic solvent─in this process is considered to be a major issue that not only poses significant challenges at the lab scale but also can potentially lead to serious human and environmental damage if introduced into production lines upon being commercialized. The present study aims to address the toxicity problem by classifying solvents into green and toxic categories and using only green solvents in the solution process to create high-efficiency PSCs. A specific challenge encountered in this process was the solubility issue of perovskite materials in green solvents, which led to the creation of perovskite films with inferior optical and electrical properties. This issue was resolved by ionizing perovskite materials with the addition of organic halide materials, ultimately enabling the fabrication of PSCs with PCEs reaching up to 20.6%. The green PCE metric of all-layer green solvent PSC is as high as 4.54, exceeding that of all the green solvent-based PSCs, thereby showing that this process achieves high efficiency while addressing relevant environmental and health impacts.

Lead halide perovskite photovoltaics have shown an impressive efficiency increase over the past decade. Making this technology industrially viable requires precise optimization of every single deposition step. Here we used slot-die coating, a promising scalable deposition technique to enable large scale deposition. We demonstrate the challenges in developing high-quality slot-die coated tin oxide (SnO₂) films, suited as electron selective layers in perovskite solar cells. We studied the film quality of two commercially available colloidal SnO₂ dispersions by controlling pump rate, coating speed and temperature of the indium tin oxide substrates (ITO). The water-based dispersion was more difficult to control, but resulted in better perovskite solar cell performance than the butanol-based dispersion. Hysteresis in J–V curves from the water-based tin oxide dispersion was reduced by potassium fluoride addition. A maximum power conversion efficiency of 17.5% was achieved for MAPbI₃-based solar cells by careful optimization of the deposition parameters.

Organic hole-transporting materials (HTMs) are of importance in the progress of new-generation photovoltaics, notably in perovskite solar cells (PSCs), solid-state dye-sensitized solar cells (sDSCs), and organic solar cells (OSCs). These materials play a vital role in hole collection and transportation, significantly impacting the power conversion efficiency (PCE) and overall stability of photovoltaic devices. The emergence of spiro(fluorene-9,9 '-xanthene) (SFX) as a novel building block for organic HTMs has gained considerable attention in the field of photovoltaics. Its facile one-pot synthetic approach, straightforward purification, and physiochemical properties over the prototype HTM spiro-OMeTAD have positioned SFX as a highly attractive alternative. In this Account, we present a comprehensive and in-depth summary of our research work, focusing on the advancements in SFX-based organic HTMs in photovoltaic devices with a particular emphasis on PSCs and sDSCs. Several key objectives of our research have been focused on exploring strategies to improve the properties of SFX-based HTMs. (i) One of the critical aspects we have addressed is the improvement of film quality. By carefully designing the molecular structure and employing suitable synthetic approaches, we have achieved HTMs with excellent film-forming ability, resulting in uniform and smooth films over large areas. This achievement is pivotal in ensuring the reproducibility and efficiency of photovoltaic devices. Furthermore, (ii) our investigations have led to an improvement in hole mobility within the HTMs. Through molecular engineering, such as increasing the molecular conjugation and introducing multiple SFX units, we have demonstrated enhanced charge-carrier mobility. This advancement plays a crucial role in minimizing charge recombination losses and improving the overall device efficiency. Additionally, (iii) we have explored the concept of defect passivation in SFX-based HTMs. By incorporating Lewis base structures, such as pyridine groups, we have successfully coordinated to Pb2+ in the perovskite layer, resulting in a passivation of surface defects. This defect passivation contributes to better stability and enhanced device performance. Throughout our review, we highlighted the potential and opportunities achieved through these steps. The combination of enhanced film quality, improved hole mobility, and defect passivation resulted in remarkable photovoltaic performance. Our findings have demonstrated promising short-circuit current densities, open-circuit voltages, fill factors, and PCEs, with some HTMs even outperforming the widely used spiro-OMeTAD. We believe that this review will not only provide a better understanding of SFX-based HTMs but also open new avenues for enhancing the performance of organic HTMs in photovoltaic and other organic electronic devices. By providing unique perspectives and exploring different strategies, we aim to inspire ongoing advancements in photovoltaic technologies and organic electronics. Meanwhile, the success of SFX-based HTMs in improving photovoltaic device performance holds great promise for the continued development of efficient and stable photovoltaic devices in the years to come.