An efficient guanidinium isothiocyanate additive for improving the photovoltaic performances and thermal stability of perovskite solar cells

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Two-dimensional Bi2OS2 doping improves the performance and stability of perovskite solar cells

ABX<sub>3</sub> crystalline perovskite material has many advantages: good photoelectric absorption property, high charge carrier mobility, good film formation, long charge carrier lifetime, and easy bandgap adjustment for absorption layer of perovskite solar cells. As a result, the power conversion efficiency (PCE) of the organic-inorganic halide perovskite solar cells (PSCs) has taken a tremendous step forward, from 3.9% in 2009 to a recently reported value over 25.5%. Thus, it shows great potential to compete with traditional silicon solar cells. However, PSCs preparing conditions are harsh and susceptible to environmental influences, thus leading to instability. Therefore, it is essential to prepare high-performance and stable PSCs in an air environment. This study aims to use the ion doping method to improve the performance and stability of PSCs and analyze the mechanism. This work focuses on enhancing PSCs efficiency and stability by performing FA<sup>+</sup> and Cl<sup>–</sup> doping experiments on MAPbI<sub>3</sub> films in air. The results show that a single Cl<sup>–</sup>-doping increases the carrier diffusion length, reducing the recombination of electrons and holes, and inducing the perovskite intermediate hydrate (CH<sub>3</sub>NH<sub>3</sub>)<sub>4</sub>PbI<sub>6</sub>·2H<sub>2</sub>O to form, promoting the crystallization of the thin film, and improving the device performance. On the other hand, a single FA<sup>+</sup>-doping will reduce the bandgap of perovskite and increase the short-circuit current density (<i>J</i><sub>SC</sub>) of the device, and FA<sup>+</sup> is susceptible to the influence of water vapor to induce a yellow <i>δ</i>-FAPbI<sub>3</sub> perovskite film to form, which leads the device performance to degrade. However, the prepared co-doping Cl<sup>–</sup>, FA<sup>+</sup> significantly improves overall PSCs device performance, yielding the highest PCE of 17.29%, and showing excellent stability by maintaining over 80% of the original PCE without any encapsulation after 1000-hour storage in ambient air.

The low stability of perovskite solar cells is the limiting factor for their commercialization, which is largely affected by defects originating from crystallographic distortions and interface formation in solution-processed lead halide perovskite thin films. Herein, urea and thiourea small molecules are used as dopants to synergistically increase the power conversion efficiency (PCE) and stability of the perovskite solar cells by regulating the morphology and crystallinity of the perovskite thin films. X-ray diffraction, atomic force microscopy, Fourier-transform infrared spectroscopy, transmittance spectra, day-dependent photoluminescence (PL), and Raman scattering spectra are used to briefly compare the crystal growth and defect passivation mechanisms of urea and thiourea small molecules. The PCE of thiourea-doped perovskite solar cells gradually increases as a function of storage duration, from 12.12 ± 0.15% to 18.38 ± 89% in 40 days. Day-dependent PL and Raman scattering spectra reveal that the crystallinity of the thiourea-doped perovskite thin film improves over time, resulting in slow passivation from thiourea small molecules and consequently an improvement in device performance.

Improving the efficiency and stability of perovskite solar cell through tetrabutylammonium hexafluorophosphate post-treatment assisted top surface defect passivation

High photoelectric conversion efficiency and stability of carbon-based perovskite solar cells based on sandwich-structured electronic layers

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

A compromise between high power conversion efficiency and long-term stability of hybrid organic-inorganic metal halide perovskite solar cells is necessary for their outdoor photovoltaic application and commercialization. Herein, a method to improve the stability of perovskite solar cells under water and moisture exposure consisting of the encapsulation of the cell with an ultrathin plasma polymer is reported. The deposition of the polymer is carried out at room temperature by the remote plasma vacuum deposition of adamantane powder. This encapsulation method does not affect the photovoltaic performance of the tested devices and is virtually compatible with any device configuration independent of the chemical composition. After 30 days under ambient conditions with a relative humidity (RH) in the range of 35-60%, the absorbance of encapsulated perovskite films remains practically unaltered. The deterioration in the photovoltaic performance of the corresponding encapsulated devices also becomes significantly delayed with respect to devices without encapsulation when vented continuously with very humid air (RH > 85%). More impressively, when encapsulated solar devices were immersed in liquid water, the photovoltaic performance was not affected at least within the first 60 s. In fact, it has been possible to measure the power conversion efficiency of encapsulated devices under operation in water. The proposed method opens up a new promising strategy to develop stable photovoltaic and photocatalytic perovskite devices.

Perovskite solar cells (PSCs) are solar cells with the light-absorbing layers made of perovskite materials. Perovskite materials are a class of materials that possess a distinct crystal structure that resembles that of mineral perovskite. PSCs have received significant attention in recent years due to their remarkable power conversion efficiency, uncomplicated manufacturing process, cost-effectiveness, and potential for large-scale production. However, PSCs face challenges, particularly in terms of stability and durability. Perovskite materials are known for their sensitivity to moisture and oxygen. This can lead to reduction in their performance over time. Researchers are actively engaged in enhancing the stability of perovskite solar cells via various approaches, including interface manipulation and the incorporation of stabilizing agents. Endeavors are underway to surmount obstacles such as trap-assisted nonradiative recombination and inadequate ambient stability. Through further progress in formulation, composition, and interfacial optimization, PSCs hold promise in nearing their theoretical efficiency threshold of 31% and emerging as a feasible candidate for commercial and industrial applications. The power conversion efficiency (PCE) of perovskite solar cells have been steadily increasing over the years while the stability has not advanced much. Currently, the PCE and stability of single-junction perovskite solar cells have reached 27.0% and 10,000 h, respectively. Perovskite Tandem and Hybrid Tandem solar cells have achieved higher efficiencies of 30.1% and 36.1%, respectively. Efforts are still ongoing to explore different approaches to further increase the efficiency, improve stability under real working conditions, and employ lead-free perovskite materials.

The power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) are significantly reduced by defect-induced charge non-radiative recombination. Also, unexpected residual strain in perovskite films leads to an unfavorable impact on the stability and efficiency of PSCs, notably flexible PSCs (f-PSCs). Considering these problems, a thorough and effective strategy is proposed by incorporating phytic acid (PA) into SnO2 as an electron transport layer (ETL). With the addition of PA, the Sn inherent dangling bonds are passivated effectively and thus enhance the conductivity and electron mobility of SnO2 ETL. Meanwhile, the crystallization quality of perovskite is increased largely. Therefore, the interface/bulk defects are reduced. Besides, the residual strain of perovskite film is significantly reduced and the energy level alignment at the SnO2/perovskite interface becomes more matched. As a result, the champion f-PSC obtains a PCE of 21.08% and rigid PSC obtains a PCE of 21.82%, obviously surpassing the PCE of 18.82% and 19.66% of the corresponding control devices. Notably, the optimized f-PSCs exhibit outstanding mechanical durability, after 5000 cycles of bending with a 5mm bending radius, the SnO2-PA-based device preserves 80% of the initial PCE, while the SnO2-based device only remains 49% of the initial value.

Organometal trihalide perovskites (OTPs) are emerging as very promising photovoltaic materials because the power conversion efficiency (PCE) of OTP solar cells quickly rises and now rivals with that of single crystal silicon solar cells after only five-years research. Their prospects to replace silicon photovoltaics to reduce the cost of renewable clean energy are boosted by the low-temperature solution processing as well as the very low-cost raw materials and relative insensitivity to defects. The flexibility, semitransparency, and vivid colors of perovskite solar cells are attractive for niche applications such as built-in photovoltaics and portable lightweight chargers. However, the low stability of current hybrid perovskite solar cells remains a serious issue to be solved before their broad application. Among all those factors that affect the stability of perovskite solar cells, ion migration in OTPs may be intrinsic and cannot be taken away by device encapsulation. The presence of ion migration has received broad attention after the report of photocurrent hysteresis in OTP based solar cells. As suggested by much direct and indirect experimental evidence, the ion migration is speculated to be the origin or an important contributing factor for many observed unusual phenomenon in OTP materials and devices, such as current-voltage hysteresis, switchable photovoltaic effect, giant dielectric constant, diminished transistor behavior at room temperature, photoinduced phase separation, photoinduced self-poling effect, and electrical-field driven reversible conversion between lead iodide (PbI2) and methylammonium lead triiodide (MAPbI3). Undoubtedly thorough insight into the ion-migration mechanism is highly desired for the development of OTP based devices to improve intrinsic stability in the dark and under illumination. In this Account, we critically review the recent progress in understanding the fundamental science on ion migration in OTP based solar cells. We look into both theoretical and experiment advances in answering these basic questions: Does ion migration occur and cause the photocurrent hysteresis in perovskite solar cells? What are the migrating ion species? How do ions migrate? How does ion migration impact the device efficiency and stability? How can ion migration be mitigated or eliminated? We also raise some questions that need to be understood and addressed in the future.

The rapid rise of power conversion efficiency (PCE) of low cost organometal halide perovskite solar cells suggests that these cells are a promising alternative to conventional photovoltaic technology. However, anomalous hysteresis and unsatisfactory stability hinder the industrialization of perovskite solar cells. Interface engineering is of importance for the fabrication of highly stable and hysteresis free perovskite solar cells. Here we report that a surface modification of the widely used TiO2 compact layer can give insight into interface interaction in perovskite solar cells. A highest PCE of 18.5% is obtained using anatase TiO2, but the device is not stable and degrades rapidly. With an amorphous TiO2 compact layer, the devices show a prolonged lifetime but a lower PCE and more pronounced hysteresis. To achieve a high PCE and long lifetime simultaneously, an insulating polymer interface layer is deposited on top of TiO2. Three polymers, each with a different functional group (hydroxyl, amino, or aromatic group), are investigated to further understand the relation of interface structure and device PCE as well as stability. We show that it is necessary to consider not only the band alignment at the interface, but also interface chemical interactions between the thin interface layer and the perovskite film. The hydroxyl and amino groups interact with CH3NH3PbI3 leading to poor PCEs. In contrast, deposition of a thin layer of polymer consisting of an aromatic group to prevent the direct contact of TiO2 and CH3NH3PbI3 can significantly enhance the device stability, while the same time maintaining a high PCE. The fact that a polymer interface layer on top of TiO2 can enhance device stability, strongly suggests that the interface interaction between TiO2 and CH3NH3PbI3 plays a crucial role. Our work highlights the importance of interface structure and paves the way for further optimization of PCEs and stability of perovskite solar cells.

Surface passivation has demonstrated to be an effective strategy to improve the power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). Passivation treatment can effectively reduce the density of defect states at the surface and grain boundaries of perovskite films. Herein, a passivation agent of 2-amino-5-(trifluoromethyl)pyridine (5-TFMAP) with bidentate groups is applied to passivate perovskite CH3NH3PbI3 films for the first time. Two types of electron-rich nitrogen atoms from both the pyridine ring and the amino group provide strong interaction with the under-coordinated Pb2+. Additionally, the trifluoromethyl group offers a hydrophobic property and improves moisture stability of the as-fabricated PSCs. It is found that the 5-TFMAP passivation layer can effectively reduce the defect states, promote better carrier transport, and suppress non-radiation recombination of the perovskite films. The best PCE of carbon-based PSCs passivated by the 5-TFMAP agent achieves a high efficiency of 14.96% compared with that of 11.90% for the control PSCs. Moreover, the long-term stability of PSCs with the 5-TFMAP passivation treatment is greatly improved, and its PCE can maintain 80% of its original PCE after being stored for 1200 h with a relative humidity of around 35% at room temperature.

Organic-inorganic hybrid perovskite solar cells have attracted much attention due to their high power conversion efficiency (>25%) and low-cost fabrication. Yet, improvements are still needed for more stable and higher-performing solar cells. In this work, a series of TiO2 nanocolumn photonic structures have been intentionally fabricated on half of the compact TiO2-coated fluorine-doped tin oxide substrate by glancing angle deposition with magnetron sputtering, a method particularly suitable for industrial applications due to its high reliability and reduced cost when coating large areas. These vertically aligned nanocolumn arrays were then applied as the electron transport layer into triple-cation lead halide perovskite solar cells based on Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3. By comparison to solar cells built onto the same substrate without nanocolumns, the use of TiO2 nanocolumns can significantly enhance the power conversion efficiency of the perovskite solar cells by 7% and prolong their shelf life. Here, detailed characterizations on the morphology and the spectroscopic aspects of the nanocolumns, their near-field and far-field optical properties, solar cells characteristics, as well as the charge transport properties provide mechanistic insights on how one-dimensional TiO2 nanocolumns affect the performance of perovskite halide solar cells in terms of charge transport, light harvesting, and stability, knowledge necessary for the future design of higher-performing and more stable perovskite solar cells.

Improving stability of perovskite solar cells using BMIMBF4/IPA as green mixed anti-solvent