Review of recent progress in chemical stability of perovskite solar cells

Organometal halide perovskite solar cells have demonstrated high conversion efficiency but poor long-term stability against ultraviolet irradiation and water. We show that rapid light-induced free-radical polymerization at ambient temperature produces multifunctional fluorinated photopolymer coatings that confer luminescent and easy-cleaning features on the front side of the devices, while concurrently forming a strongly hydrophobic barrier toward environmental moisture on the back contact side. The luminescent photopolymers re-emit ultraviolet light in the visible range, boosting perovskite solar cells efficiency to nearly 19% under standard illumination. Coated devices reproducibly retain their full functional performance during prolonged operation, even after a series of severe aging tests carried out for more than 6 months.

. This review analyzes current research on perovskite solar cells as an alternative to traditional silicon-based solar cells. The paper discusses various types of solar cell architectures, including different combinations of the main layers, materials for electron and hole transport, as well as the anode, cathode, and conductive substrates. Different approaches to improving the stability and efficiency of these cells are examined through the use of new innovative materials for electron and hole transport layers (ETL and HTL), such as organic and inorganic analogs, as well as tandem and heterostructural elements. A review of the performance and limitations of solar cells with various perovskite materials, including hybrid ones, is also provided. A key issue discussed in the paper is the enhancement of the stability of perovskite solar cells, which can degrade significantly under the influence of moisture, ultraviolet light, and heat. The conclusion is drawn that the use of coatings, additives, and innovative materials contributes to the improvement of the stability of high-efficiency perovskite solar cells. The role of ETL and HTL in enhancing the efficiency and stability of solar cells is also analyzed. The paper emphasizes the importance of research in the field of perovskite solar cells for the development of new efficient, stable cell structures for mass production and commercialization.

Recent review of interfacial engineering for perovskite solar cells: effect of functional groups on the stability and efficiency

Double junction tandem solar cells consisting of two absorbers with designed different band gaps show great advantage in breaking the Shockley-Queisser limit efficiency of single junction solar cell by differential absorption of sunlight in a wider range of wavelengths and reducing the thermal loss of photons. Owing to the advantages of adjustable band gap and low cost of perovskite cells, perovskite/crystalline silicon tandem solar cells have become a research hotspot in photovoltaics. We systematically review the latest research progress of perovskite/crystalline silicon tandem solar cells. Focusing on the structure of perovskite top cells, intermediate interconnection layers and crystalline silicon bottom cells, we summarize the design principles of high-efficiency tandem devices in optical and electrical aspects. We find that the optical and electrical engineering of each layer structure in perovskite/crystalline silicon tandem solar cells goes through the whole process of device preparation. We also summarize the challenges of limiting the further improvement of the efficiency of the perovskite/crystalline silicon tandem solar cells and the corresponding improvement measures, which covers the following respects: 1) Improving the balance between <i>V</i><sub>oc</sub> and <i>J</i><sub>sc</sub> of the broadband perovskite cell through additive engineering and interface engineering; 2) improving the bandgap matching between the electrical layers and reducing the carrier transport barrier through adjusting the work function or conductivity of layers; 3) improving the photocurrent coupling between sub-cells and the photocurrent of tandem solar cells by using light engineering and conformal deposition technology of perovskite cells. At present, there have been many technologies to improve the stability of perovskite solar cells, such as additive engineering and interface engineering, but the problem has hardly been solved. Therefore, improving the stability of broadband gap perovskite solar cells to the level of crystalline silicon solar cells will become an important challenge to limit its large-scale application. In terms of efficiency, the mass production efficiency of perovskite/crystalline silicon tandem solar cells is far lower than that of the laboratory level. One of the reasons is that it is difficult to achieve low-cost and deposition of uniform large area perovskite solar cells. Therefore improving the stability of broadband gap perovskite solar cells and developing low-cost large-area perovskite deposition technology will become extremely critical. Finally we look forward to the next generation of higher efficient low-cost tandem solar cells. We believe that with the increasing demand for higher efficiency photovoltaic devices, the triple junction solar cells based on the perovskite/crystalline silicon stack structure will become the future photovoltaics.

This study aims to investigate the environmental factors that affect the performance and long-term stability of the perovskite solar cells (PSCs). PSCs are based on organometallic halides (perovskites) that act as a light-sensitive compound that produces excitons when placed under the light. However, PSCs have a limited operating lifetime due to the degradation of the perovskite layer. There are many factors like moisture, UV light, and temperature that lead to the degradation of the perovskite layer. The presence of moisture causes an irreversible degradation of the perovskite layer. The performance and the long-term stability of the solar cells were investigated. The structure of the PSC used in this study contains the Transparent Conductive Oxide (TCO), electron transport layer (TiO2), perovskite absorber, hole transport layer, and the conductive metallic silver layer. The solar cells were investigated under various environmental conditions like controlled humidity (30% to 38% RH), high humidity (>50% RH), nitrogen under room temperature of 22°C, and nitrogen under elevated temperature at 80°C. The properties of solar cells studied are the optical absorption of the perovskite absorber, the open-circuit voltage (VOC), short circuit current (ISC), fill factor (FF), and efficiency of the PSCs. The solar cells were stored under light with controlled humidity (30% to 38% RH), high humidity (>50% RH), nitrogen under room temperature of 22°C and elevated temperature of 80°C. Each solar cell under different environments was tested as a function of time. It was found that high humidity, elevated temperature, and presumably the UV part of the white light caused the solar cell to degrade rapidly. It was seen that the nitrogen atmosphere with a room temperature of 22°C had the best environment for storing the perovskite solar cell.

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

Photovoltaics literature survey (no. 149)

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

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

Perovskite solar cells have great potential for high efficiency generation but are subject to the impact of external environmental conditions such as humidity, UV and sun light, temperature, and electric fields. The long-term stability of perovskite solar cells is an important issue for their commercialization. Various studies on the stability of perovskite solar cells are currently being performed; however, the stability related to electric fields is rarely discussed. Here the electrical stability of perovskite solar cells is studied. Ion migration is confirmed using the temperature-dependent dark current decay. Changes in the power conversion efficiency according to the amount of the external bias are measured in the dark, and a significant drop is observed only at an applied voltage greater than 0.8 V. We demonstrate that perovskite solar cells are stable under an electric field up to the operating voltage.

Considering recent highly energy demand of our society, it is obvious that the development of renewable energy sources and high-efficiency devices are very necessary. Solar cells are believed to be a kind of very promising candidate to replace fossil energy to solve the energy crisis problem because solar energy is renewable, free, clean energy. Currently, Perovskite solar cells (PSCs) dominate solar cell research due to their high efficiency, which is reported to achieve an efficiency of ~23%. However, it is still challenging to obtain PSCs with high efficiency and high stability for outdoor applications due to the decomposition of perovskite material under moisture, UV light and thermal conditions. In our work, we used structure engineering including interface layer manipulation and nanoparticle incorporation to improve the stability and efficiency of PSCs. Moisture stability of the devices were improved by hydrophobic layer introduced into PSCs. The hydrophobic layer prevented the moisture penetrating the devices, leading to improved moisture stability. UV light stability was enhanced by light converter, which can convert UV light into visible light. The converted visible light can be absorbed by the perovskite layer to contribute to the photocurrent of the devices. Therefore, both the efficiency and the UV light stability are improved by the UV light converter. Thermal stability of the devices was enhanced by bismuth doping into perovskite film, leading to better crystallinity, uniform morphology, less grain boundaries, and larger grain sizes, which benefited the PSC device performance. To increase the light harvesting, Metallic nanostructures are also introduced into devices to increase the optical path length of the incident light leading to improved light harvesting and increased device efficiency. PSC efficiency was improved to 20% by structure engineering, which is very promising for practical applications. In addition, solar energy storage effect is also obtained by integrating afterglow fluorescence nanomaterials into PSC devices to realize solar cells working in dark conditions.

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.

Organic–inorganic lead halide perovskites have attracted great attention for use in solar cells, because of their efficient solar power conversion, along with compatibility with simple solution processing. To evaluate the operational stability of perovskite solar cells (PSCs), measurements on their current density–voltage (J−V) curves are periodically repeated in most literature studies. However, how the periodic J–V measurements affect the operational stability of PSCs has not been well understood to date. In this study, we found that repeating the J−V measurements, especially applying a voltage higher than the open-circuit voltage of PSCs, under continuous illumination, causes serious ion migration, which lowers the operational stability of PSCs. On the other hand, we observed no decrease in operational stability when the applied voltage is close to or lower than the open-circuit voltage of PSCs during the periodic J−V measurements because of the suppressed ion migration. These findings are important in evaluating the intrinsic operational stability of PSCs.

Perovskite solar cells have recently achieved photo-electric conversion efficiency over 19% showing a promis- ing future for a cost-competitive potovoltaic technology. However, the study of perovskite solar cells' stability didn't catch up with the step of efficiency's process, which is the key issue for commercial application of perovskite solar cells. This re- view discussed the basic issues of the perovskite solar cells' stability under different circumstances, such as oxygen and moisture, UV light, solution process (solvents, solutes, additives), and temperature etc. and summarized how to control the perovskite solar cells' stability under the conditions above. The purpose is to provide a better understanding about perovskite solar cells'stability and the methods to increase the stability of perovskite solar cells under different circumstances. Keywords perovskite solar cells; high efficiency; chemical stability; circumstances; control