Perovskite Solar Cells: A Review of the Recent Advances

Tailoring Interface via Tuning the Phase and Morphology of TiO2 for Efficient Mesoporous Perovskite Solar Cells

The efficiency of mesoporous perovskite solar cells (mp-PSCs) is significantly influenced by favorable charge transport properties across their various interfaces. The interfaces involving compact-TiO2, mesoporous electron transport layer (ETL), and perovskite layer are particularly vital for high-performing devices. Our study presents a combined experimental and computational approach, specifically employing density functional theory, to explore the impact of mesoporous-ETL/perovskite interface properties on carrier transport. These properties are examined in relation to the phases and morphologies of the mesoporous layer. Different phases of TiO2, including anatase, rutile, and brookite, and various morphologies such as nanocubes, nanorods, and disks/clusters, were synthesized using a simple hydrothermal synthesis route. They constitute the mesoporous layer, and Cs0.05FA0.84MA0.14PbI2.55Br0.45 is used as the perovskite absorber in mp-PSCs. The performance of the resulting mesoporous-TiO2 (mp-TiO2) device was investigated in relation to the different phases and morphologies of mp-TiO2. The mp-PSCs with the anatase phase as the mesoporous ETL exhibited the highest device parameters, including power conversion efficiency of 19.15%, short-circuit current density of 22.55 mA/cm2, fill factor of 76.50%, and open-circuit voltage of 1.11 V. The superior performance of the anatase structure is attributed to its promising band edge alignment, which results from a small negative conduction band offset compared to other phases, thereby enhancing carrier transport. This study underscores the potential of interface optimization to improve device performance. By investigating the device performance across different phases and morphologies of the mp-TiO2 layer, we can pave the way for the design of next-generation energy devices.

Performance of Low-Dimensional Solid Room-Temperature Photodetectors-Critical View

In the last twenty years, nanofabrication progress has allowed for the emergence of a new photodetector family, generally called low-dimensional solids (LDSs), among which the most important are two-dimensional (2D) materials, perovskites, and nanowires/quantum dots. They operate in a wide wavelength range from ultraviolet to far-infrared. Current research indicates remarkable advances in increasing the performance of this new generation of photodetectors. The published performance at room temperature is even better than reported for typical photodetectors. Several articles demonstrate detectivity outperforming physical boundaries driven by background radiation and signal fluctuations. This study attempts to explain these peculiarities. In order to achieve this goal, we first clarify the fundamental differences in the photoelectric effects of the new generation of photodetectors compared to the standard designs dominating the commercial market. Photodetectors made of 2D transition metal dichalcogenides (TMDs), quantum dots, topological insulators, and perovskites are mainly considered. Their performance is compared with the fundamental limits estimated by the signal fluctuation limit (in the ultraviolet region) and the background radiation limit (in the infrared region). In the latter case, Law 19 dedicated to HgCdTe photodiodes is used as a standard reference benchmark. The causes for the performance overestimate of the different types of LDS detectors are also explained. Finally, an attempt is made to determine their place in the global market in the long term.

The Perovskite Optoelectronic Devices - A Look at the Future

The perovskite materials are broadly incorporated into optoelectronic devices due to a number of advantages. Their rapid technological progress is related to the relatively simple fabrication process, low production cost and high efficiency. Significant improvement is made in the light emitting, detection performance and device design especially operating in the visible and near-infrared regions. This review presents the status and possible future development of the perovskite devices such as solar cells, photodetectors, and light-emitting diodes. The fundamental properties of perovskite materials related to their effective device applications are summarized. Since the development of the perovskite technology is mainly driven by the revolutionary evolution of the semiconductor perovskite solar cell as a robust candidate for next-generation solar energy harvesting, this topic is considered first. The device engineering of various perovskite photodetector structures, including perovskite quantum dot photodetectors, is then discussed in detail. Their performance is compared with the current commercial photodetectors available on the global market together with their challenges. Finally, the considerable progress in the fabrication of the perovskite light-emitting diodes with external quantum efficiency exceeding 20% is presented. The paper is completed in an attempt to determine the development of perovskite optoelectronic devices in the future.

Anti-solvent materials enhanced structural and optical properties on ambiently fabricated perovskite thin films

Perovskite solar cells (PSCs) hold potential for low-cost, high-efficiency solar energy, but their sensitivity to moisture limits practical application. Current fabrication requires controlled environments, limiting mass production. Researchers aim to develop stable PSCs with longer lifetimes under ambient conditions. In this research work, we investigated the stability of perovskite films and solar cells fabricated and annealed in natural air using four different anti-solvents: toluene, ethyl acetate, diethyl ether, and chlorobenzene. Films (about 300 nm thick) were deposited via single-step spin-coating and subjected to ambient air-atmosphere for up to 30 days. We monitored changes in crystallinity, electrical properties, and optics over time. Results showed a gradual degradation in the films' crystallinity, morphology, and electro-optical properties. Notably, films made with ethyl acetate exhibited superior stability compared to other solvents. These findings contribute to advancing stable and high-performance PSCs manufactured under normal ambient conditions. In addition, we also discuss the possible machine learning (ML) approach to our future work direction to optimize the materials structures, and synthesis process parameters for future high-efficient perovskite solar cells fabrication.

Interface Defects Dependent on Perovskite Annealing Temperature for NiOX-Based Inverted CsPbI2Br Perovskite Solar Cells

Nickel oxide (NiOX) is an ideal inorganic hole transport material for the fabrication of inverted perovskite solar cells owing to its excellent optical and semiconductor properties. Currently, the main research on developing the performance of NiOX-based perovskite solar cells focuses on improving the conductivity of NiOX thin films and preventing the redox reactions between metal cations (Ni3+ on the surface of NiOX) and organic cations (FA+ or MA+ in the perovskite precursors) at the NiOX/perovskite interface. In this study, a new type of interface defects in NiOX-based CsPbI2Br solar cells is reported. That is the Pb2+ from CsPbI2Br perovskites can diffuse into the lattice of NiOX surface as the annealing temperature of perovskites changes. The diffusion of Pb2+ increases the ratio of Ni3+/Ni2+ on the surface of NiOX, leading to an increase in the density of trap state at the interface between NiOX and perovskites, which eventually results in a serious decline in the photovoltaic performance of solar cells.

Single Crystal Ruddlesden-Popper and Dion-Jacobson Metal Halide Perovskites for Visible Light Photodetectors: Present Status and Future Perspectives

2D metal halide perovskites (MHPs), mainly the studied Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases, have gained enormous popularity as optoelectronic materials owing to their self-assembled multiple quantum well structures, tunable semiconducting properties, and improved structural stability compared to their bulk 3D counterparts. The performance of polycrystalline thin film devices is limited due to the formation of defects and trap states. However, as studied so far, single crystal-based devices can provide a better platform to improve device performance and investigate their fundamental properties more reliably. This Review provides the first comprehensive report on the emerging field of RP and DJ perovskite single crystals and their use in visible light photodetectors of varied device configurations. This Review structurally summarizes the 2D MHP single crystal growth methods and the parameters that control the crystal growth process. In addition, the characterization techniques used to investigate their crystal properties are discussed. The review further provides detailed insights into the working mechanisms as well as the operational performance of 2D MHP single crystal photodetector devices. In the end, to outline the present status and future directions, this Review provides a forward-looking perspective concerning the technical challenges and bottlenecks associated with the developing field of RP and DJ perovskite single crystals. Therefore, this timely review will provide a detailed overview of the fast-growing field of 2D MHP single crystal-based photodetectors as well as ignite new concepts for a wide range of applications including solar cells, photocatalysts, solar H2 production, neuromorphic bioelectronics, memory devices, etc.

Perovskite versus Standard Photodetectors

Perovskites have been largely implemented into optoelectronics as they provide several advantages such as long carrier diffusion length, high absorption coefficient, high carrier mobility, shallow defect levels and finally, high crystal quality. The brisk technological development of perovskite devices is connected to their relative simplicity, high-efficiency processing and low production cost. Significant improvement has been made in the detection performance and the photodetectors' design, especially operating in the visible (VIS) and near-infrared (NIR) regions. This paper attempts to determine the importance of those devices in the broad group of standard VIS and NIR detectors. The paper evaluates the most important parameters of perovskite detectors, including current responsivity (R), detectivity (D*) and response time (τ), compared to the standard photodiodes (PDs) available on the commercial market. The conclusions presented in this work are based on an analysis of the reported data in the vast pieces of literature. A large discrepancy is observed in the demonstrated R and D*, which may be due to two reasons: immature device technology and erroneous D* estimates. The published performance at room temperature is even higher than that reported for typical detectors. The utmost D* for perovskite detectors is three to four orders of magnitude higher than commercially available VIS PDs. Some papers report a D* close to the physical limit defined by signal fluctuations and background radiation. However, it is likely that this performance is overestimated. Finally, the paper concludes with an attempt to determine the progress of perovskite optoelectronic devices in the future.

The Role of Optimal Electron Transfer Layers for Highly Efficient Perovskite Solar Cells-A Systematic Review

Perovskite solar cells (PSCs), which are constructed using organic-inorganic combination resources, represent an upcoming technology that offers a competitor to silicon-based solar cells. Electron transport materials (ETMs), which are essential to PSCs, are attracting a lot of interest. In this section, we begin by discussing the development of the PSC framework, which would form the foundation for the requirements of the ETM. Because of their exceptional electronic characteristics and low manufacturing costs, perovskite solar cells (PSCs) have emerged as a promising proposal for future generations of thin-film solar energy. However, PSCs with a compact layer (CL) exhibit subpar long-term reliability and efficacy. The quality of the substrate beneath a layer of perovskite has a major impact on how quickly it grows. Therefore, there has been interest in substrate modification using electron transfer layers to create very stable and efficient PSCs. This paper examines the systemic alteration of electron transport layers (ETLs) based on electron transfer layers that are employed in PSCs. Also covered are the functions of ETLs in the creation of reliable and efficient PSCs. Achieving larger-sized particles, greater crystallization, and a more homogenous morphology within perovskite films, all of which are correlated with a more stable PSC performance, will be guided by this review when they are developed further. To increase PSCs' sustainability and enable them to produce clean energy at levels previously unheard of, the difficulties and potential paths for future research with compact ETLs are also discussed.

Exploring the influence of pressure-induced semiconductor-to-metal transition on the physical properties of cubic perovskites FrXCl3 (X = Ge and Sn)

Even though lead halide perovskites have outstanding physiochemical properties and improved power conversion efficiency, most of these compounds threaten their future commercialization because of their instability and highly toxic nature. Thus, it is preferable to use stable alternative elements rather than lead to make environmentally friendly perovskite material that will have comparable optical and electronic properties to those constructed from Pb-based perovskites. However, devices constructed from lead-free perovskites typically display a lower power conversion efficiency. Applying hydrostatic pressure could be deemed an effective method to alter the physical properties of these compounds. This not only improves their performance in application but also reveals significant correlations between structure and properties. This work uses DFT to investigate the structural, electronic, optical, and elastic properties of non-toxic, francium-based halide perovskites FrXCl3 (X = Ge, Sn) at different levels of hydrostatic pressures that vary from 0 to 10 GPa. The estimated structural parameter's strong correlation with the data from earlier studies ensures the accuracy of the current findings. Pressure causes the Fr-Cl and Ge (Sn)-Cl bonds to shorten and become stronger. The electronic property calculations demonstrated that both compounds are direct band-gap semiconductors. The application of pressure leads to a linear reduction in the band gap (semiconducting to metallic state) and raises the electronic density of states around the Fermi level by forcing the valence band electrons upward, indicating that the optoelectronic device's performance can be tuned and improved. The values of the dielectric constant, absorptivity and reflectivity showed an increasing tendency with pressure. As the pressure applied to the compounds increases, the absorption spectra show a redshift. These findings suggested that the FrXCl3 (X = Ge and Sn) compound becomes more appropriate for usage in optoelectronic applications under pressure. Furthermore, our examination of the mechanical properties indicates that both FrGeCl3 and FrSnCl3 exhibit mechanically stability, and ductility. Interestingly, we observe an increase in ductility as pressure levels rise.

Mathematical Modeling and Optimization of Highly Efficient Nontoxic All-Inorganic CsSnGeI3-Based Perovskite Solar Cells with Oxide and Kesterite Charge Transport Layers

Despite exceptional optoelectronic properties and rapidly increasing efficiency of perovskite solar cells (PSCs), the issues of toxicity and device instability have hampered the commercialization of this renewable energy technology. Lead (Pb) being the main culprit creates major environmental risks and therefore must be replaced with a nontoxic material such as tin (Sn), germanium (Ge), etc. Moreover, replacing organic cations in the perovskite's ABX3 structure with inorganic ones like cesium (Cs) helps aid the stability issues. This study uses six different kesterite-based hole transport layers (HTLs) and three different metal oxide-based electron transport layers (ETLs) to numerically simulate and optimize all-inorganic CsSnGeI3 PSCs. Metal oxide ETLs are used in this study due to their large band gap, while kesterite HTLs are used due to their excellent conductive properties. All of the simulations are performed under standard testing conditions. A total of 18 novel planar (n-i-p) PSCs are modeled by the combination of various charge transport layers (CTLs), and the device optimization was done to enhance the power conversion efficiencies (PCEs) of the PSCs. Furthermore, the effect of CTLs on the energy band alignment, electric field, quantum efficiency, light absorption, and recombination rate is analyzed. Additionally, a detailed analysis of the impact of defect density (Nt), interface defects (ETL/Perv, Perv/HTL), temperature, and work function on the functionality of 18 different CsSnGeI3-based PSCs is conducted. The simulation findings demonstrate that SnO2/CsSnGeI3/CNTS is the most efficient optimized PSC among all of the simulated structures, with a PCE of 27.33%, Jsc of 28.04 mA/cm2, FF of 85%, and Voc of 1.14 V.

Elucidating Charge Carrier Dynamics in Perovskite-Based Tandem Solar Cells

Recently, multijunction tandem solar cells (TSCs) have presented high power conversion efficiency and revealed their immense potential in photovoltaic evolution. It is demonstrated that multiple light absorbers with various bandgap energies overcome the Shockley-Queisser limit of single-junction solar cells by absorbing the wide-range wavelength photons. Here, the main key challenges are reviewed, especially the charge carrier dynamics in perovskite-based 2-terminal (2-T) TSCs in terms of current matching, and how to manage these issues from a vantage point of characterization. To do this, the effect of recombination layers, optical and fabrication hurdles, and the impact of wide bandgap perovskite solar cells are discussed extensively. Afterward, this review focuses on various optoelectronics, spectroscopic, and theoretical (optical simulation) characterizations to figure out those issues, especially current-matching issues faced by the photovoltaic society. This review comprehensively provides deep insights into the relationship between the current-matching problems and the photovoltaic performance of TSCs through a variety of perspectives. Consequently, it is believed that this review is essential to address the main problems of 2-T TSCs, and the suggestions to elucidate the charge carrier dynamics and its characterization may pave the way to overcome such obstacles to further improve the development of 2-T TSCs in relation to the current-matching problems.

Challenges in the design and synthesis of self-assembling molecules as selective contacts in perovskite solar cells

Self-assembling molecules (SAMs), as selective contacts, play an important role in perovskite solar cells (PSCs), determining the performance and stability of these photovoltaic devices. These materials offer many advantages over other traditional materials used as hole-selective contacts, as they can be easily deposited on a large area of metal oxides, can modify the work function of these substrates, and reduce optical and electric losses with low material consumption. However, the most interesting thing about SAMs is that by modifying the chemical structure of the small molecules used, the energy levels, molecular dipoles, and surface properties of this assembled monolayer can be modulated to fine-tune the desired interactions between the substrate and the active layer. Due to the important role of organic chemistry in the field of photovoltaics, in this review, we will cover the current challenges for the design and synthesis of SAMs PSCs. Discussing, the structural features that define a SAM, (ii) disclosing how commercial molecules inspired the synthesis of new SAMs; and (iii) detailing the pros- and cons- of the reported synthetic protocols that have been employed for the synthesis of molecules for SAMs, helping synthetic chemists to develop novel structures and promoting the fast industrialization of PSCs.

Perovskite Solar Cells: A Review of the Latest Advances in Materials, Fabrication Techniques, and Stability Enhancement Strategies

Perovskite solar cells (PSCs) are gaining popularity due to their high efficiency and low-cost fabrication. In recent decades, noticeable research efforts have been devoted to improving the stability of these cells under ambient conditions. Moreover, researchers are exploring new materials and fabrication techniques to enhance the performance of PSCs under various environmental conditions. The mechanical stability of flexible PSCs is another area of research that has gained significant attention. The latest research also focuses on developing tin-based PSCs that can overcome the challenges associated with lead-based perovskites. This review article provides a comprehensive overview of the latest advances in materials, fabrication techniques, and stability enhancement strategies for PSCs. It discusses the recent progress in perovskite crystal structure engineering, device construction, and fabrication procedures that has led to significant improvements in the photo conversion efficiency of these solar devices. The article also highlights the challenges associated with PSCs such as their poor stability under ambient conditions and discusses various strategies employed to enhance their stability. These strategies include the use of novel materials for charge transport layers and encapsulation techniques to protect PSCs from moisture and oxygen. Finally, this article provides a critical assessment of the current state of the art in PSC research and discusses future prospects for this technology. This review concludes that PSCs have great potential as a low-cost alternative to conventional silicon-based solar cells but require further research to improve their stability under ambient conditions in view of their definitive commercialization.

A DFT investigation of lead-free TlSnX3 (X = Cl, Br, or I) perovskites for potential applications in solar cells and thermoelectric devices

In the present study, the Density Functional Theory (DFT) was employed to computationally investigate the potential application of newly developed lead-free perovskites with the formula of TlSnX3 (X = Cl, Br, or I) as absorbers in the perovskite solar cells and as thermoelectric materials. The Quantum Espresso code was implemented to optimize the structural configuration of the perovskites and to compute a range of their properties, including their elasticity, electronic behavior, optical characteristics, and thermoelectric attributes. The findings indicated that these perovskite materials exhibit both chemical and structural stability and that TlSnBr3 and TlSnI3 perovskites possess high dynamic stability. The findings additionally revealed direct (R → R) band gap energy values of 0.87 eV for TlSnCl3, 0.52 eV for TlSnBr3, and 0.28 eV for TlSnI3 using the GGA-PBE functional. Further analysis of their elastic properties suggested that these materials are mechanically stable and displayed overall ductile behaviour. They also demonstrated remarkable optical properties, particularly a high absorption coefficient, ranging from 105 cm-1 to 106 cm-1. Consequently, it is reasonable to infer that these materials exhibit considerable potential for utilization in solar cells. Finally, the evaluation of their thermoelectric properties has revealed the highly promising potential of these materials to be employed in thermoelectric applications.

Electronic and structural properties of mixed-cation hybrid perovskites studied using an efficient spin-orbit included DFT-1/2 approach

Fundamental understanding and optimization of the emerging mixed organic-inorganic hybrid perovskites for solar cells require multiscale modeling starting from ab initio quantum mechanics methods. Particularly, it is important to correctly predict the structural and electronic properties such as phase stability, lattice parameters, band gaps, and band structures. Although density functional theory is the method of choice to address these properties and generate the input for subsequent multiscale, high-throughput, and data-driven approaches, standard exchange correlation functionals fail to reproduce the bandgap, particularly if spin-orbit coupling (SOC) is correctly taken into account. While many SOC-included hybrid functionals suffer from low transferability between different molecular ions and are computationally costly, we propose an efficient multistep simulation protocol based on the DFT-1/2 method. We apply this approach to APbI3 with A: FA, MA, Cs, and systems with mixed cations and show how the choice of the A-cation modifies the Pb-I scaffold and the hydrogen bonding and discuss their interplay with structural stability. Furthermore, band gaps, band structures, Rashba band splitting, Born effective charges as well as partial density of states (PDOS) are compared for different cases w/wo the SOC effect and the DFT-1/2 approach.

Leveraging machine learning to consolidate the diversity in experimental results of perovskite solar cells

Perovskite solar cells offer great potential for smart energy applications due to their flexibility and solution processability. However, the use of solution-based techniques has resulted in significant variations in device fabrication, leading to inconsistent results on the same composition. Machine learning (ML) and data science offer a potential solution to these challenges by enabling the automated design of perovskite solar cells. In this study, we leveraged machine learning tools to predict the band gap of hybrid organic-inorganic perovskites (HOIPs) and the power conversion efficiency of their solar cell devices. By analyzing 42 000 experimental datasets, we developed ML models for perovskite device design through a two-step predicting method, enabling the automation of perovskite materials development and device optimization. Additionally, band gap dependence of device parameters from experimental data is also validated, as predicted by the Shockley-Queisser model. This work has the potential to streamline the development of perovskite solar cells (PSCs) and optimize their performance without relying on time-consuming trial-and-error approaches.

Effect of substituent structure in fluorene based compounds: Experimental and theoretical study

Fluorene-based low molar weight derivatives were synthesized in Suzuki reactions by using key starting materials 9-benzylidene-2,7-dibromofluorene or 3-(2,7-dibromofluoren-9-ylmethylen)-9-ethylcarbazole and various aryl boronic acids. Photophysical properties of the compounds were investigated in different solutions as well as in solid state. The thermal investigations showed that the obtained compounds are highly thermally stable with temperatures of 5% mass loss (T_5%) in the range of 311-432 °C. Some of the compounds also exhibited very high glass transition temperatures exceeding 125 °C. The presented molecules were electrochemically active and showed the energy band gap below 2.97 eV. The investigations were supported by DFT calculations and the photovoltaic ability of the presented compounds was tested in the organic-inorganic solar cells.

Nickel oxide morphology synthesized with a hydrothermal method for inverted perovskite solar cells

In this paper, a hydrothermal method is used to synthesize a nickel oxide nanostructure (nano-NiO) for its application to inverted perovskite solar cells. These pore nanostructures were employed to increase both the contact and channel between the hole transport and perovskite layers of an ITO/nano-N i O/C H ₃ N H ₃ P b I ₃/P C B M/A g device. The purpose of this research is twofold. First, three different nano-NiO morphologies were synthesized at temperatures of 140°C, 160°C, and 180°C. Then, a Raman spectrometer was used to check the phonon vibration and magnon scattering characteristics after an annealing temperature of 500°C. Second, nano-NiO powders were dispersed in isopropanol for subsequent spin coating on the inverted solar cells. The nano-NiO morphologies were multi-layer flakes, microspheres, and particles at synthesis temperatures of 140°C, 160°C, and 180°C, respectively. When the microsphere nano-NiO was used as the hole transport layer, the perovskite layer had a larger coverage of 83.9%. The grain size of the perovskite layer was analyzed by x-ray diffraction, and strong crystal orientations of (110) and (220) peaks were found. Despite this, the power conversion efficiency could affect the promotion, which is 1.37 times higher than the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate element conversion efficiency of the planar structure.

Formamidinium Lead Iodide Perovskite Thin Films Formed by Two-Step Sequential Method: Solvent-Morphology Relationship

Thin films made of formamidinium lead iodide (FAPbI₃) perovskites prepared by a two-step sequential deposition method using various solvents for formamidinium iodide (FAI) - isopropanol, n-butanol and tert-butanol, were studied with the aim of finding a correlation between morphology and solvent properties to improve film quality. They were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and their photophysical properties were studied by means of absorption and photoluminescence (PL) spectroscopies. XRD patterns, absorption and PL spectra proved α-phase formation for all selected solvents. An excessive amount of PbI₂ found in perovskite films prepared with n-butanol indicates incomplete conversion. Thin film morphology, such as grain and crystallite size, depended on the solvent. Using tert-butanol, thin films with a very large grain size of up to several micrometers and with preferred crystallite orientation were fabricated. The grain size increased as follows: 0.2-0.5, 0.2-1 and 2-5 µm for isopropanol, n-butanol and tert-butanol, respectively. A correlation between the grain size and viscosity, electric permittivity and polarizability of the solvent could be considered. Our results, including fabrication of perovskite films with large grains and fewer grain boundaries, are important and of interest for many optoelectronic applications.