Perovskite Solar Cells: Progress and Advancements

Mapping Surface-Defect and Ions Migration in Mixed-Cation Perovskite Crystals

Single crystal perovskites have garnered significant attention as potential replacements for existing absorber layer materials. Despite the extensive investigations on their photoinduced charge-carriers dynamics, most of the time-resolved techniques focus on bulk properties, neglecting surface characteristic which plays a crucial role for their optoelectronic performance. Herein, 4D ultrafast scanning electron microscopy (4D-USEM) is utilized to probing the photogenerated carrier transport at the first few nanometers, alongside density functional theory (DFT) to track both defect centers and ions migration. Two compositions of mixed cation are investigated: FA0.6MA0.4PbI3 and FA0.4MA0.6PbI3, interestingly, the former displays a longer lifetime compared to the latter due the presence of a higher surface-defect centers. DFT calculations fully support that revealing samples with higher FA content have a lower energy barrier for iodide ions to migrate from the bulk to top layer, assisting in passivating surface vacancies, and a higher energy diffusion barrier to escape from surface to vacuum, resulting in fewer vacancies and longer-lived hole-electron pairs. These findings manifest the influence of cation selection on charge carrier transport and formation of defects, and emphasize the importance of understanding ion migrations role in controlling surface vacancies to assist engineering high-performance optoelectronic devices based on single crystal perovskites.

A comprehensive review on the advancements and challenges in perovskite solar cell technology

Perovskite solar cells (PSCs) have emerged as revolutionary technology in the field of photovoltaics, offering a promising avenue for efficient and cost-effective solar energy conversion. This review provides a comprehensive overview of the progress and developments in PSCs, beginning with an introduction to their fundamental properties and significance. Herein, we discuss the various types of PSCs, including lead-based, tin-based, mixed Sn-Pb, germanium-based, and polymer-based PSCs, highlighting their unique attributes and performance metrics. Special emphasis is given to halide double PSCs and their potential in enhancing the stability of PSCs. Charge transport layers and their significance in influencing the overall efficiency of solar cells are discussed in detail. The review also explores the role of tandem solar cells as a solution to overcome the limitations of single-junction solar cells, offering an integrated approach to harness a broader spectrum of sunlight. This review concludes with challenges associated with PSCs and perspective on the future potential of PSCs, emphasizing their role in shaping a sustainable energy landscape. Through this review readers will gain a comprehensive insight into the current state-of-the-art in PSC technology and the avenues for future research and development.

Harnessing the potential of CsPbBr3-based perovskite solar cells using efficient charge transport materials and global optimization

Perovskite solar cells (PSCs) have become a possible alternative to traditional photovoltaic devices for their high performance, low cost, and ease of fabrication. Here in this study, the SCAPS-1D simulator numerically simulates and optimizes CsPbBr₃-based PSCs under the optimum illumination situation. We explore the impact of different back metal contacts (BMCs), including Cu, Ag, Fe, C, Au, W, Pt, Se, Ni, and Pd combined with the TiO₂ electron transport layer (ETL) and CFTS hole transport layer (HTL), on the performance of the devices. After optimization, the ITO/TiO₂/CsPbBr₃/CFTS/Ni structure showed a maximum power conversion efficiency (PCE or η) of 13.86%, with Ni as a more cost-effective alternative to Au. After the optimization of the BMC the rest of the investigation is conducted both with and without HTL mode. We investigate the impact of changing the thickness and the comparison with acceptor and defect densities (with and without HTL) of the CsPbBr₃ perovskite absorber layer on the PSC performance. Finally, we optimized the thickness, charge carrier densities, and defect densities of the absorber, ETL, and HTL, along with the interfacial defect densities at HTL/absorber and absorber/ETL interfaces to improve the PCE of the device; and the effect of variation of these parameters is also investigated both with and without HTL connected. The final optimized configuration achieved a V_OC of 0.87 V, J_SC of 27.57 mA cm^-2, FF of 85.93%, and PCE of 20.73%. To further investigate the performance of the optimized device, we explore the impact of the temperature, shunt resistance, series resistance, capacitance, generation rate, recombination rate, Mott-Schottky, JV, and QE features of both with and without HTL connected. The optimized device offers the best thermal stability at a temperature of 300 K. Our study highlights the potential of CsPbBr₃-based PSCs and provides valuable insights for their optimization and future development.

Direct In Situ Conversion of Lead Iodide to a Highly Oriented and Crystallized Perovskite Thin Film via Sequential Deposition for 23.48% Efficient and Stable Photovoltaic Devices

In the sequential deposition method of perovskite films, the crystallinity and microstructure of PbI2 are often sacrificed to solve the problem of an incomplete reaction between organic halide and lead halide. As a result, the crystal orientation of the perovskite film prepared by the sequential deposition method is generally worse than that of the perovskite film prepared by a one-step antisolvent method. Here, we preplaced formamidine formate (FAFa) on the buried interface to regulate the formation mechanism from PbI2 to perovskite. As shown by the XPS measurement of the perovskite buried interface, the HCOO- anion of FAFa first partially replaces I- to coordinate with Pb2+. With the subsequent annealing process, some HCOO- anions were released and migrated upward, which promoted the recrystallization of PbI2, obtaining a PbI2 film with enhanced crystallinity and orientation. Additionally, the lift-off process proves that the HCOO- anions suppress the anion vacancy defects enriched at the buried interface and promote charge transport because the HCOO- anions are small enough to adapt to the iodide vacancy. Grazing incidence wide-angle X-ray scattering and X-ray diffraction measurements show that the in situ conversion mechanism is responsible for the PbI2-to-perovskite process, resulting in the highly oriented perovskite film without increasing the residual PbI2 content in the perovskite film. As a result, our strategies enabled a champion power conversion efficiency of 23.48% with improved storage stability and photostability. This work provides a new strategy to improve the crystallinity of sequential deposition perovskites without destabilizing the device due to more PbI2 residues.

Optoelectronic Enhancement of Perovskite Solar Cells through the Incorporation of Plasmonic Particles

The optoelectronic advantages of anchoring plasmonic silver and copper particles and non-plasmonic titanium particles onto zinc oxide (ZnO) nanoflower (NF) scaffolds for the fabrication of perovskite solar cells (PSCs) are addressed in this article. The metallic particles were sputter-deposited as a function of sputtering time to vary their size on solution-grown ZnO NFs on which methylammonium lead iodide perovskite was crystallized in a controlled environment. Optical absorption measurements showed impressive improvements in the light-harvesting efficiency (LHE) of the devices using silver nanoparticles and some concentrations of copper, whereas the LHE was relatively lower in devices used titanium than in a control device without any metallic particles. Fully functional PSCs were fabricated using the plasmonic and non-plasmonic metallic film-decorated ZnO NFs. Several fold enhancements in photoconversion efficiency were achieved in the silver-containing devices compared with the control device, which was accompanied by an increase in the photocurrent density, photovoltage, and fill factor. To understand the plasmonic effects in the photoanode, the LHE, photo-current density, photovoltage, photoluminescence, incident photon-to-current conversion efficiency, and electrochemical impedance properties were thoroughly investigated. This research showcases the efficacy of the addition of plasmonic particles onto photo anodes, which leads to improved light scattering, better charge separation, and reduced electron–hole recombination rate.

Hysteresis in hybrid perovskite indoor photovoltaics

Halide perovskite indoor photovoltaics (PV) are a viable solution to autonomously power the billions of sensors in the huge technology field of the Internet of Things. However, there exists a knowledge gap in the hysteresis behaviour of these photovoltaic devices under indoor lighting conditions. The present work is the first experimental study dedicated to exploring the degree of hysteresis in halide perovskite indoor photovoltaic devices by carrying out both transient J-V scan and steady state maximum power point tracking (MPPT) measurements. Dependence of hysteresis on device architecture, selection of electron transporting layers and the composition of the perovskite photoactive layers were investigated. Under indoor illumination, the p-i-n MAPbI₃-based devices show consistently high power conversion efficiency (PCE) (stabilized PCE) of greater than 30% and negligible hysteresis behaviour, whereas the n-i-p MAPbI₃ devices show poor performance (stabilized PCE ∼ 15%) with pronounced hysteresis effect. Our study also reveals that the n-i-p triple cation perovskite devices are more promising (stabilized PCE ∼ 25%) for indoor PV compared to n-i-p MAPbI₃ due to their suppressed ion migration effects. It was observed that the divergence of the PCE values estimated from the J-V scan measurements, and the maximum power point tracking method is higher under indoor illumination compared to 1 Sun, and hence for halide perovskite-based indoor PV, the PCE from the MPPT measurements should be prioritized over the J-V scan measurements. The results from our study suggest the following approaches for maximizing the steady state PCE from halide perovskite indoor PV: (i) select perovskite active layer composition with suppressed ion migration effects (such as Cs-containing triple cation perovskites) and (ii) for the perovskite composition such as MAPbI₃, where the ion migration is very active, p-i-n architecture with organic charge transport layers is beneficial over the n-i-p architecture with conventional metal oxides (such as TiO₂, SnO₂) as charge transport layers. This article is part of the theme issue 'Developing resilient energy systems'.

Developments on Perovskite Solar Cells (PSCs): A Critical Review

This review provides detailed information on perovskite solar cell device background and monitors stepwise scientific efforts applied to improve device performance with time. The work reviews previous studies and the latest developments in the perovskite crystal structure, electronic structure, device architecture, fabrication methods, and challenges. Advantages, such as easy bandgap tunability, low charge recombination rates, and low fabrication cost, are among the topics discussed. Some of the most important elements highlighted in this review are concerns regarding commercialization and prototyping. Perovskite solar cells are generally still lab-based devices suffering from drawbacks such as device intrinsic and extrinsic instabilities and rising environmental concerns due to the use of the toxic inorganic lead (Pb) element in the perovskite (ABX3) light-active material. Some interesting recommendations and possible future perspectives are well articulated.

Wide-Bandgap Halide Perovskites for Indoor Photovoltaics

Indoor photovoltaics (IPVs) are receiving great research attention recently due to their projected application in the huge technology field of Internet of Things (IoT). Among the various existing photovoltaic technologies such as silicon, Cadmium Telluride (CdTe), Copper Indium Gallium Selenide (CIGS), organic photovoltaics, and halide perovskites, the latter are identified as the most promising for indoor light harvesting. This suitability is mainly due to its composition tuning adaptability to engineer the bandgap to match the indoor light spectrum and exceptional optoelectronic properties. Here, in this review, we are summarizing the state-of-the-art research efforts on halide perovskite-based indoor photovoltaics, the effect of composition tuning, and the selection of various functional layer and device architecture onto their power conversion efficiency. We also highlight some of the challenges to be addressed before these halide perovskite IPVs are commercialized.

Air-Processed Infrared-Annealed Printed Methylammonium-Free Perovskite Solar Cells and Modules Incorporating Potassium-Doped Graphene Oxide as an Interlayer

The use of solution processes to fabricate perovskite solar cells (PSCs) represents a winning strategy to reduce capital expenditure, increase the throughput, and allow for process flexibility needed to adapt PVs to new applications. However, the typical fabrication process for PSC development to date is performed in an inert atmosphere (nitrogen), usually in a glovebox, hampering the industrial scale-up. In this work, we demonstrate, for the first time, the use of double-cation perovskite (forsaking the unstable methylammonium (MA) cation) processed in ambient air by employing potassium-doped graphene oxide (GO-K) as an interlayer, between the mesoporous TiO₂ and the perovskite layer and using infrared annealing (IRA). We upscaled the device active area from 0.09 to 16 cm² by blade coating the perovskite layer, exhibiting power conversion efficiencies (PCEs) of 18.3 and 16.10% for 0.1 and 16 cm² active area devices, respectively. We demonstrated how the efficiency and stability of MA-free-based perovskite deposition in air have been improved by employing GO-K and IRA.

Indium Doping of Lead-Free Perovskite Cs2SnI6

Structure and properties of an inorganic perovskite Cs₂SnI₆ demonstrated its potential as a light-harvester or electron-hole transport material; however, its optoelectronic properties are poorer than those of lead-based perovskites. Here, we report the way of light tuning of absorption and transport properties of cesium iodostannate(IV) Cs₂SnI₆ via partial heterovalent substitution of tin for indium. Light absorption and optical bandgaps of materials have been investigated by UV-vis absorption and photoluminescent spectroscopies. Low-temperature electron paramagnetic resonance spectroscopy was used to study the kind of paramagnetic centers in materials.

Arrays of Plasmonic Nanostructures for Absorption Enhancement in Perovskite Thin Films

We report optical characterization and theoretical simulation of plasmon enhanced methylammonium lead iodide (MAPbI 3 ) thin-film perovskite solar cells. Specifically, various nanohole (NH) and nanodisk (ND) arrays are fabricated on gold/MAPbI 3 interfaces. Significant absorption enhancement is observed experimentally in 75 nm and 110 nm-thick perovskite films. As a result of increased light scattering by plasmonic concentrators, the original Fabry-Pérot thin-film cavity effects are suppressed in specific structures. However, thanks to field enhancement caused by plasmonic resonances and in-plane interference of propagating surface plasmon polaritons, the calculated overall power conversion efficiency (PCE) of the solar cell is expected to increase by up to 45.5%, compared to its flat counterpart. The role of different geometry parameters of the nanostructure arrays is further investigated using three dimensional (3D) finite-difference time-domain (FDTD) simulations, which makes it possible to identify the physical origin of the absorption enhancement as a function of wavelength and design parameters. These findings demonstrate the potential of plasmonic nanostructures in further enhancing the performance of photovoltaic devices based on thin-film perovskites.

Elucidation of the role of guanidinium incorporation in single-crystalline MAPbI3 perovskite on ion migration and activation energy

We have studied the effect of guanidinium incorporation in a single-crystalline MAPbI₃ perovskite on ion migration using temperature-dependent electrochemical impedance spectroscopy.

Impact of Electron-Phonon Scattering on Optical Properties of CH3NH3PbI3 Hybrid Perovskite Material

We numerically investigate the impact of electron-phonon scattering on the optical properties of a perovskite material (CH₃NH₃PbI₃). Using nonequilibrium Green function formalism, we calculate the local density of states for several values of the electron-phonon scattering strength. We report an Urbach-like penetration of the density of states in the band gap due to scattering. A physical analytical model allows us to attribute this behavior to a multiphonon process. Values of Urbach energy up to 9.5 meV are obtained, meaning that scattering contribution to the total experimental Urbach energy of 15 meV is quite important. We also show that the open-circuit voltage V _oc, for a solar cell assuming such a material as an absorber, depends on the scattering strength. V _oc loss increases with the scattering strength, up to 41 mV. Finally, an unexpected result of this study, is that the impact of electron-phonon scattering on Urbach tail and V _oc increases with the phonon energy. This low value in perovskite (8 meV) is therefore an advantage for photovoltaic applications.

Environmental Performance of Emerging Photovoltaic Technologies: Assessment of the Status Quo and Future Prospects Based on a Meta-Analysis of Life-Cycle Assessment Studies

Emerging photovoltaic technologies are expected to have lower environmental impacts during their life cycle due to their extremely thin-film technology and resulting material savings. The environmental impacts of four emerging photovoltaics were investigated based on a meta-analysis of life-cycle assessment (LCA) studies, comprising a systematic review and harmonization approach of five key indicators to describe the environmental status quo and future prospects. The status quo was analyzed based on a material-related functional unit of 1 watt-peak of the photovoltaic cell. For future prospects, the functional unit of 1 kWh of generated electricity was used, including assumptions on the use phase, notably on the lifetime. The results of the status quo show that organic photovoltaic technology is the most mature emerging photovoltaic technology with a competitive environmental performance, while perovskites have a low performance, attributed to the early stage of development and inefficient manufacturing on the laboratory scale. The results of future prospects identified improvements of efficiency, lifetime, and manufacturing with regard to environmental performance based on sensitivity and scenario analyses. The developed harmonization approach supports the use of LCA in the early stages of technology development in a structured way to reduce uncertainty and extract significant information during development.

Stability of organometal halide perovskite solar cells and role of HTMs: recent developments and future directions

Perovskite solar cells (PSCs) have recently emerged as one of the most exciting fields of research of our time, and the World Economic Forum in 2016 recognized them as one of the top 10 technologies in 2016. With 22.7% power conversion efficiency, PSCs are poised to revolutionize the way power is produced, stored and consumed. However, the widespread use of PSCs requires addressing the stability issue. Therefore, it is now time to focus on the critical step i.e. stability under the operating conditions for the development of a sustainable and durable PV technology based on PSCs. In order to improve the stability of PSCs, hole transport materials (HTMs) have been considered as the paramount components. This is due to the fact that most of the organic HTMs possess a hygroscopic and acidic nature that leads to poor stability of the PSCs. This article reviews briefly but comprehensively the environmental stability issues of PSCs, fundamentals, strategies for improvement, the role of HTMs towards stability and various types of HTMs. Also the environmental parameters affecting the performance of perovskite solar cells including temperature, moisture and light soaking environment have been considered.

Perovskite Solar Cells with ZnO Electron-Transporting Materials

Perovskite solar cells (PSCs) have developed rapidly over the past few years, and the power conversion efficiency of PSCs has exceeded 20%. Such high performance can be attributed to the unique properties of perovskite materials, such as high absorption over the visible range and long diffusion length. Due to the different diffusion lengths of holes and electrons, electron transporting materials (ETMs) used in PSCs play a critical role in PSCs performance. As an alternative to TiO₂ ETM, ZnO materials have similar physical properties to TiO₂ but with much higher electron mobility. In addition, there are many simple and facile methods to fabricate ZnO nanomaterials with low cost and energy consumption. This review focuses on recent developments in the use of ZnO ETM for PSCs. The fabrication methods of ZnO materials are briefly introduced. The influence of different ZnO ETMs on performance of PSCs is then reviewed. The limitations of ZnO ETM-based PSCs and some solutions to these challenges are also discussed. The review provides a systematic and comprehensive understanding of the influence of different ZnO ETMs on PSCs performance and potentially motivates further development of PSCs by extending the knowledge of ZnO-based PSCs to TiO₂ -based PSCs.

A high performance and low-cost hole transporting layer for efficient and stable perovskite solar cells

A F4TCNQ doped FDT HTL based PSC demonstrates 75% higher device stability than a conventional Li-TFSI doped FDT based PSC.