Mesoscopic Perovskite Solar Cells Research Articles

Crystallization Control Assists Annealing‐Free Fabrication of Printable Mesoscopic Perovskite Solar Cells with Power Conversion Efficiency over 17%

The one‐step drop‐casting for preparing perovskite films in three‐layer mesoporous for printable mesoscopic perovskite solar cells always results in insufficient filling of mesopores. A binary solvent based on 2‐methoxyethanol (2‐ME) and 1‐methyl‐2‐pyrrolidone (NMP) offers a method suitable for annealing‐free to prepare dense perovskite films in mesopores. The crystallization process of perovskite films in mesopores can be adjusted by the content of NMP in the solvent. The introduction of NMP enhances the density of the perovskite film based on the binary solvent system, optimizing the contact between the perovskite film and the mesoporous scaffold. When the ratio of 2‐ME to NMP is 9:1, the optimal device achieves impressive performance metrics, including a power conversion efficiency (PCE) of 17.28%, an open‐circuit voltage of 0.98 V, a short‐circuit current of 23.80 mA cm−2, and a fill factor of 74.08%. This represents the highest PCE achieved to date in the annealing‐free preparation of perovskite films for printable mesoscopic perovskite solar cells. Furthermore, devices based on this binary solvent system exhibit remarkable stability, with almost no loss in efficiency even after 120 days of storage in an air environment without encapsulation.

Bifunctional passivation by lewis-base molecules for efficient printable mesoscopic perovskite solar cells

Printable mesoscopic perovskite solar cells (PM-PSCs) possess notable merits in terms of cost-effectiveness, easy manufacturing, and large scale applications. Nevertheless, the absence of a hole transport layer contributes to the exacerbation of carrier recombination, and the defects between the perovskite and electron transport layer (ETL) interfaces significantly decrease the efficiency of the devices. In this study, a bifunctional surface passivation approach is proposed by applying a thioacetamide (TAA) surfactant on the mesoporous TiO2 interface. The results demonstrate that TAA molecules could interact with TiO2, thereby diminishing the oxygen vacancy defects. Additionally, the amino group and sulfur atoms in TAA molecules act as Lewis base to effectively passivate the uncoordinated Pb2+ in perovskite and improve the morphology of perovskite, and decrease the trap-state density of perovskite. The TAA passivation mechanism improves the alignment of energy levels between TiO2 and perovskite, facilitating electron transport and reducing carrier recombination. Consequently, the TAA-passivated device achieved a champion power conversion efficiency (PCE) of 17.86% with a high fill factor (FF) of 79.16% and an open-circuit voltage (VOC) of 0.971 V. This investigation presents a feasible strategy for interfacial passivation of the ETL to further improve the efficiency of PM-PSCs.

Efficient Carbon‐Based Hole‐Conductor‐Free Printable Mesoscopic Perovskite Solar Cells via a Multifunctional Fluorinated Molecule

AbstractBenefiting from their simple and cost‐effective fabrication procedures, printable mesoscopic perovskite solar cells (p‐MPSCs) exhibit substantial potential for large‐scale production. In p‐MPSCs, the thickness of the perovskite filled in the TiO2 and ZrO2 mesoporous layers is ≈3 µm. Therefore, the perovskite crystallization process is more intricate and challenging in the mesoporous structure than the general planar thin film (0.3–0.5 µm). In this work, a multifunctional fluorinated molecule is applied to work as an additive to improve the perovskite crystallization, enhance the device efficiency, and elevate the operational stability. This additive forms robust coordination between its carbonyl groups and uncoordinated Pb2+, thereby effectively passivating defects. The hydrophobic properties of the fluorinated molecule contribute to the device's water‐resistant capability and long‐term operational stability. With these synergistic effects, the power conversion efficiency (PCE) of small‐area cells (0.1 cm2) reaches 20.15% under 1 sun illumination. Large‐area modules (56.4 cm2) are fabricated and exhibit a PCE of 15.41%.

Dual Defect Passivation at the Buried Interface for Printable Mesoscopic Perovskite Solar Cells with Reduced Open-Circuit Voltage Loss.

Numerous defects exist at the buried interface between the perovskite and adjacent electron transport layers in perovskite solar cells, resulting in severe non-radiative recombination and excessive open-circuit voltage (VOC) loss. Herein, a dual defect passivation strategy utilizing guanidine sulfate (GUA2SO4) as an interface modifier is first reported. On the one hand, the SO4 2- preferentially interacts with Pb-related defects, generating water-insoluble lead oxysalts complexes. Additionally, GUA+ diffuses into the perovskite and induces the formation of low-dimensional perovskite. These reactions effectively suppress trap states at the buried interface and perovskite boundaries in printable mesoscopic perovskite solar cells (p-MPSCs), thus increasing the carrier lifetime. Meanwhile, GUA2SO4 optimizes the interface energy band alignment, thus accelerating the charge extraction and transfer at the buried interface. This synergistic effect of trap passivation and interface energy band alignment modulation is strongly demonstrated by an increase in average VOC of 70mV and the power conversion efficiency improvement from 17.51% to 18.70%. This work provides a novel approach to efficiently improve the performance of p-MPSCs through dual-targeted defect passivation at the buried interface.

Design and upgrade of mesoporous perovskite solar cells

In recent years, there has been notable progress in the development of perovskite solar cells (PSCs), marked by significant advancements in efficiency, stability, and scalability. Among different device architectures and technical routes, mesoporous perovskite solar cells (MPSCs) based on TiO2/ZrO2/carbon scaffold and screen-printing fabrication process have shown unique advantages for mass production and commercialization due to the low material cost and scalable fabrication process. Through efforts on material optimization, interface engineering, and device design, the power conversion efficiency of MPSCs has steadily increased from the initial 6.64 ​% in 2013 to current 22.22 ​%. Attributing to the screen-printing-based fabrication process, printable mesoscopic PSCs have enabled large-area devices, from mini-modules to modules, and solar panels. In this review, we discuss the development and latest advances of MPSCs, and provide outlooks for further improving the performance of this promising photovoltaic technology.

Fine tuning of Nb-incorporated TiO2 thin films by atomic layer deposition and application as efficient electron transport layer in perovskite solar cells

Access to finely tuned thin films that can act as electron transport layer (ETL) and adapt to the absorber composition and whole cell fabrication process is key to achieve efficient perovskite-based solar cells. In this study, the growth of mixed niobium-titanium oxide (Nb-TiO2) thin films by atomic layer deposition and its use to extract photogenerated electrons is reported. Films were obtained at 200 °C from titanium (IV) i-propoxide, (t-butylimido)tris(diethylamido)niobium(V), and water by introducing Nb2O5 growth cycle in a TiO2 matrix. Process parameters (order of precursor introduction, cycle ratio) were optimized; the growth mechanism and the effective Nb incorporation were investigated by an in situ quartz crystal microbalance and x-ray photoelectron spectroscopy. The composition, morphology, structural, and optoelectronic properties of the as-deposited films were determined using a variety of characterization techniques. As a result, a fine control of the film properties (between TiO2 and Nb2O5 ones) could be achieved by tuning Nb content. To allow a successful implementation in solar devices, a comprehensive annealing study under several conditions (temperatures, various atmospheres) was conducted leading to an evolution of the optical properties due to a morphological change. Ultimately, the incorporation of these 15 nm-thick films in mesoscopic perovskite solar cells as ETL shows an improvement of the cell performances and of their stability with increasing Nb content, in comparison of both TiO2 and Nb2O5 pure compounds, reaching power conversion efficiency up to 18.3% and a stability above 80% of its nominal value after 138 h under illumination.

Electron injection and defect passivation for high-efficiency mesoporous perovskite solar cells.

Printable mesoscopic perovskite solar cells (p-MPSCs) do not require the added hole-transport layer needed in traditional p-n junctions but have also exhibited lower power conversion efficiencies of about 19%. We performed device simulation and carrier dynamics analysis to design a p-MPSC with mesoporous layers of semiconducting titanium dioxide, insulating zirconium dioxide, and conducting carbon infiltrated with perovskite that enabled three-dimensional injection of photoexcited electrons into titanium dioxide for collection at a transparent conductor layer. Holes underwent long-distance diffusion toward the carbon back electrode, and this carrier separation reduced recombination at the back contact. Nonradiative recombination at the bulk titanium dioxide/perovskite interface was reduced by ammonium phosphate modification. The resulting p-MPSCs achieved a power conversion efficiency of 22.2% and maintained 97% of their initial efficiency after 750 hours of maximum power point tracking at 55 ± 5°C.

Quantifying Infiltration for Quality Control in Printed Mesoscopic Perovskite Solar Cells: A Microscopic Perspective.

Mesoscopic carbon-based perovskite solar cells (CPSCs) are often cited as a potential frontrunner to perovskite commercialization. Infiltration, the extent to which perovskite fills the mesoporous scaffold, is critical for optimum performance and stability. However, infiltration data are usually presented as qualitative photographic comparisons of samples with extreme infiltration variation. This work examines how small infiltration defects impact performance using an optical microscopy examination of the base TiO2 layer to identify issues and develop targeted techniques for infiltration enhancement. Critically, the uninfiltrated area at the base of the stack was found to correlate well with PCE across multiple batches of varied print quality and ZrO2 thickness. Through reduction of mesh mark defects and improvement of print quality in the ZrO2 and carbon layers, a champion PCE of 15.01% is attained. It follows that this facile, multiscaled, nondestructive technique could enable targeted performance enhancement and quality control in future scale-up initiatives.

Improved Interfacial Contact Between “Perovskite/Electron‐Transport Layer” by Hydrophilic Molecule to Achieve Efficiency >14%, Carbon Electrode‐Based, Hole‐Conductor‐Free, Low‐Temperature Mesoscopic Perovskite Solar Cells

Interfacial contact between “perovskite/electron‐transport layer” (PVSK/ETL) has appeared as a bottleneck for the hole‐conductor‐free, mesoscopic perovskite solar cells (meso‐CPSCs) based on carbon electrode, especially for the low‐temperature devices. To solve this problem, hydroxypropyl‐β‐cyclodextrin is imported to TiO2‐based ETL. It is observed that this treatment improves the wettability of ETL, enhances the crystallization processes of PVSK in the mesoporous skeleton, and strengthens the interfacial contact between “PVSK/ETL”. Besides, defects are reduced at the interface. Accordingly, charge extraction is accelerated, while recombination is retarded. Transient photovoltage/photocurrent decay curve test shows that the charge‐extraction time decreases from 3.75 (±0.38) to 3.42 (±0.22) μs, while lifetime of photogenerated charges in device is prolonged from 10.00 (±2.38) to 12.23 (±1.86) μs, which helps to upgrade power μconversion efficiency from 9.38 (±1.28)% to 11.42 (±0.80)% (optimized at 12.44%). The efficiency is further upgraded to 14.04% after modifying the carbon electrode with octylammonium iodide. Such efficiency catches up with 85% of that of high‐temperature meso‐CPSCs (prepared at 450 °C) when using (5‐AVA)x(MA)1−xPbI3 as light absorber. The study paves the way to further upgrade the efficiency of the low‐temperature meso‐CPSCs.

Molecular Symmetry of Small-Molecule Passivating Agents Improves Crystal Quality of Perovskite Solar Cells.

Direct interaction with the defect sites of perovskite, functional groups have become the focal point of attention as passivating agents. However, the molecular parent nucleus determines the overall physical properties of the molecule, including the push-pull electronic characteristics of the functional groups, which poses significant challenges in terms of selectivity. Here, we discovered that the binary acid structure based on thiophene as the parent nucleus, due to changes in molecular symmetry, caused significant changes in the molecular dipole moment, resulting in significant changes in the passivation effects on under-coordinated Pb2+ in perovskite solar cells. For the axially symmetric thiophen-2,5-dicarboxylic acid (TPDC), the high dipole moment formed a concentrated surface negative potential on the carboxyl group, showing significant superiority over the centrally symmetric thieno[3,2-b] thiophene-2,5-dicarboxylic acid (TTDC) in forming high-quality perovskite crystals, suppressing charge recombination, enhancing effective charge transport, and raising internal electric fields. The power conversion efficiencies of the fully printable mesoscopic perovskite solar cells based on TPDC and TTDC were 17.15 % and 14.79 %, respectively, exhibiting important research value in the field of small molecule passivation mechanism research.

Room-Temperature Processed Annealing-Free Printable Carbon-Based Mesoscopic Perovskite Solar Cells with 17.34% Efficiency.

Carbon-based printable mesoscopic perovskite solar cells (MPSCs) have promising commercial development due to the use of easily scalable printing processes and low-cost carbon material electrodes. Simplifying the preparation process of MPSCs will undoubtedly contribute to their practical application. Here, we demonstrate that efficient and stable MPSCs can be prepared at room temperature without annealing by using low boiling point 2-methoxyethanol (2-ME) and strongly coordinated N-methyl-2-pyrrolidone (NMP) as a novel mixed solvent under the synergistic effect of ammonium chloride (NH4Cl). The results show that the 2-ME/NMP mixed solvent can generate an optimized coordination environment so that uniform nucleation and crystallization of perovskites in mesopores can be achieved at room temperature without annealing by forming uniform small-sized colloids in the precursor solution. Moreover, our work for the first time introduces NH4Cl as a crystallization modulator during a room-temperature annealing-free process, effectively regulating the crystallization behavior of perovskite in mesopores and obtaining high-quality perovskites. Finally, MPSCs prepared synergistically by a room-temperature annealing-free process based on a low boiling point 2-ME/NMP mixed solvent and NH4Cl modulator achieved a champion power conversion efficiency of 17.34% while demonstrating excellent long-term air stability for over half a year. This work provides a new approach to simplifying the preparation process of MPSCs and preparing efficient and stable MPSCs through a room-temperature annealing-free process.

Nanoscale Pumping Effect of Perovskite via Supported Bilayer Electron Transport Layer for Efficient Printable Mesoscopic Solar Cells

Recently, enhancing the photovoltaic performance of printable mesoscopic perovskite solar cells (p‐MPSCs) poses a significant challenge, particularly in improving the diffusion of perovskite precursor solutions during device assembly. In this research, effective gap‐driven diffusion of the precursor solution perovskite is successfully achieved, leading to the formation of well‐filled and crystallized perovskite through TiO2 nanorod arrays. By incorporating upper‐layer TiO2 nanoparticles, a bilayer electron transport layer with dual crystal phase is developed, establishing a cascaded energy level structure that exhibits superior capabilities in electron collection and directional transport. The effective suppression of nonradiative recombination and efficient charge transfer result in notable enhancements in both open‐circuit voltage and short‐circuit current density. Consequently, the power conversion efficiency of p‐MPSCs devices based on MAPbI3 γ‐butyrolactone solution increases from 14.32% to 16.07% (highest reported value in the literature is 16.21%). These findings highlight a novel interface engineering approach for the fabrication of high‐performance p‐MPSCs devices.

Infiltration Issues in Printed Mesoporous Carbon Perovskite Solar Cells: A Troubleshooting Guide

Printed mesoscopic carbon perovskite solar cells (CPSCs) represent a potential frontrunner to perovskite commercialisation due to their inherent stability and easily scaled fabrication methods. Devices consist of three screen printed...

Printable Counter Electrode with Metal Nitride as the Conductive Medium for Perovskite Solar Cells.

Perovskite solar cells (PSCs) with a booming high power conversion efficiency (PCE) are on their road toward industrialization. A proper design of the counter electrode (CE) with low cost, high conductivity, chemical stability, and good interface contact with the other functional layer atop the perovskite layer is vital for the overall performance of PSCs. Herein, the application of titanium nitride (TiN) is reported as a conductive medium for the printable CE in hole-conductor-free mesoscopic PSCs. TiN improves the conductivity of the CE and reduces the resistivity from 20 to 10 mΩ∙cm. TiN also improves the wettability of the CE with perovskite and enhances the back interface contact, which promotes charge collection. On the other hand, TiN is chemically stable during processing and undergoes no distinguishable chemical reaction with halide perovskite. Devices with TiN as the conductive media in the CE deliver a champion PCEof 19.01%. This work supplies a considerable choice for the CE design of PSCs toward industrial applications.

Simultaneous Enhancement of Efficiency and Operational-Stability of Mesoscopic Perovskite Solar Cells via Interfacial Toughening.

The combined effects of compact TiO2 (c-TiO2 ) electron-transport layer (ETL) are investigated without and with mesoscopic TiO2 (m-TiO2 ) on top, and without and with an iodine-terminated silane self-assembled monolayer (SAM), on the mechanical behavior, opto-electronic properties, photovoltaic (PV) performance, and operational-stability of solar cells based on metal-halide perovskites (MHPs). The interfacial toughness increases almost threefold in going from c-TiO2 without SAM to m-TiO2 with SAM. This is attributed to the synergistic effect of the m-TiO2 /MHP nanocomposite at the interface and the enhanced adhesion afforded by the iodine-terminated silane SAM. The combination of m-TiO2 and SAM also offers a significant beneficial effect on the photocarriers extraction at the ETL/MHP interface, resulting in perovskite solar cells (PSCs) with power-conversion efficiency (PCE) of over 24% and 20% for 0.1 and 1cm2 active areas, respectively. These PSCs also have exceptionally long operational-stability lives: extrapolated T80 (duration at 80% initial PCE retained) is ≈18000 and 10000h for 0.1 and 1cm2 active areas, respectively. Postmortem characterization and analyses of the operational-stability-tested PSCs are performed to elucidate the possible mechanisms responsible for the long operational-stability.

Additive enhanced passivation and lead immobilization of waste expandable polystyrene for perovskite photovoltaics

Every year, millions of tons of expandable polystyrene (EPS) are released into the environment, posing significant environmental pressure due to its slow natural decomposition that takes hundreds of years. Current recycling methods for EPS include organic solvent dissolution and recycling, composite material preparation, and building decoration. However, these methods are costly and have low utilization value. In this study, we propose an innovative approach by incorporating waste EPS into the assembly process of printable mesoscopic perovskite solar cells (p-MPSCs). Our findings reveal that EPS can not only utilize its uncoordinated Pb2+ coordination through the large π bond of the benzene ring, but also the functional groups of C=O and C≡N in its additives, benzophenone peroxide and azobisisobutyronitrile, respectively, play an efficient role in passivating lead defects. Furthermore, EPS effectively acts as a moisture barrier, preventing moisture from entering the interior of the device. This significantly improves device stability and immobilizes lead ions, preventing lead leakage. Our approach not only provides an efficient and environmentally friendly method to recycle EPS, but also offers new solutions to address fundamental scientific challenges in perovskite solar cells, such as lead leakage and stability issues.

Stabilizing perovskite precursors with the reductive natural amino acid for printable mesoscopic perovskite solar cells

Solution processability significantly advances the development of highly-efficient perovskite solar cells. However, the precursor solution tends to undergo irreversible degradation reactions, impairing the device performance and reproducibility. Here, we utilize a reductive natural amino acid, N-acetylcysteine (NALC), to stabilize the precursor solution for printable carbon-based hole-conductor-free mesoscopic perovskite solar cells. We find that I2 can be generated in the aged solution containing methylammonium iodide (MAI) in an inert atmosphere and speed up the MA-FA+ (formamidinium) reaction which produces large-size cations and hinders the formation of perovskite phase. NALC effectively stabilizes the precursor via its sulfhydryl group which reduces I2 back to I− and provides H+. The NALC-stabilized precursor which is aged for 1440 h leads to devices with a power conversion efficiency equivalent to 98% of that for devices prepared with the fresh precursor. Furthermore, NALC improves the device power conversion efficiency from 16.16% to 18.41% along with enhanced stability under atmospheric conditions by modifying grain boundaries in perovskite films and reducing associated defects.

Dendritic growth lowers carbon electrode work function for efficient perovskite solar cells

A major challenge in the development of printable mesoscopic perovskite solar cells (p-MPSCs) is the modification of the carbon electrode's work function to facilitate holes extraction and transport in carbon-based hole transport layer (HTL)-free devices. To address this, we present an innovative approach: in-situ polymerization of aniline on nano-graphite's surface, followed by carbonization, forming a dendritic structure. The modified carbon electrode exhibits reduced work function from −5.06 eV to −5.19 eV and improved energy level alignment with perovskite, facilitating charge collection and significantly enhancing hole collection. This results in a photovoltaic conversion efficiency increase from 15.16 % to 18.19 % in p-MPSCs. Furthermore, the modified carbon electrode-based p-MPSCs exhibit exceptional stability, maintaining high power conversion efficiency even after 10,000-h air exposure without encapsulation. Our work presents a vital strategy for improving photovoltaic conversion characteristics and stability of p-MPSCs through carbon electrode interface modification.

Rapid, low-temperature, air plasma sintering of mesoporous titania electron transporting layers in perovskite solar cells

Reducing the sintering temperature and time of mesoporous titanium dioxide (m-TiO2) from the standard thermal approach of baking at 500 °C for 1 h is an important step for employment of mesoscopic perovskite solar cells (PSCs). We present a robust method based on atmospheric pressure ambient air plasma of the diffuse coplanar surface barrier discharge (DCSBD) for sintering of m-TiO2 in 2.5 min at 70 °C. When implemented in PSCs as an electron transport layer an efficiency of (15.8 ± 1.0) % was achieved, which is on the same level as a standard thermal approach. The organic moieties which hinder the perovskite infiltration into the porous structure were removed to a similar extent as the thermal sintering. The approach does not affect the conduction band alignment with the perovskite absorber and an appropriate energy offset is preserved.

Interface Modification Using Li-Doped Hollow Titania Nanospheres for High-Performance Planar Perovskite Solar Cells.

Titania nanospheres have been utilized as building blocks of electron transporting layers (ETLs) for mesoscopic perovskite solar cells (PSCs). Nevertheless, the power conversion efficiencies (PCEs) reported so far for the mesoscopic PSCs containing titania nanospheres are generally lower than those of the state-of-the-art planar PSCs. Here, we have prepared Li-doped hollow titania nanospheres (Li-HTS) through a "cation-exchange" approach and used them for the first time to modify the SnO2 ETL/perovskite interfaces of planar PSCs. The Li-HTS-modified PSC delivered a PCE of 23.28% with a fill factor (FF) of over 80%, which is significantly higher than the PCE of the control device (20.51%). This is the best PCE achieved for PSCs containing titania nanospheres. Moreover, interfacial modification using Li-HTS greatly improves the stability of the PSCs. This work demonstrates the potential of interface modification using inorganic nanostructures for enhancing the efficiency and stability of planar PSCs.