Photon management to reduce energy loss in perovskite solar cells

An optical study on the enhanced light trapping performance of the perovskite solar cell using nanocone structure

Photon management strategies are crucial to improve the efficiency of perovskite thin film (PTF) solar cell. In this work, a nano-cone (NC) based 2D photonic nanostructure is designed and simulated aiming at achieve superior light trapping performance by introducing strong light scattering and interferences within perovskite active layer. Compared to the planar PTF solar cell, the NC nanostructured device with 45 degrees half apex angle obtains highest short-circuit current density, which improved over 20% from 15.00 mA/cm2 to 18.09 mA/cm2. This work offers an alternative design towards effective light trapping performance using 2D photonic nanostructure for PTF solar cell and could potentially be adopted as the nano-structuring strategy for the future perovskite solar cell industry.

Two-Dimensional Materials for Highly Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) offer low costs and high power conversion efficiency. However, the lack of long-term stability, primarily stemming from the interfacial defects and the susceptible metal electrodes, hinders their practical application. In the past few years, two-dimensional (2D) materials (e.g., graphene and its derivatives, transitional metal dichalcogenides, MXenes, and black phosphorus) have been identified as a promising solution to solving these problems because of their dangling bond-free surfaces, layer-dependent electronic band structures, tunable functional groups, and inherent compactness. Here, recent progress of 2D material toward efficient and stable PSCs is summarized, including its role as both interface materials and electrodes. We discuss their beneficial effects on perovskite growth, energy level alignment, defect passivation, as well as blocking external stimulus. In particular, the unique properties of 2D materials to form van der Waals heterojunction at the bottom interface are emphasized. Finally, perspectives on the further development of PSCs using 2D materials are provided, such as designing high-quality van der Waals heterojunction, enhancing the uniformity and coverage of 2D nanosheets, and developing new 2D materials-based electrodes.

Recent Advances in Carbon Nanotube Utilization in Perovskite Solar Cells: A Review

Due to their exceptional optoelectronic properties, halide perovskites have emerged as prominent materials for the light-absorbing layer in various optoelectronic devices. However, to increase device performance for wider adoption, it is essential to find innovative solutions. One promising solution is incorporating carbon nanotubes (CNTs), which have shown remarkable versatility and efficacy. In these devices, CNTs serve multiple functions, including providing conducting substrates and electrodes and improving charge extraction and transport. The next iteration of photovoltaic devices, metal halide perovskite solar cells (PSCs), holds immense promise. Despite significant progress, achieving optimal efficiency, stability, and affordability simultaneously remains a challenge, and overcoming these obstacles requires the development of novel materials known as CNTs, which, owing to their remarkable electrical, optical, and mechanical properties, have garnered considerable attention as potential materials for highly efficient PSCs. Incorporating CNTs into perovskite solar cells offers versatility, enabling improvements in device performance and longevity while catering to diverse applications. This article provides an in-depth exploration of recent advancements in carbon nanotube technology and its integration into perovskite solar cells, serving as transparent conductive electrodes, charge transporters, interlayers, hole-transporting materials, and back electrodes. Additionally, we highlighted key challenges and offered insights for future enhancements in perovskite solar cells leveraging CNTs.

Benzoic acid inhibits intrinsic ion migration for efficient and stable perovskite solar cells

An efficient perovskite solar cell (PSC) has the following characteristics: (1) large perovskite grain size; (2) small ion migration; (3) low defect density states. Here, benzoic acid was employed as an additive to a perovskite solution to improve the thin film quality. Surprisingly, 1.0%-BA can implement all of these features. Therefore, the power conversion efficiency (PCE) of the champion PSC is 18.05%, which is superior to that of the control device (15.42%). In addition, BA-doped PSC kept 86% of its primary PCE after 30 days (RH: 35%), but the control device only retained 75% under the same conditions. The improvement of its stability is because of the inhibition of the cation migration of perovskite by the addition of BA and the passivation of perovskite defects. The results can acquire a better understanding of the potential applications of small organic molecules in improving the PCE and stability of PSC devices.

New Nanophotonics Approaches for Enhancing the Efficiency and Stability of Perovskite Solar Cells

Over the past decade, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has experienced a remarkable ascent, soaring from 3.8% in 2009 to a remarkable record of 26.1% in 2023. Many recent approaches for improving PSC performance employ nanophotonic technologies, from light harvesting and thermal management to the manipulation of charge carrier dynamics. Plasmonic nanoparticles and arrayed dielectric nanostructures have been applied to tailor the light absorption, scattering, and conversion, as well as the heat dissipation within PSCs to improve their PCE and operational stability. In this review, it is begin with a concise introduction to define the realm of nanophotonics by focusing on the nanoscale interactions between light and surface plasmons or dielectric photonic structures. Prevailing strategies that utilize resonance-enhanced light-matter interactions for boosting the PCE and stability of PSCs from light trapping, carrier transportation, and thermal management perspectives are then elaborated, and the resultant practical applications, such as semitransparent photovoltaics, colored PSCs, and smart perovskite windows are discussed. Finally, the state-of-the-art nanophotonic paradigms in PSCs are reviewed, and the benefits of these approaches in improving the aesthetic effects and energy-saving character of PSC-integrated buildings are highlighted.

Synergetic Near- and Far-Field Plasmonic Effects for Optimal All-Perovskite Tandem Solar Cells with Maximized Infrared Absorption

The efficiency and reliability of perovskite solar cells have rapidly increased in conjunction with the proposition of advanced single-junction and multi-junction designs that allow light harvesting to be maximized. However, Sn-based compositions required for optimized all-perovskite tandem devices have reduced absorption coefficients, as opposed to pure Pb perovskites. To overcome this, we investigate near- and far-field plasmonic effects to locally enhance the light absorption of infrared photons. Through optimization of the metal type, particle size, and volume concentration, we maximize effective light harvesting while minimizing parasitic absorption in all-perovskite tandem devices. Interestingly, incorporating 240 nm silver particles into the Pb-Sn perovskite layer with a volume concentration of 3.1% indicates an absolute power conversion efficiency enhancement of 2% in the tandem system. We present a promising avenue for experimentalists to realize ultrathin all-perovskite tandem devices with optimized charge carrier collection, diminishing the weight and the use of Pb.

Synchronous Regulation Strategy of Pyrrolidinium Thiocyanate Enables Efficient Perovskite Solar Cells and Self-Powered Photodetectors

Developing inventive approaches to control crystallization and suppress trap defects in perovskite films is crucial for achieving efficient perovskite photovoltaics. Here, a synchronous regulation strategy is developed that involves the infusion of a zwitterionic ionic liquid additive, pyrrolidinium thiocyanate (PySCN), into the perovskite precursor to optimize the subsequent crystallization and defects. PySCN modification not only orchestrates the crystallization process but also deftly addresses trap defects in perovskite films. Within this, SCN- compensates for positively charged defects, while Py+ plays the role of passivating negatively charged defects. Based on the vacuum flash evaporation without anti-solvent, the air-processed perovskite solar cells (PSCs) with PySCN modification can achieve an extraordinary champion efficiency of 22.46% (0.1 cm2 ) and 21.15% (1.0 cm2 ) with exceptional stability surpassing 1200 h. Further, the self-powered photodetector goes above and beyond, showcasing an ultra-low dark current of 2.13 × 10-10 A·cm-2 , a specific detection rate of 6.12 × 1013  Jones, and an expansive linear dynamic range reaching an astonishing 122.49 dB. PySCN modification not only signifies high efficiency but also ushers in a new era for crystallization regulation, promising a transformative impact on the optoelectronic performance of perovskite-based devices.

Rationally Tailoring Chiral Molecules to Minimize Interfacial Energy Loss Enables Efficient and Stable Perovskite Solar Cells Using Vacuum Flash Technology

Facing the defects and energy barrier at the interface of perovskite solar cells, we propose a chiral molecule engineering strategy to simultaneously heal interfacial defects and regulate interfacial energy band alignment. S-ibuprofen (S-IBU), R-ibuprofen (R-IBU), and racemic ibuprofen (rac-IBU) are used to post-treat perovskite films. rac-IBU molecules possess the strongest anchoring on the surface of perovskites among all chiral molecules, translating into the best defect passivation effect. The hydrophobic isobutyl group and benzene ring could increase the film moisture resistance ability. Due to reduced interfacial defects and interfacial energy barrier, rac-IBU enables efficient devices with a maximum efficiency exceeding 24% based on vacuum flash technology without antisolvents. The encapsulated rac-IBU-modified device could maintain 90% of its initial performance after 1040 h of continuous maximum power point tracking. This work provides a feasible route to minimize interfacial nonradiative recombination losses by controlling spatial conformation via rational chiral molecule engineering.

Future Research Directions in Perovskite Solar Cells: Exquisite Photon Management and Thermodynamic Phase Stability

As power conversion efficiency (PCE) of perovskite solar cells (PSCs) has rapidly increased up to 25.7% in 2022, a curiosity about the achievable limit of the PCE has prevailed and demands understanding about the underlying fundamentals to step forward. Meanwhile, outstanding long-term stability of PSCs over 1000 h has been reported at operating conditions or under damp heat test with 85 °C/85% relative humidity. Herein comes the question as to whether the phase stability issue of perovskite crystal is completely resolved in the most recent state-of-the-art perovskite film or if it deceives everyone into believing so by significantly slowing the kinetics. On the one hand, the fundamental origins of a discrepancy between reported values and the theoretical limit are thoroughly examined, where the importance of light management is greatly emphasized with the introduction of external luminescence as a key parameter to narrow the gap. On the other hand, the phase stability of a perovskite film is understood from thermodynamic point of view to address viable approaches to lower the Gibbs free energy, distinguishing the kinetically trapped condition from the thermodynamically stable phase.

Design of optimized photonic-structure and analysis of adding a SiO2 layer on the parallel CH3NH3PbI3/CH3NH3SnI3 perovskite solar cells

So far, remarkable achievements have been obtained by optimizing the device architecture and modeling of solar cells is a precious and very effective way to comprehend a better description of the physical mechanisms in solar cells. As a result, this study has inspected two-dimensional simulation of perovskite solar cells (PSCs) to achieve a precise model. The solution which has been employed is based on the finite element method (FEM). First, the periodically light trapping (LT) structure has been replaced with a planar structure. Due to that, the power conversion efficiency (PCE) of PSC was obtained at 14.85%. Then, the effect of adding an SiO2 layer to the LT structure as an anti-reflector layer was investigated. Moreover, increasing the PCE of these types of solar cells, a new structure including a layer of CH3NH3SnI3 as an absorber layer was added to the structure of PSCs in this study, which resulted in 25.63 mA/cm2 short circuit current (Jsc), 0.96 V open circuit voltage (Voc), and 20.48% PCE.

Molecular Synergistic Passivation for Efficient Perovskite Solar Cells and Self-Powered Photodetectors

The interface between the perovskite and electron-transporting material is often treated for defect passivation to improve the photovoltaic performance of devices. A facile 4-Acetamidobenzoic acid (containing an acetamido, a carboxyl, and a benzene ring)-based molecular synergistic passivation (MSP) strategy is developed here to engineer the SnOx /perovskite interface, in which dense SnOx are prepared using an E-beam evaporation technology while the perovskite is deposited with vacuum flash evaporation deposition method. MSP engineering can synergistically passivate defects at the SnOx /perovskite interface by coordinating with Sn4+ and Pb2+ with functional group CO in the acetamido and carboxyl. The optimized solar cell devices can achieve the highest efficiency of 22.51% based on E-Beam deposited SnOx and 23.29% based on solution-processed SnO2 , respectively, accompanied by excellent stability exceeding 3000 h. Further, the self-powered photodetectors exhibit a remarkably low dark current of 5.22 × 10-9  A cm-2 , a response of 0.53 A W-1 at zero bias, a detection limit of 1.3 × 1013  Jones, and a linear dynamic range up to 80.4 dB. This work proposes a molecular synergistic passivation strategy to enhance the efficiency and responsivity of solar cells and self-powered photodetectors.

Taurine as a powerful passivator of perovskite layer for efficient and stable perovskite solar cells

Due to the ionic lattice property and the solution manufacture process of the perovskite light absorbing layer, there are several intrinsic defects (such as vacancies and low coordination Pb²⁺ and I^-) in perovskite films, which cause undesired photon-generated carrier recombination in the perovskite solar cells (PSCs) and seriously affect the power conversion efficiency (PCE) of devices. Defect passivation strategy is one of the most effective ways to eliminate the defects in perovskite films. Herein, a multifunctional Taurine molecule was introduced into CH₃NH₃PbI₃ (MAPbI₃) perovskite precursor solution to passivate the defects. It was found that Taurine with sulfonic acid (-SOOOH) and amino (-NH₂) groups can bind with uncoordinated Pb²⁺ and I^- ions, respectively, which can significantly reduce the defect density and suppress the carrier non-radiative recombination. Under atmospheric environment, non-hole transport layer FTO/TiO₂/perovskite/carbon structure PSCs were prepared. The device with Taurine showed a PCE of 13.19%, which is 17.14% higher than that of the control device (11.26%). With the suppressed defects, the Taurine passivated devices also showed enhanced device stability. The unencapsulated Taurine passivated device stored in ambient air after 720 h (temp. ∼25 °C and RH ∼25%) maintained 58.74% original PCE, while that of the control device was only about 33.98%.

In Situ Encapsulated Moiré Perovskite for Stable Photodetectors with Ultrahigh Polarization Sensitivity

Nanostructures provide a simple, effective, and low-cost route to enhance the light-trapping capability of optoelectronic devices. In recent years, nano-optical structures have been widely used in perovskite optoelectronic devices to greatly enhance the device performance. However, the inherent instability of perovskite materials hinders the practical application of these nanostructured optoelectronic devices. Here, in situ encapsulated moiré lattice perovskite photodetectors (PDs) by two nanograting-structured soft templates with relative rotation angles is fabricated. The confinement growth of the two nanograting templates leads to crystal growth with moiré lattice structure, which improves the light-harvesting ability of the perovskite crystal, thereby improving the device performance. The PD exhibits responsivity to 1026.5 A W^-1 . The Moiré lattice-perovskite-based PD maintained 95% of the initial performance after 223 days. After being continuously sprayed with water moist for 180 min, the performance is maintained at 95.7% of its initial level. The nanograting structure endows the device with high polarization sensitivity of I_max /I_min as high as 9.1.

Progresses and Perspectives of Near-Infrared Emission Materials with "Heavy Metal-Free" Organic Compounds for Electroluminescence

Organic/polymer light-emitting diodes (OLEDs/PLEDs) have attracted a rising number of investigations due to their promising applications for high-resolution fullcolor displays and energy-saving solid-state lightings. Near-infrared (NIR) emitting dyes have gained increasing attention for their potential applications in electroluminescence and optical imaging in optical tele-communication platforms, sensing and medical diagnosis in recent decades. And a growing number of people focus on the "heavy metal-free" NIR electroluminescent materials to gain more design freedom with cost advantage. This review presents recent progresses in conjugated polymers and organic molecules for OLEDs/PLEDs according to their different luminous mechanism and constructing systems. The relationships between the organic fluorophores structures and electroluminescence properties are the main focus of this review. Finally, the approaches to enhance the performance of NIR OLEDs/PLEDs are described briefly. We hope that this review could provide a new perspective for NIR materials and inspire breakthroughs in fundamental research and applications.

Nitrogen-Doped Titanium Dioxide as a Hole Transport Layer for High-Efficiency Formamidinium Perovskite Solar Cells

Perovskite solar cells (PSCs) offer advantages over widely deployed silicon solar cells in terms of ease of fabrication; however, the device is still under rigorous materials optimization for cell performance, stability, and cost. In this work, we explore a version of a PSC by replacing the polymeric hole transport layer (HTL) such as Spiro-OMeTAD, P3HT, and PEDOT: PSS with a more air-stable metal oxide, viz., nitrogen-doped titanium dioxide (TiO₂:N). Numerical simulations on formamidinium (FA)-based PSCs in the FTO/TiO₂/FAPbI₃/Ag configuration have been carried out to depict the behaviour of the HTL as well as the effect of absorber layer thickness (∆t) on photovoltaic parameters. The results show that the cell output increases when the HTL bandgap increases from 2.5 to 3.0 eV. By optimizing the absorber layer thickness and the gradient in defect density (Nt), the device structure considered here can deliver a maximum power conversion efficiency of ~21.38% for a lower HTL bandgap (~2.5 eV) and ~26.99% for a higher HTL bandgap of ~3.0 eV. The results are validated by reproducing the performance of PSCs employing commonly used polymeric HTLs, viz. Spiro-OMeTAD, P3HT, and PEDOT: PSS as well as high power conversion efficiency in the highly crystalline perovskite layer. Therefore, the present study provides high-performing, cost-effective PSCs using TiO₂:N.

Light-Trapping Electrode for the Efficiency Enhancement of Bifacial Perovskite Solar Cells

Antireflection and light-trapping coatings are important parts of photovoltaic architectures, which enable the reduction of parasitic optical losses, and therefore increase the power conversion efficiency (PCE). Here, we propose a novel approach to enhance the efficiency of perovskite solar cells using a light-trapping electrode (LTE) with non-reciprocal optical transmission, consisting of a perforated metal film covered with a densely packed array of nanospheres. Our LTE combines charge collection and light trapping, and it can replace classical transparent conducting oxides (TCOs) such as ITO or FTO, providing better optical transmission and conductivity. One of the most promising applications of our original LTE is the optimization of efficient bifacial perovskite solar cells. We demonstrate that with our LTE, the short-circuit current density and fill factor are improved for both front and back illumination of the solar cells. Thus, we observe an 11% improvement in the light absorption for the monofacial PSCs, and a 15% for the bifacial PSCs. The best theoretical results of efficiency for our PSCs are 27.9% (monofacial) and 33.4% (bifacial). Our study opens new prospects for the further efficiency enhancement for perovskite solar cells.

Multifunctional Two-Dimensional Benzodifuran-Based Polymer for Eco-Friendly Perovskite Solar Cells Featuring High Stability

Perovskite solar cells (PSCs) have been regarded as an exceptional renewable energy conversion technology due to their rapidly increasing photovoltaic efficiency, while their practical application is highly retarded by their intrinsic instability and potential lead ion leakage. Here, a two-dimensional (2D) π-conjugated benzodifuran-based polymer, PBDFP-Bz, is adopted to modify the perovskite film. Note that PBDFP-Bz could neutralize surface defects, fine-tune interfacial energetics, and hamper moisture ingression into the perovskite film. Therefore, high-quality perovskite films featuring reduced trap state density and enhanced moisture tolerance could be obtained after modification via PBDFP-Bz. Consequently, PBDFP-Bz-modified devices deliver a higher efficiency of 21.73% versus 19.55% of control ones. Meanwhile, PBDFP-Bz-modified devices can preserve 82.7 and 90.8% of their initial efficiency under continuous heating at 85 °C or light soaking for 500 h. However, the corresponding retained values of control devices are only 56.4 and 70.2%, respectively. Moreover, PBDFP-Bz can effectively prevent the leakage of lead ions in modified devices relative to control ones. This work not only reveals that PBDFP-Bz features high potential for fabricating high-performance and robust PSCs but also indicates that 2D π-conjugated benzodifuran-based polymers can endow PSCs with great security for sustainable development without the concern of lead ion leakage.

Photoelectrochemical energy storage materials: design principles and functional devices towards direct solar to electrochemical energy storage

Advanced solar energy utilization technologies have been booming for carbon-neutral and renewable society development. Photovoltaic cells now hold the highest potential for widespread sustainable electricity production and photo(electro)catalytic cells could supply various chemicals. However, both of them require the connection of energy storage devices or matter to compensate for intermittent sunlight, suffering from complicated structures and external energy loss. Newly developed photoelectrochemical energy storage (PES) devices can effectively convert and store solar energy in one two-electrode battery, simplifying the configuration and decreasing the external energy loss. Based on PES materials, the PES devices could realize direct solar-to-electrochemical energy storage, which is fundamentally different from photo(electro)catalytic cells (solar-to-chemical energy conversion) and photovoltaic cells (solar-to-electricity energy conversion). This review summarizes a critically selected overview of advanced PES materials, the key to direct solar to electrochemical energy storage technology, with the focus on the research progress in PES processes and design principles. Based on the specific discussions of the performance metrics, the bottlenecks of PES devices, including low efficiency and deteriorative stability, are also discussed. Finally, several perspectives of potential strategies to overcome the bottlenecks and realize practical photoelectrochemical energy storage devices are presented.

Functionalizing phenethylammonium by methoxy to achieve low-dimensional interface defects passivation for efficient and stable perovskite solar cells

Low dimensional interface passivation has been proved to be an efficient method to lessen the nonradiative recombination loss in perovskite solar cells. To overcome the limitation of Phenethylammonium (PEA⁺) for carrier transport and water molecule intrusion, we developed a modification strategy by functioning the typical PEA⁺with the 4-methoxy to optimize the interface defects and carrier transport performance, thus maximizing the synchronous improvement of device efficiency and stability. Our results indicate that the 2 mg ml^-14-methoxy-phenethylammonium (MeO-PEA⁺) modified device could achieve a best power conversion efficiency of 19.64% with improved shelf-life stability in ambient conditions. The new passivation molecule of MeO-PEA⁺could possess the capability of defect passivation, carrier transfer, and moisture blocking, demonstrating that rationally designed organic components for interface passivation could help to achieve efficient and stable PSCs.