Progress in Materials Development for the Rapid Efficiency Advancement of Perovskite Solar Cells

Constructing tin oxides Interfacial Layer with Gradient Compositions for Efficient Perovskite/Silicon Tandem Solar Cells with Efficiency Exceeding 28

Atomic layer deposition (ALD) growth of conformal thin SnOx films on perovskite absorbers offers a promising method to improve carrier-selective contacts, enable sputter processing, and prevent humidity ingress toward high-performance tandem perovskite solar cells. However, the interaction between perovskite materials and reactive ALD precursor limits the process parameters of ALD-SnOx film and requires an additional fullerene layer. Here, it demonstrates that reducing the water dose to deposit SnOx can reduce the degradation effect upon the perovskite underlayer while increasing the water dose to promote the oxidization can improve the electrical properties. Accordingly, a SnOx buffer layer with a gradient composition structure is designed, in which the compositionally varying are achieved by gradually increasing the oxygen source during the vapor deposition from the bottom to the top layer. In addition, the gradient SnOx structure with favorable energy funnels significantly enhances carrier extraction, further minimizing its dependence on the fullerene layer. Its broad applicability for different perovskite compositions and various textured morphology is demonstrated. Notably, the design boosts the efficiencies of perovskite/silicon tandem cells (1.0 cm2) on industrially textured Czochralski (CZ) silicon to a certified efficiency of 28.0%.

Hydrogen Bonds in Precursor Solution: The Origin of the Anomalous J–V Curves in Perovskite Solar Cells

Perovskite Solar Cells are a promising solar energy harvesting technology due to their low cost and high-power conversion efficiency. A high-quality perovskite layer is fundamental for a highly efficient perovskite Solar Cell. Utilizing a gas quenching process (GQP) can eliminate the need for toxic, flammable, and expensive anti-solvents in the preparation of perovskite layers. It is a promising candidate technology for large scale preparation of perovskite layers, as it can be easily integrated in a production line by coupling up-scalable techniques. The GQP removes the need for polar solvents in the precursor solution layer by using nitrogen flow, rather than extracting them with non-polar solvents. The crystallization dynamics in this process can be significantly different. In this study, we found that the quality of perovskite crystal from GQP is much more sensitive to Lewis base molecules (LBMs) in the precursor solution than it is in anti-solvents technology. Thus, the processing parameters of the LBMs in anti-solvents technology cannot be directly transferred to the GQP. An XRD and 1H NMR study explains the origin of the S-shaped J–V curves and how these LBMs hinder the reaction between PbI2 and monovelent cations.

Performance enhancement of solar cells based on high photoelectric conversion efficiency of h-BN and metal nanoparticles

In this article, we propose a new type of CdTe thin-film solar cell based on a CdTe/CdS heterojunction. We used the finite difference time domain method to simulate the propagation of electromagnetic waves in the time domain under certain boundary conditions and the change in the absorption rate of cells when optimising the structure. The simulation shows that the light absorption rate of the cell is significantly enhanced after adding h-BN and metal particles to the proposed structure. Under the irradiation of standard light AM1.5 with the wavelength range of 300 nm to 1000 nm, presenting a 90% absorption bandwidth over 700 nm, and the average absorption rate is as high as 92.9%. The short-circuit current and open-circuit voltage are 30.98 mA/cm² and 1.155 V, respectively, and the photoelectric conversion efficiency (PCE) increases to 30.76%, which is an increase of 27.58% compared to the original PCE. The result shows that, after metal nanoparticles are embedded in the absorption layer of the cell, the free electrons on the surface of the metal particles oscillate under the action of light. The electromagnetic field is confined to a small area on the surface of the particles and is enhanced, which is beneficial for the absorption of light by the cells. This study provides a basis for theoretical research and feasible solutions for the manufacture of thin-film solar cells with a high absorption rate and high efficiency.

Application of Perovskite Quantum Dots as Absorber for Perovskite Solar Cell

Perovskite quantum dots (QDs) preserve the attractive properties of perovskite bulk materials and present additional advantages, owing to their quantum confinement effect, leading to their applicability as an absorber in perovskite solar cells. In this article, the issues and advantages of perovskite QDs are analyzed in terms of purification, device fabrication with perovskite QDs, light absorption, charge transport and stability. In addition, promising strategies to enhance perovskite QDs and QD-based solar cells are elucidated based on exchange chemistry (ion and ligand exchange), passivation engineering (ion and ligand passivation) and structure engineering (conventional/inverted, planar/mesoscopic and dimensionally graded structures). All these discussions will give a clue to the further development of perovskite QDs and thus the advancement of QD-based solar cells.

Stable Perovskite Solar Cells Using Molecularly Engineered Functionalized Oligothiophenes as Low-Cost Hole-Transporting Materials

Triarylamine-substituted bithiophene (BT-4D), terthiophene (TT-4D), and quarterthiophene (QT-4D) small molecules are synthesized and used as low-cost hole-transporting materials (HTMs) for perovskite solar cells (PSCs). The optoelectronic, electrochemical, and thermal properties of the compounds are investigated systematically. The BT-4D, TT-4D, and QT-4D compounds exhibit thermal decomposition temperature over 400 °C. The n-i-p configured perovskite solar cells (PSCs) fabricated with BT-4D as HTM show the maximum power conversion efficiency (PCE) of 19.34% owing to its better hole-extracting properties and film formation compared to TT-4D and QT-4D, which exhibit PCE of 17% and 16%, respectively. Importantly, PSCs using BT-4D demonstrate exceptional stability by retaining 98% of its initial PCE after 1186 h of continuous 1 sun illumination. The remarkable long-term stability and facile synthetic procedure of BT-4D show a great promise for efficient, stable, and low-cost HTMs for PSCs for commercial applications.

Inclusion of 2D Transition Metal Dichalcogenides in Perovskite Inks and Their Influence on Solar Cell Performance

Organic–inorganic hybrid perovskite materials have raised great interest in recent years due to their excellent optoelectronic properties, which promise stunning improvements in photovoltaic technologies. Moreover, two-dimensional layered materials such as graphene, its derivatives, and transition metal dichalcogenides have been extensively investigated for a wide range of electronic and optoelectronic applications and have recently shown a synergistic effect in combination with hybrid perovskite materials. Here, we report on the inclusion of liquid-phase exfoliated molybdenum disulfide nanosheets into different perovskite precursor solutions, exploring their influence on final device performance. We compared the effect of such additives upon the growth of diverse perovskites, namely CH₃NH₃PbI₃ (MAPbI₃) and triple-cation with mixed halides Cs_x (MA_0.17FA_0.83)_(1−x)Pb (I_0.83Br_0.17)₃ perovskite. We show how for the referential MAPbI₃ materials the addition of the MoS₂ additive leads to the formation of larger, highly crystalline grains, which result in a remarkable 15% relative improvement in power conversion efficiency. On the other hand, for the mixed cation–halide perovskite no improvements were observed, confirming that the nucleation process for the two materials is differently influenced by the presence of MoS₂.

Solvent Engineering as a Vehicle for High Quality Thin Films of Perovskites and Their Device Fabrication

Organic-inorganic halide perovskite solar cells (PSCs) have shown a significant growth in power conversion efficiencies (PCEs) during last decade. Progress in device architecture and high-quality perovskite film fabrication has led to an incredible efficiency over 25% in close to a decade. Developments in solution-based thin film deposition techniques for perovskite layer preparation in PSCs provide low cost and ease of process for their manufacturing, making them a potential contender in future solar energy harvesting technologies. From small area single solar cells to large area perovskite solar modules, solvents play crucial roles in thin film quality and therefore, the device performance and stability. A comprehensive overview of solvent engineering toward achieving the highest qualities for perovskite light absorbing layers with various compositions and based on different fabrication processes is provided in this review. The mechanisms indicating the essential roles a solvent, or a solvent mixture can play to improve the crystallinity, uniformity, coverage and surface roughness of the perovskite films, are discussed. Finally, the role of solvent engineering in transferring from small area laboratory scale PSC fabrication to large area perovskite film deposition processes is explored.

2D Perovskite Nanosheets with Intrinsic Chirality

Chiral perovskite materials have been intensively studied because of their unique properties and wide range of potential applications; however, the synthesis of perovskite nanocrystals with improved chirality has been scarcely investigated. In this Letter, two-dimensional perovskite nanosheets with intrinsic chirality are demonstrated. Inserting chiral amines into the perovskite framework leads to the chirality transfer from amine molecules to perovskite structure. The protecting agent, specifically, achiral octylamine, is found to influence the chiral optical signal or dissymmetric factor of nanosheets significantly. By controlling the amount of octylamine, we have synthesized perovskite nanosheets with the highest g-factor ever reported. We expect our primary demonstration could attract more attention toward the synthesis of intrinsic chiral perovskite nanocrystals and the development of nanocrystal-based chiral-optical devices with improved functions.

Synergetic Effect of Plasmonic Gold Nanorods and MgO for Perovskite Solar Cells

We report new structured perovskite solar cells (PSCs) using solution-processed TiO₂/Au nanorods/MgO composite electron transport layers (ETLs). The proposed method is facile, convenient, and effective. Briefly, Au nanorods (NRs) were prepared and introduced into mesoporous TiO₂ ETLs. Then, thin MgO overlayers were grown on the Au NRs modified ETLs by wet spinning and pyrolysis of the magnesium salt. By simultaneous use of Au NRs and MgO, the power conversion efficiency of the PSC device increases from 14.7% to 17.4%, displaying over 18.3% enhancement, compared with the reference device without modification. Due to longitudinal plasmon resonances (LPRs) of gold nanorods, the embedded Au NRs exhibit the ability to significantly enhance the near-field and far-field (plasmonic scattering), increase the optical path length of incident photons in the device, and as a consequence, notably improve external quantum efficiency (EQE) at wavelengths above 600 nm and power conversion efficiency (PCE) of PSC solar cells. Meanwhile, the thin MgO overlayer also contributes to enhanced performance by reducing charge recombination in the solar cell. Theoretical calculations were carried out to elucidate the PV performance enhancement mechanisms.