Technical / research - Page 3

The continuous dimensional scaling of semiconductor and logic photoelectric device requires ferroelectrics to possess robust photoelectric activity and switchable polarization at the nanoscale. However, traditional ferroelectrics such as oxide perovskites generally suffer from relatively large bandgap and deteriorated ferroelectricity in ultrathin forms, while the polarization in many transition metal dichalcogenides is related to inter-layer effects, leading to ferroelectricity that only exists in flakes with a certain layer number and particular stacking forms. The associated challenging fabrication and high-cost synthesis of inorganic ferroelectrics currently render mass industrial production of ultrathin ferroelectric semiconductors impossible. 

Now, researchers from the University of Nebraska Lincoln, University of Warwick and Heidelberg University have used (isopentylammonium)₂(ethylammonium)₂Pb₃I₁₀ (PEPI) to develop an organic-inorganic hybrid perovskite nanoflake with low-cost solution synthesis, switchable polarization, a narrow bandgap (1.86 eV to 2.21 eV form bulk to monolayer), and robust photoelectric properties down to the monolayer. The recent work reveals the great potential of 2D hybrid perovskite ferroelectrics as low-cost ferroelectric semiconductors at the nanoscale.

Researchers from the Adolphe Merkle Institute/ University of Fribourg, Université Grenoble Alpes, Forschungsschwerpunkt Organic Electronics & Photovoltaics, Pusan National University, University of Pavia, University of Tübingen, EPFL and Universidad de Antioquia UdeA have developed a novel light-responsive material that enhances the performance and longevity of perovskite solar cells. This innovation could improve the stability of perovskite solar technology and prevent rapid degradation under real-world conditions.

The key innovation is a photochromic compound called SINO, which changes its properties when exposed to light. When integrated into perovskite solar cells, SINO acts as a dynamic protective layer that adapts to changing conditions during operation. This material transforms between two states in response to sunlight, helping to suppress ion migration within the perovskite and facilitate charge extraction.

Researchers from Mexico's Autonomous University of Querétaro recently addressed PSCs' stability and toxicity concerns by exploring chalcogenide perovskites, specifically ABSe₃ (where A = Ca, Ba, and B = Zr, Hf), as alternatives. These materials exhibit excellent optoelectronic properties, superior thermal and structural stability, and a non-toxic composition, making them ideal candidates for efficient, lead-free solar cells. 

The research team investigated the integration of CaZrSe₃, BaZrSe₃, CaHfSe₃ and BaHfSe₃ as absorber layers in solar cells. The scientists optimized their performance using the Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D), a computational tool developed at the University of Ghent. This simulation allowed them to analyze the behavior of these materials under real-world conditions.

Researchers from the University of North Carolina at Chapel Hill and Hong Kong Polytechnic University have addressed the challenges hindering the reception of wide-bandgap (WBG) perovskite solar cells, which are expected to play a key role in next-generation multi-junction solar cells but suffer from large photovoltage loss, poor stability and scalable fabrication in ambient air.

The team incorporated a reductive methylhydrazinium cation into WBG perovskites, which not only reduced defect density but also suppressed iodide oxidation and halide demixing, enabling scalable fabrication of efficient and stable WBG solar cells and modules in ambient air. 

Inverted perovskite solar cells without pre-depositing a layer of hole-transport materials (HTL-free PSCs) are promising, yet currently suffer from non-irradiative recombination at the perovskite/electron-transport layer (ETL) interface. Recently, researchers from China's  Southern University of Science and Technology (SUSTech) and University of Macau reported a molecular complementary passivation (MCP) strategy by employing propylphosphonic acid 3-ammonium bromide (PPAABr) to cooperate with phenethylammonium bromide (PEABr) to mutually passivate surface defects of I and formamidinium (FA) vacancies by multi-coordination. 

This passivation led to an obvious decrease in interfacial defect-state density and greatly improved exciton and carrier lifetime for the perovskite film. Moreover, MCP surface treatment pushes the perovskite surface Fermi level closer to that of ETL, thereby enhancing interfacial electron extraction. As a result, MCP-based HTL-free PSC achieved a record efficiency of 26.40% (25.92% certified). The encapsulated device retained 94.8% of its initial efficiency after 1,000 h of light soaking. The generality of the MCP strategy also generated a competitive efficiency of 23.66% for 1.68 eV wide-band-gap PSCs.

Researchers from the Indian Institute of Technology Roorkee, CSIR-National Physical Laboratory and Academy of Scientific and Innovative Research (AcSIR) have designed a solution-based fabrication approach involving a high-performance semi-transparent perovskite cell (ST-PSC) stacked in tandem with a hybrid heterojunction silicon solar cell (HHSC). 

The hybrid heterojunction solar cell was embedded as a bottom device in a four-terminal perovskite-silicon solar cell using the new solution processing technique. The novel cell architecture, according to the team, could be produced at significantly lower costs compared to conventional perovskite-silicon tandem designs.

Researchers from the University of Surrey, the National Physical Laboratory and the University of Sheffield have embedded Al₂O₃ nanoparticles, which successfully trapped iodine, to improve the durability of perovskite solar cells (PSCs).

Device architecture of the PSCs used in this study (left) and a photograph of a device (right). Image from: Royal Society of Chemistry

Experiments conducted in extremely hot and humid conditions shown a tenfold increase in performance, lasting more than 1,530 hours as opposed to 160 hours without the alteration. According to the team, by increasing electrical conductivity, decreasing flaws, improving the homogeneity of the perovskite structure, and adding a moisture-resistant layer, the nanoparticles could open the door for more robust and reasonably priced solar technology.

Forming a low-dimensional (LD) capping layer over the surface of three-dimensional (3D) perovskites is a known approach for stabilizing perovskite solar cells (PSCs). However, the performance of treated PSCs tends to be limited by inefficient charge transfer across the LD/3D interfaces.

Recently, researchers from China's Nanjing University of Aeronautics and Astronautics and University of Macau developed a 1D capping layer over the perovskite surface via post-treatment with a conjugated quinolinamine (QA) halide salt. In contrast to 2D perovskites, this unique configuration enables charge transfer between inorganic slabs and adjacent QA spacers in the capping layer, resulting in a reduced dielectric confinement effect and enhanced carrier mobility. 

Recently, a University of Louisville team of researchers used nanoparticle inks by Sofab Inks (a U of Louisville spinout) to create PSCs with ~20% PCE on flexible substrates. Their study addresses the solvent scope and perovskite compatibility of acetate-stabilized yttrium-doped SnO₂ (Y:SnO₂) dispersions.

Tin oxide (SnO₂) stands out as a compelling electron transport material (ETM) for perovskite solar cells (PSCs), boasting exceptional optoelectronic properties, coupled with low-temperature solution processability, cost-effectiveness, and remarkable stability. However, the widespread application of SnO₂ has been hindered by solvent incompatibilities, limiting its use to devices where it is deposited beneath the perovskite layer. To unlock the full potential of SnO₂ and expand its use across various device structures, including inverted PSCs and tandem devices, innovative deposition strategies will need to be developed. These advancements could pave the way for more efficient and versatile solar cell designs, pushing the field of photovoltaics forward.

The scientists showed that dispersions in several lower alcohols and select polar aprotic solvents can be directly deposited on perovskite using scalable and low-temperature processes. In addition, they are compatible with various perovskite formulations, including those with mixed cations and mixed anions.

Researchers from Singapore's Nanyang Technological University and France's University of Lille (CNRS) have developed a biomass-derived furan-based conjugated polymer, PBDF-DFC, enabling a simplified direct precursor integration fabrication method for hybrid perovskite solar cells (HPSCs). 

Unlike traditional thiophene-based polymers, PBDF-DFC reportedly exhibits high solubility in perovskite precursor solvents, allowing direct incorporation into the precursor solution. This direct precursor integration approach could significantly streamline the fabrication process, reducing steps and potentially lowering production costs.