Efficiency - Page 28

A team of researchers from China's Tsinghua University, National Center for Nanoscience and Technology and Switzerland's Institute of Computational Physics (ICP) of the ZHAW School of Engineering have proposed a strategy to reduce defects and microstrains in perovskite films through multifunctional additives, achieving a record PCE of 23.6% for single-junction flexible perovskite solar cells (FPSCs).

Flexible perovskite solar cells (FPSCs) prepared on flexible substrates, which possess excellent flexibility and a high power-to-weight ratio, hold promise as a power source for wearable electronic devices, aerospace, and building integrated photovoltaics (BIPVs). Further improving the power conversion efficiency (PCE) and bending resistance of flexible devices is key to promoting their practical application.

Scientists from Kaunas University of Technology and Vilnius University in Lithuania and University of Colorado in the U.S have proposed a method for increasing the stability and performance of perovskite solar cells. The team synthesized a new class of carbazole-based cross-linkable materials, which are resistant to various environmental effects, including strong solvents used in the production of solar cells.

When applied as hole transporting layers, the new materials helped achieve the 16.9% efficiency of the inverted-architecture perovskite cells at the first attempt. It is expected to reach higher efficiency upon optimization.

Researchers at the U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL), in collaboration with scientists from the University of Toledo, the University of Colorado–Boulder, and the University of California–San Diego, have announced a technological breakthrough and constructed a perovskite solar cell with the dual benefits of being both highly efficient and highly stable.

A unique architectural structure enabled the researchers to record a certified stabilized efficiency of 24% under 1-sun illumination, making it the highest reported of its kind. The highly efficient cell also retained 87% of its original efficiency after 2,400 hours of operation at 55 degrees Celsius.

Scientists from China's Huaqiao University and Henan Normal University have developed a controllable moisture treatment for perovskite films that can promote the mass transportation of organic salts. The films were used to fabricate a 0.2 cm² perovskite solar cell that was able to retain 80% of its initial efficiency after 1200 h.

The group investigated the effects of moisture in the air on the intermediate and final perovskite films in solar cells and developed the controllable moisture treatment that relies on a series of nitrogen (N₂)-protected characterization techniques.

Researchers at Soochow University, Sichuan University and Empa (Swiss Federal Laboratories for Materials Science and Technology), recently devised a new strategy to create high-quality perovskite absorbers with grains in the micrometer scale and prolonged carrier lifetimes. This new strategy is based on a close-space annealing (CSA) process, a heat-based technique that can be used to change a material's chemical properties.

According to the team, controllable crystallization plays a crucial role in the formation of high-quality perovskites. The researchers reported a universal CSA strategy that increases grain size, enhances crystallinity and prolongs carrier lifetimes in low-bandgap (low-Eg) and wide-bandgap (wide-Eg) perovskite films. The CSA strategy devised by the team is universal, as it can be applied to perovskites with various bandgaps to produce high-quality absorbers with enlarged grains and longer carrier lifetimes. As part of their recent study, the team demonstrated its generalizability by successfully using it to prepare absorbers based on perovskites with different chemical compositions.

Scientists from Taiwan's Industrial Technology Research Institute (ITRI) and National Yang Ming Chaio Tung University recently demonstrated a way to produce high-purity lead-iodide, as a precursor material for a perovskite solar cell. The team used temperature to better control the orientation of crystals, and managed to show much higher efficiencies when the precursor was used to fabricate a perovskite layer and subsequently a working solar cell.

The team worked on the fabrication of lead-iodide (PbI₂), an element used in many of the highest-performing perovskite solar cells produced to date. They built on earlier research that has shown the purity and formation of this material could be a key factor in performance once it is integrated into a solar cell. The group’s recent work demonstrates how the crystalline structure and orientation of PbI₂ have a significant impact on cell performance. The researchers also introduce a simple way to control this using temperature during synthesis. 

Researchers from Ulsan National Institute of Science and Technology (UNIST) have reported the deposition of dense and uniform α-formamidinium lead triiodide (α-FAPbI₃) films using perovskite precursor solutions dissolved in ethanol-based solvent. This addresses the issue of halide perovskites generally not being completely soluble in most non-toxic solvents.

The research team, led by Seok Sang-il, has worked out an ethanol-based perovskite precursor solution by designing a complex compound structure so that perovskites can be dissolved well in ethanol. In their study, the researchers obtained power conversion efficiencies of 24.3% using a TiO₂ electrode, and of 25.1% with a SnO₂ electrode.

Researchers from the University of Pennsylvania’s Andrew M. Rappe's group and Princeton University's Yueh-Lin Loo's group recently examined how the molecular make up of certain perovskites might affect their efficiency and offered a path forward to better solar cells using a simple metric.

“The world currently needs more efficient and cost-effective photovoltaic cells, and 3D hybrid perovskite PVs have taken the world by storm,” says Rappe, a professor in Penn’s Department of Chemistry who also co-directs Penn’s VIPER program. “But they are irreversibly damaged by water, which is a showstopper for practical applications. Inserting organic molecular planes between 2D hybrid perovskite planes is a promising scheme to provide efficient, low-cost, and robust solar cells.”

Researchers from the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) and Chinese Academy of Sciences (CAS) have developed a method for processing formamidinium-based perovskite films, using a unique ammonia treatment to remove pore structures formed during the processing.

Methods and solvents used in processing perovskite films have been extensively studied, but these still require additional processing steps or materials to make perovskite films work. For instance, the extremely promising methylamine gas healing method is only suitable for methylammonium-based perovskite, but is not feasible for the more efficient formamidinium-based perovskite. In order to find solutions to the gas healing of the formamidinium-based perovskite films, the researchers first studied the underlying reactions responsible for the challenges. “We have shown that the degradation of formamidinium-containing perovskites is caused by a reaction between the formamidinium cation and aliphatic amines, producing ammonia,” said WANG Xiao from CAS, the second author of the study.

Scientists at the University of California San Diego, Lawrence Berkeley National Laboratory, Stanford University, Los Alamos National Laboratory, Korea's Yonsei University and Daegu Gyeongbuk Institute of Science and Technology have developed a novel perovskite solar cell, made of a lead-free low-dimensional perovskite material with a superlattice crystal structure. The material exhibits efficient carrier dynamics in three dimensions, and its device orientation can be perpendicular to the electrodes. Materials in this particular class of perovskites have so far only exhibited such dynamics in two dimensions—a perpendicularly orientated solar cell has never been reported.

The team reported that thanks to its specific structure, this new type of superlattice solar cell reaches an efficiency of 12.36%, which is the highest reported for lead-free low-dimensional perovskite solar cells (the previous record holder’s efficiency is 8.82%). The new solar cell also has an unusual open-circuit voltage of 0.967 V, which is higher than the theoretical limit of 0.802 V. Both results have been independently certified.