Efficiency

Researchers at South Korea’s Chonnam National University have reported perovskite-organic hybrid tandem solar cells with 23.07% efficiency processed entirely in open air, bringing the technology a step closer to economic viability.

Schematic illustration of the synthesis of all-inorganic perovskite thin films by dynamic hot-air-assisted method. Image from Energy & Environmental Science 

Researchers have largely relied on meticulously engineering the perovskite crystal structure itself for greater resilience. But these delicate handling steps add cost and complexity not suitable for mass production. The team explained that the focus has recently shifted toward all-solution processed solar cells due to their low energy consumption fabrication processes. The team’s innovation, a dynamic hot air deposition technique, simplified the production process by eliminating the need for humidity-controlled environments.

Researchers at Germany’s Fraunhofer ISE have estimated that the practical power conversion efficiency potential of perovskite-silicon tandem solar cells may reach up to 39.5%. In a recent study, the Fraunhofer ISE scientists set out to provide guidelines for future research on perovskite-silicon tandem solar cells by identifying the most significant loss mechanisms at the perovskite/ETL interface, in the series resistance, and in light management.

The team explained that the calculated practical efficiency potential of 39.5% for a perovskite silicon tandem device under standard measurement conditions (STC) can serve as an input for future studies which are required for a better understanding of the full system before the commercialization of tandem solar cell technology can take place.

Researchers from the Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Germany's University of Potsdam and The Chinese University of Hong Kong have addressed an important aspect in the field of perovskite solar cells (PSCs) – the exact role of excess lead iodide content within the perovskite layer. While an optimal amount of excess lead iodide contributes to improved grain boundary passivation and blocking of minority charge carriers, leading to the development of highly efficient PSCs, the photo-stability of PSCs with surplus lead iodide remains a major concern. This concern stems from the catalytic role excess lead iodide can play in the degradation of PSCs under illumination.

The issue often arises during the fabrication of perovskite films using a two-step spin coating method, where the conversion of lead iodide films to perovskite is hindered due to challenges in controlling the reaction between lead iodide films and cationic precursor solutions. Various modifications of the two-step approach are presented in the literature, each aiming to achieve a near full conversion of lead iodide films into perovskite when exposed to cationic precursor solutions.

GCL Photoelectric Materials (GCL Perovskite), a subsidiary of GCL Tech, has announced that it was able to attain a photoelectric conversion efficiency of 18.04% on a perovskite single-junction solar module, with dimensions measuring 1,000mm by 2,000mm. It was reported that this result was officially tested and confirmed by the China National Institute of Metrology.

GCL Perovskite team has been working on achieving this objective of exceeding the anticipated conversion efficiency of 18% for standard-sized perovskite modules, and the team will now focus on conducting research and development for the next-generation perovskite tandem modules.

Researchers of Karlsruhe Institute of Technology (KIT) and of two Helmholtz platforms—Helmholtz Imaging at the German Cancer Research Center (DKFZ) and Helmholtz AI—have found a way to predict the quality of the perovskite layers and consequently that of the resulting solar cells. Using machine learning and new methods in artificial intelligence (AI), it is possible to assess their quality from variations in light emission already in the manufacturing process.

"Manufacturing these high-grade, multi-crystalline thin layers without any deficiencies or holes using low-cost and scalable methods is one of the biggest challenges," says tenure-track professor Ulrich W. Paetzold who conducts research at the Institute of Microstructure Technology and the Light Technology Institute of KIT.

Researchers at Northwestern University and University of Toronto have developed a way to improve the efficiency of inverted perovskite solar cell using a combination of molecules to address different issues. They reported a dual-molecule solution to overcoming losses in efficiency as sunlight is converted to energy. 

By incorporating a molecule to address surface recombination, in which electrons are lost when they are trapped by defects — missing atoms on the surface, with a second molecule to disrupt recombination at the interface between layers, the team achieved a National Renewable Energy Lab (NREL) certified efficiency of 25.1% where earlier approaches reached efficiencies of just 24.09%.

Researchers from Nanjing University and University of Electronic Science and Technology of China have designed an all-perovskite tandem solar cell based on a wide bandgap perovskite top cell relying on a two-dimensional/three-dimensional heterostructure and a narrow bandgap bottom cell.

Schematic of the solar cell structure and the corresponding cross-sectional SEM image of an all-perovskite tandem solar cell. Image from Nature Communications

The research group used a generic 3D-to-2D perovskite conversion approach to fabricate the top cell. They first deposited a lead-halide perovskite (methylammonium lead iodide - MAPbI₃) layer by a hybrid evaporation/solution method and then transformed the layer into a 2D structure via a long-chain ammonium ligand.

Researchers at the Chinese Academy of Sciences (CAS), Peking University and  Soochow University have developed a polycrystalline silicon tunnelling recombination layer for perovskite/tunnel oxide passivating contact (TOPCon) silicon tandem solar cells (TSCs), which has reportedly achieved excellent efficiency and high stability.  

According to the team, previous efforts to increase device efficiency have mainly focused on improving the top sub-cell, leaving much room for improvement. The recombination layer, which serves as the electrical contact between the top and bottom sub-cells, plays a critical role in further efficiency progress. In this study, the researchers developed a polycrystalline silicon (poly-Si) tunnelling recombination layer that was incorporated into a perovskite/TOPCon silicon tandem cell. Through a two-step annealing strategy, the diffusion of boron and phosphorus dopants could be effectively restrained, granting the device excellent passivation and contact performance.

Researchers at Australia's University of Sydney, University of New South Wales, Macquarie University, Germany's Forschungszentrum Jülich, China's Southern University of Science and Technology ans Slovenia's University of Ljubljana have developed a perovskite-silicon solar cell design using a top perovskite PV device with an energy bandgap of 1.67 eV and a self-assembly monolayer based on carbazole. The tandem cell achieved a higher efficiency compared to counterparts without the monolayer and passed the IEC 61215 standard thermal cycling test.

The device is intended for applications as a top cell in perovskite-silicon tandem solar devices, where the upper cells must have a high energy bandgap to achieve output current matching. These top cells, however, suffer from a higher bandgap-voltage offset, due to non-radiative recombination and energetic misalignment between the perovskite and charge-selective layers. To address this issue, the team utilized a self-assembled monolayer (SAM) based on carbazole, which acts as an effective hole-selective layer (HSL). These SAMs were previously utilized in experimental solar cells and are commonly developed through a molecular glue added during processing in order to dramatically improve adhesion between the light-absorbing perovskite layer and the electron transport layer.

Researchers at China's Wuhan University assume that the practical use of all-perovskite tandem solar cells is hampered by the subpar performance and stability issues associated with mixed tin–lead (Sn–Pb) narrow-bandgap perovskite subcells. In their recent study, they focus on these narrow-bandgap subcells and develop an all-in-one doping strategy for them. 

The scientists introduce aspartate hydrochloride (AspCl) into both the bottom poly(3,4-ethylene dioxythiophene)–poly(styrene sulfonate) and bulk perovskite layers, followed by another AspCl posttreatment. They show that a single AspCl additive can effectively passivate defects, reduce Sn⁴⁺ impurities and shift the Fermi energy level.