Technical / research

The fabrication of perovskite/Si tandem solar cells often encounters the challenge of selecting a suitable sputtering buffer layer (SBL) to prevent damage during the transparent electrode deposition. In their recent work, researchers from China's Northwestern Polytechnical University and Shaanxi Joint Laboratory of Graphene (NPU), Chinese Academy of Sciences and Ningbo New Materials Testing and Evaluation Center Co. developed a perovskite-silicon tandem solar cell that uses an indium oxide sputtering buffer layer to protect the perovskite absorber and the electron transport layer from damages that might occur during the electrode deposition process. The new layer not only granted this protection but also showed strong optical and electrical properties. 

The team introduced the indium oxide (In₂O₃) buffer layer via e-beam deposition to fabricate semi-transparent perovskite solar cells. The optical transmittance and electrical conductivity of In₂O₃ highly depend on the deposition rate. High deposition rate results in high ratio of metallic indium in the film, which causes severe parasitic absorption. A 20 nm-thick In₂O₃ film deposited at lower rate demonstrated high conductivity, transmittance and robust protection during sputtering. 

An international team of researchers, led by the University of Surrey with Imperial College London, recently reported a strategy to improve both the performance and stability for perovskite solar cells by mitigating a previously hidden degradation pathway.

In their new study, the scientists detail how they produced lead-tin perovskite solar cells that reach more than 23% power conversion efficiency (PCE) – which the team says is one of the best results achieved with this material and importantly, a design strategy which improves the lifetime of these devices by 66%. 

Bifacial perovskite solar cells (Bi-PSCs) have attracted substantial attention due to their potential for enhanced power generation, suitability for integration into building structures and applicability in multijunction PV systems. Recently, researchers from the Indian Institute of Technology Bombay reported the fabrication of efficient Bi-PSCs and investigated their unique properties using various characterization techniques, including Lambertian reflection effects through tilt angle arrangements and bottom albedo illuminations. 

The control device achieved a maximum power conversion efficiency (PCE) of 17.46% under front-side 1 Sun AM1.5G illumination. A significant influence of ground Lambertian reflection was observed with tilt angle variations, resulting in an increase in PCE from 17.46% → 18.82% as the tilt angle reached 20°. Additionally, enhancing the rear-side albedo to 0.5 Sun yielded a maximum PCE of 26% with a bifaciality factor of ∼90% at a tilt angle of 20°. 

Chinese Academy of Sciences (CAS) researchers believe that the issue of instability of perovskite solar cells (PSCs) primarily originates from the migration of halide ions—particularly iodide ions (I⁻). Under light exposure and thermal stress, I⁻ migrates and transforms into I₂, leading to irreversible degradation and performance loss. 

To tackle this challenge, the team introduced the additive 2,1,3-benzothiadiazole,5,6-difluoro-4,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) (BT2F-2B) into the perovskite. The strong coordination between the unhybridized p orbital and lone-pair electrons from I⁻ inhibits the deprotonation of MAI/FAI and the subsequent conversion of I⁻ to I₂. The highly electronegative fluorine enhances its electrostatic interaction with I⁻. Consequently, the synergistic effect of BT2F-2B effectively suppresses the decomposition of perovskite and the defect density of the iodide vacancies. 

Researchers from King Abdullah University of Science and Technology (KAUST) set out to develop X-ray detection technology with reduced radiation dosage without compromising detection efficiency. The team developed a cascade-engineered approach that uses two interconnected single-crystal devices to mitigate dark current and enhance the detection limit. 

Using methylammonium lead bromide (MAPbBr₃) perovskite single crystals, the scientists engineered devices that significantly reduced detection thresholds and improved signal-to-noise ratios (SNRs). 

Researchers from Ecole Polytechnique Fédérale de Lausanne (EPFL), North China Electric Power University, Westlake University, Lomonosov Moscow State University and others have described the addition of N,N-dimethylmethyleneiminium chloride ([Dmei]Cl) into perovskite precursor solutions to produce two cations in situ—namely 3-methyl-2,3,4,5-tetrahydro-1,3,5-triazin-1-ium ([MTTZ]⁺) and dimethylammonium ([DMA]⁺) cations - that enhanced the photovoltaic
performance and stability of perovskite solar modules.  

A schematic of the roles of [MTTZ]⁺ and [DMA]⁺ in the 3D perovskite matrix. Image from: Science

The team explained that the in situ formation of [MTTZ]⁺ cation increased the formation energy of iodine vacancies and enhanced the migration energy barrier of iodide and cesium ions, which suppressed nonradiative recombination, thermal decomposition, and phase segregation processes. 

The formation of a homogeneous passivation layer based on phase-pure two-dimensional (2D) perovskites is a challenge for perovskite solar cells, especially when upscaling the devices to modules. Researchers from China's Wuhan University of Technology, Xidian University, University of Electronic Science and Technology of China and Germany's Technical University of Munich have revealed a chain-length-dependent and halide-related phase separation problem of 2D perovskite growing on top of three-dimensional perovskites. 

The scientists have demonstrated that a homogeneous 2D perovskite passivation layer can be formed upon treatment of the perovskite layer with formamidinium bromide in long-chain ( >10) alkylamine ligand salts. 

Researchers from Zhejiang University, Soochow University, King Abdullah University of Science and Technology (KAUST), The Hong Kong Polytechnic University and Suzhou Maxwell Technologies have addressed common challenges related to hole transport layers that are commonly used for the perovskite top cells, such as defects, non-conformal deposition or de-wetting of the overlying perovskite on the textured silicon bottom cells.

The team decided to develop a strategy based on co-deposition of copper(I) thiocyanate and perovskite, where effective perovskite grain boundary passivation and efficient hole collection are simultaneously achieved by the embedded copper(I) thiocyanate, which creates local hole-collecting contacts. Fabricated monolithic perovskite/silicon tandem devices achieved a certified power conversion efficiency of 31.46% for 1 cm² area devices. 

A Research Group led by Prof. Eva Unger at Helmholtz Zentrum Berlin (HZB), in collaboration with the Indian Institute of Technology Bombay and University of Jammu, has reported the use of inkjet printing to fabricate thin films of combinatorial mixed formamidinium tin-lead perovskites and evaluated their layer quality and device performance. The team focused on optimizing the inkjet-printing process to ensure precise film deposition and enhance device performance.

Image credit: ACS Applied Materials and Interfaces

The scientists deposited Sn/Pb intermixed FASn_1–xPb_xI₃ (x = 0.25, 0.5, and 0.75)-based perovskite thin films through inkjet printing. The study focused on finding the ideal composition ratio for a favorable photovoltaic performance. The deposited FASn_1–xPb_xI₃ thin films were subjected to various characterizations followed by their implementation in solar cells. 

The certified efficiency of 1 cm² scale all-perovskite tandem solar cells tends to lag behind that of their small-area (~0.1 cm2) counterparts. This performance deficit originates from inhomogeneity in wide-bandgap (WBG) perovskite solar cells (PSCs) at a large scale. The inhomogeneity is thought to be introduced at the bottom interface and within the perovskite bulk itself. 

Researchers from Nanjing University, Jilin University, University of Cambridge, University of Victoria, The Australian National University, Chinese Academy of Sciences (CAS) and Renshine Solar (Suzhou) have reported an all-perovskite tandem solar cell based on a wide-bandgap top perovskite cell with a 20.5% efficiency.