17 research outputs found
Defect Passivation in Lead-Halide Perovskite Nanocrystals and Thin Films: Toward Efficient LEDs and Solar Cells.
Funder: Xunta de Galicia; Id: http://dx.doi.org/10.13039/501100010801Lead-halide perovskites (LHPs), in the form of both colloidal nanocrystals (NCs) and thin films, have emerged over the past decade as leading candidates for next-generation, efficient light-emitting diodes (LEDs) and solar cells. Owing to their high photoluminescence quantum yields (PLQYs), LHPs efficiently convert injected charge carriers into light and vice versa. However, despite the defect-tolerance of LHPs, defects at the surface of colloidal NCs and grain boundaries in thin films play a critical role in charge-carrier transport and nonradiative recombination, which lowers the PLQYs, device efficiency, and stability. Therefore, understanding the defects that play a key role in limiting performance, and developing effective passivation routes are critical for achieving advances in performance. This Review presents the current understanding of defects in halide perovskites and their influence on the optical and charge-carrier transport properties. Passivation strategies toward improving the efficiencies of perovskite-based LEDs and solar cells are also discussed
Laminated Perovskite Photovoltaics: Enabling Novel Layer Combinations and Device Architectures
Highāefficiency perovskiteābased solar cells can be fabricated via either solutionāprocessing or vacuumābased thināfilm deposition. However, both approaches limit the choice of materials and the accessible device architectures, due to solvent incompatibilities or possible layer damage by vacuum techniques. To overcome these limitations, the lamination of two independently processed halfāstacks of the perovskite solar cell is presented in this work. By laminating the two halfāstacks at an elevated temperature (ā90 Ā°C) and pressure (ā50 MPa), the polycrystalline perovskite thināfilm recrystallizes and the perovskite/charge transport layer (CTL) interface forms an intimate electrical contact. The laminated perovskite solar cells with tin oxide and nickel oxide as CTLs exhibit power conversion efficiencies of up to 14.6%. Moreover, they demonstrate longāterm and highātemperature stability at temperatures of up to 80 Ā°C. This freedom of design is expected to access both novel device architectures and pairs of CTLs that remain usually inaccessible
Optimization of SnO electron transport layer for efficient planar perovskite solar cells with very low hysteresisā
Nanostructured tin oxide (SnO) is a very promising electron transport layer (ETL) for perovskite solar cells (PSCs) that allows low-temperature processing in the planar nāiāp architecture. However, minimizing currentāvoltage (JāV) hysteresis and optimizing charge extraction for PSCs in this architecture remains a challenge. In response to this, we study and optimize different types of single- and bilayer SnO ETLs. Detailed characterization of the optoelectronic properties reveals that a bilayer ETL composed of lithium (Li)-doped compact SnO (c(Li)-SnO) at the bottom and potassium-capped SnO nanoparticle layers (NP-SnO) at the top enhances the electron extraction and charge transport properties of PSCs and reduces the degree of ion migration. This results in an improved PCE and a strongly reduced JāV hysteresis for PSCs with a bilayer c(Li)-NP-SnO ETL as compared to reference PSCs with a single-layer or undoped bilayer ETL. The champion PSC with c(Li)-NP-SnO ETL shows a high stabilized PCE of up to 18.5% compared to 15.7%, 12.5% and 16.3% for PSCs with c-SnO, c(Li)-SnO and c-NP-SnO as ETL, respectively
One-Step Thermal Gradient- and Antisolvent-Free Crystallization of All-Inorganic Perovskites for Highly Efficient and Thermally Stable Solar Cells.
Defect Passivation of Perovskite Films for Highly Efficient and Stable Solar Cells
Perovskite solar cells (PSCs) have been introduced as an attractive photovoltaic technology over the past decade due to their low-cost processing, earth-abundant raw materials, and high power conversion efficiencies (PCEs) of up to 25.2%. However, the relatively high density of defects within the bulk, grain boundaries, and surface of polycrystalline perovskite films acts as recombination centers and facilitates ion migration, lowering the theoretical PCE ceiling, often leading to inferior device stability. Therefore, understanding the defect sources and developing passivation methods are key factors for reaching higher PCEs and stabilities in perovskite photovoltaics. Herein, various passivation methods, including bulk and surface treatment of perovskite films, are explored. In the bulk treatment, the passivating agents should be directly added to the perovskite precursor. However, in the surface treatment method, the surface of perovskite films can be treated by inducing passivating agents during the intermediate phase or after annealing steps, denoted here as in-film or surface posttreatment. In addition, different kinds of passivating agents are categorized based on their functional groups. Finally, the outline directions to minimize the defects in perovskite films are highlighted
Gradated Mixed Hole Transport Layer in a Perovskite Solar Cell: Improving Moisture Stability and Efficiency
We demonstrate a simple and facile way to improve the efficiency and moisture stability of perovskite solar cells using commercially available hole transport materials, 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD) and poly(3-hexylthiophene) (P3HT). The hole transport layer (HTL) composed of mixed spiro-OMeTAD and P3HT exhibited favorable vertical phase separation. The hydrophobic P3HT was more distributed near the surface (the air atmosphere), whereas the hydrophilic spiro-OMeTAD was more distributed near the perovskite layer. This vertical separation resulted in improved moisture stability by effectively blocking moisture in air. In addition, the optimized composition of spiro-OMeTAD and P3HT improved the efficiency of the solar cells by enabling fast intramolecular charge transport. In addition, a suitable energy level alignment facilitated charge transfer. A device fabricated using the mixed HTL exhibited enhanced performance, demonstrating 18.9% power conversion efficiency and improved moisture stability.1111sciescopu
Synthesis of mesoporous functional hematite nanofibrous photoanodes by electrospinning
Iron(III) oxide (hematite, Fe2O3) nanofibers, as visible light-induced photoanode for water oxidation reaction of a water splitting process, were fabricated through electrospinning method followed by calcination treatment. The prepared samples were characterized with scanning electron microscopy, and three-electrode galvanostat/potentiostat for evaluating their photoelectrochemical (PEC) properties. The diameter of the as-spun fibers is about 300nm, and calcinated fibers have diameter less than 110nm with mesoporous structure. Optimized multilayered electrospun -Fe2O3 nanostructure mats showed photocurrent density of 0.53mA/cm(2) under dark and visible illumination conditions at voltage 1.23V and constant intensity (900mW/cm(2)). This photovoltaic performance of nanostructure mats makes it suitable choice for using in the PEC water splitting application as an efficient photoanode. This method, if combined with appropriate flexible conductive substrate, has the potential for producing flexible hematite solar fuel generators. Copyright (c) 2015 John Wiley & Sons, Ltd
Simple Post Annealing-Free Method for Fabricating Uniform, Large Grain-Sized, and Highly Crystalline Perovskite Films
We report a simple post annealing-free (PAF) method for making uniform, large grain-sized, and highly crystalline triple cation perovskite films. In this simple process, a perovskite precursor solution was spin-coated onto a TiO2 mesoporous substrate and as an antisolvent, diethyl ether (DEE) was subsequently dripped onto the film during spinning to produce an intermediate phase (IP) of perovskite film. This IP was immediately immersed into a DEE bath at room temperature for only 1 min in replacement of the conventional post annealing (PA) treatment. The as-prepared PAF film was characterized by X-ray powder diffraction, UV vis absorption spectroscopy, fourier transform infrared spectroscopy, scanning electron microscopy, atomic-force microscopy, and photoluminescence spectroscopy. The overall power conversion efficiency (PCE) of the PAF devices was in the range of 18.8-19.5%, which is comparable with the reported PA devices (17.2-18.1%), mainly due to the J(SC) and the FF values, caused by the high absorption ability and the large crystal size with better surface smoothness in the PAF film. This efficiency is the highest reported for perovskite deposition by PAF methods. This new method enables reducing the device fabrication time at room temperature, which will reduce the cost of manufacturing efficient perovskite solar cells.1115sciescopu
p-Type CuI Islands on TiO2 Electron Transport Layer for a Highly Efficient Planar-Perovskite Solar Cell with Negligible Hysteresis
Compact TiO2 is widely used as an electron transport material in planar-perov-skite solar cells. However, TiO2-based planar-perovskite solar cells exhibit low efficiencies due to intrinsic problems such as the unsuitable conduction band energy and low electron extraction ability of TiO2. Herein, the planar TiO2 electron transport layer (ETL) of perovskite solar cells is modified with ionic salt CuI via a simple one-step spin-coating process. The p-type nature of the CuI islands on the TiO2 surface leads to modification of the TiO2 band alignment, resulting in barrier-free contacts and increased open-circuit voltage. It is found that the polarity of the CuI-modified TiO2 surface can pull electrons to the interface between the perovskite and the TiO2, which improves electron extraction and reduces nonradiative recombination. The CuI solution concentration is varied to control the electron extraction of the modified TiO2 ETL, and the optimized device shows a high efficiency of 19.0%. In addition, the optimized device shows negligible hysteresis, which is believed to be due to the removal of trap sites and effective electron extraction by CuI-modified TiO2. These results demonstrate the hitherto unknown effect of p-type ionic salts on electron transport material.1112sciescopu
Recent Progress in Mixed AāSite Cation Halide Perovskite ThināFilms and Nanocrystals for Solar Cells and LightāEmitting Diodes
Funder: Helmholtz Young Investigator Group FrontrunnerAbstract: Over the past few years, leadāhalide perovskites (LHPs), both in the form of bulk thin films and colloidal nanocrystals (NCs), have revolutionized the field of optoelectronics, emerging at the forefront of nextāgeneration optoelectronics. The power conversion efficiency (PCE) of halide perovskite solar cells has increased from 3.8% to over 25.7% over a short period of time and is very close to the theoretical limit (33.7%). At the same time, the external quantum efficiency (EQE) of perovskite LEDs has surpassed 23% and 20% for green and red emitters, respectively. Despite great progress in device efficiencies, the photoactive phase instability of perovskites is one of the major concerns for the longāterm stability of the devices and is limiting their transition to commercialization. In this regard, researchers have found that the phase stability of LHPs and the reproducibility of the device performance can be improved by Aāsite cation alloying with two or more species, these are named mixed cation (double, triple, or quadruple) perovskites. This review provides a stateāofātheāart overview of different types of mixed Aāsite cation bulk perovskite thin films and colloidal NCs reported in the literature, along with a discussion of their synthesis, properties, and progress in solar cells and LEDs