References of "Gagliardi, Alessio"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailDevice simulation of all-perovskite four-terminal tandem solar cells: towards 33% efficiency
Singh, Ajay UL; Gagliardi, Alessio

in EPJ Photovoltaics (2021), 12(4),

Inorganic–organic hybrid perovskites offer wide optical absorption, long charge carrier diffusion length, and high optical-to-electrical conversion, enabling more than 25% efficiency of single-junction ... [more ▼]

Inorganic–organic hybrid perovskites offer wide optical absorption, long charge carrier diffusion length, and high optical-to-electrical conversion, enabling more than 25% efficiency of single-junction perovskite solar cells. All-perovskite four-terminal (4T) tandem solar cells have gained great attention because of solution-processability and potentially high efficiency without a need for current-matching between subcells. To make the best use of a tandem architecture, the subcell bandgaps and thicknesses must be optimized. This study presents a drift-diffusion simulation model to find optimum device parameters for a 4T tandem cell exceeding 33% of efficiency. Optimized subcell bandgaps and thicknesses, contact workfunctions, charge transport layer doping and perovskite surface modification are investigated for all-perovskite 4T tandem solar cells. Also, using real material and device parameters, the impact of bulk and interface traps is investigated. It is observed that, despite high recombination losses, the 4T device can achieve very high efficiencies for a broad range of bandgap combinations. We obtained the best efficiency for top and bottom cell bandgaps close to 1.55 eV and 0.9 eV, respectively. The optimum thickness of the top and bottom cells are found to be about 250 nm and 450 nm, respectively. Furthermore, we investigated that doping in the hole transport layers in both the subcells can significantly improve tandem cell efficiency. The present study will provide the experimentalists an optimum device with optimized bandgaps, thicknesses, contact workfunctions, perovskite surface modification and doping in subcells, enabling high-efficiency all-perovskite 4T tandem solar cells. [less ▲]

Detailed reference viewed: 61 (3 UL)
Full Text
Peer Reviewed
See detailMethylamine Gas Treatment Affords Improving Semitransparency, Efficiency, and Stability of CH3NH3PbBr3-Based Perovskite Solar Cells
Singh, Ajay UL; Matteocci, Fabio; Zhu, Hongwei et al

in Solar RRL (2021)

High bandgap semitransparent solar cells based on CH3NH3PbBr3 perovskites are attractive for building integration, tandem cells, and electrochemical applications. The lack of control of the CH3NH3PbBr3 ... [more ▼]

High bandgap semitransparent solar cells based on CH3NH3PbBr3 perovskites are attractive for building integration, tandem cells, and electrochemical applications. The lack of control of the CH3NH3PbBr3 perovskite growth limit the exploitation of CH3NH3PbBr3-based perovskite solar cells. Herein, a posttreatment is carried out after the initial CH3NH3PbBr3 crystallization based on methylamine gas that drastically enhances the perovskite quality leading to a highly crystalline film with improved average visible transmittance (AVT) close to 56%. Opaque devices showed outstanding results in terms of open-circuit voltage and power conversion efficiency (PCE) reaching 1.54 V and 9.2%, respectively. These achievements are ascribed to a film with reduced morphological defects and better interface quality and reduced nonradiative pathways. For the first time, the fabrication of semitransparent CH3NH3PbBr3-based solar cells is demonstrated reaching a maximum PCE equal to 7.6%, an AVT of the full stack device of 52%, and an excellent light stability at maximum-power point tracking. [less ▲]

Detailed reference viewed: 51 (4 UL)
Full Text
Peer Reviewed
See detailRole of cation-mediated recombination in perovskite solar cells
Singh, Ajay UL; Kaiser, Waldemar; Gagliardi, Alessio

in Solar Energy Materials and Solar Cells (2021)

The origin of the hysteresis in the current–voltage (J–V) characteristics in perovskite solar cells (PSCs) is one of the most debated topics of recent years. Hysteretic effects are connected with the slow ... [more ▼]

The origin of the hysteresis in the current–voltage (J–V) characteristics in perovskite solar cells (PSCs) is one of the most debated topics of recent years. Hysteretic effects are connected with the slow redistribution of ionic defects during the voltage sweep. Existing literature focuses on the potential screening due to accumulated ions, solely, while neglecting the possibility of charge trapping and subsequent recombination via ions. We investigate the role of cation-mediated recombination of ions using time-dependent drift–diffusion simulations in MAPbI3 PSCs. Slow-moving cations are considered as traps for the electrons. Trapped electrons can subsequently recombine non-radiatively with holes. We analyze the role of the cation-mediated trapping and its parameters (capture coefficient, cation energy, ion mobility) as well as the scan rate on the device performance. For shallow cation energies, a decrease in open-circuit voltage and slight enhancement in hysteresis is observed. Deep cation energies lead to a substantial deterioration of device performance and large hysteresis enhancement. The presented study emphasizes the importance of considering the interaction of ions with charge carriers beyond the simple electrostatic models to improve our understanding of PSCs. [less ▲]

Detailed reference viewed: 52 (6 UL)
Full Text
Peer Reviewed
See detailTuning halide perovskite energy levels
Canil, Laura; Cramer, Tobias; Fraboni, Beatrice et al

in Energy and Environmental Science (2020)

Solar energy is playing a significant role in the development of a world powered by clean energy sources. In this context, halide perovskite solar cells (PSCs) are considered one of the most promising ... [more ▼]

Solar energy is playing a significant role in the development of a world powered by clean energy sources. In this context, halide perovskite solar cells (PSCs) are considered one of the most promising research lines thanks to their high efficiencies and flexibility, combined with an easy and cheap fabrication process. The possibility of combining different materials and compositions is an excellent advantage of PSCs. However, still, a big limit is posed by the need for a proper energy level alignment between the layers of materials comprising devices. Therefore, it is of utmost interest to develop methods allowing to tune the energy levels of the different materials. In semiconductors physics, a common technique to achieve this purpose is to functionalize the surface of the materials with dipolar molecules. Nevertheless, this has been rarely applied to perovskites because of the highly rough surface of the films. In this study, we show that it is possible to use this technique in hybrid organic–inorganic perovskite semiconductors systematically and tune the direction and magnitude of the shift by controlling the deposition process. These findings offer a toolbox to simplify the application of halide perovskites in optoelectronic devices. [less ▲]

Detailed reference viewed: 39 (7 UL)
Full Text
Peer Reviewed
See detailInterface Electrostatics of Solid-State Dye-Sensitized Solar Cells: A Joint Drift-Diffusion and Density Functional Theory Study
Singh, Ajay UL; Radicchi, Eros; Fantacci, Simona et al

in The Journal of Physical Chemistry C (2019)

Dye-sensitized solar cells (DSCs) have gained great attention in recent years due to their low-cost fabrication, flexibility, and high power conversion efficiency. In a DSC, due to interfaces between the ... [more ▼]

Dye-sensitized solar cells (DSCs) have gained great attention in recent years due to their low-cost fabrication, flexibility, and high power conversion efficiency. In a DSC, due to interfaces between the dye and the chargetransport materials, the interface electrostatics becomes a key factor determining the overall performance of the cell. Liquid-electrolyte-based DSCs suffer from low stability, electrolyte leakage, and, in some cases, electrode corrosion. Replacing liquid electrolyte with a solid semiconducting material leads to poor interfacial contacts, hence the interface electrostatics becomes one of the limiting factors. In this work, we present a drift-diffusion and density functional theory (DFT) study of solid-state DSCs to investigate the electrostatics at the TiO2/organic dye/Spiro-OMeTAD interface and its impact on the adsorbed dye energy levels, its absorption spectrum, and the related charge injection. In our three-dimensional drift-diffusion model, we solve a set of drift-diffusion equations coupled to Poisson equation for electrons, holes, doping impurities, and interface traps simultaneously. After that, we use first-principles DFT modeling of dye-sensitized interfaces in the presence of the calculated electric fields. We find that interface traps located below the conduction band edge of mesoporous TiO2 influence the accumulation of photogenerated holes and built-in electric field near the interface. The built-in electric field leads to change in the energetics at the dye/TiO2 interface, leading to poor charge injection from excited dye into TiO2. The simulations were carried out for different electronic trap densities in TiO2 and different doping levels in the Spiro-OMeTAD hole-transport layer. This study helps to a better understanding of the interface electrostatics and its role in the charge injection mechanism of solid-state DSCs. [less ▲]

Detailed reference viewed: 30 (1 UL)
Full Text
Peer Reviewed
See detailEfficiency of all-perovskite two-terminal tandem solar cells: A drift-diffusion study
Singh, Ajay UL; Gagliardi, Alessio

in Solar Energy (2019)

Organic-inorganic (hybrid) perovskite semiconductors offer a wide range of bandgaps, low-cost deposition, and wide optical absorption, making them an ideal candidate for new photovoltaic devices. All ... [more ▼]

Organic-inorganic (hybrid) perovskite semiconductors offer a wide range of bandgaps, low-cost deposition, and wide optical absorption, making them an ideal candidate for new photovoltaic devices. All-perovskite two terminal (2T) tandem solar cells have the potential to achieve high efficiency and at the same time offer costeffective fabrication. In a 2T tandem cell, it is needed to optimize various device parameters such as bandgaps and thicknesses of the subcells, in order to make the best use of the available solar spectrum. In this study, we propose a drift-diffusion (DD) simulation model to optimize the bandgaps and thicknesses of the top and bottom cells in all-perovskite 2T tandem solar cell. Using our simulation model, we investigated the effect of interface and bulk traps, mobility, doping of the charge transport layers and contact workfunctions to the power conversion efficiency. We calculated up to 36.6% efficiency for an ideal device. We found that the traps at the interfaces and in the bulk perovskite films are the most important factor hampering the tandem cell efficiency. We predicted up to 29.8% efficiency for a device with recombination losses. By changing the mobility in the active material of the bottom cell we found that, the mobility plays an important role in determining the optimum thicknesses of the top and the bottom cells. Optimizing cathode workfunctions leads to a 3–4% improvement in the efficiency. Our study will help to understand the role of various factors limiting tandem cell efficiency and ways to optimize the device parameters to ensure the best performing all-perovskite 2T tandem solar cell. [less ▲]

Detailed reference viewed: 37 (2 UL)