Organo-halide Perovskite Solar Cells Research Articles

Stability improvement of perovskite solar cell using photoswitchable and moisture resistant dual-function interfacial layer

Although the power conversion efficiency of organo-halide perovskite solar cells (PSCs) has reached up to 25.5%, they face challenges to their commercialization due to the lack of stability against moisture, light, and heat. In this work, the durability of the PSC is improved using an efficient interfacial layer that simultaneously protects the perovskite layer against moisture and UV light/heat. The interfacial layer consists of hydrophobic two-dimensional perovskite (2D-PEA2PbI4) and azobenzene phase change material (PCM). The PCM acts as the UV light protector that can efficiently absorb UV light through its isomerization from cis to trans isomer. Remarkably, adding this dual-function interfacial layer prolongs the lifetime of the devices, particularly under one sun illumination and humid atmosphere (65–80% relative humidity). Also, the solid-solid PCM enhances the PCE of devices with 2D-perovskite by the specific orientation of 2D-perovskite between the 3D-perovskite grains. The stability of the modified device has been enhanced almost ten times as compared with the reference device.

Evaluation of Damage Coefficient for Minority-Carrier Diffusion Length of Triple-Cation Perovskite Solar Cells under 1 MeV Electron Irradiation for Space Applications

Organo-halide perovskite solar cells (PSCs) are lightweight and low cost, and they offer high power conversion efficiencies. PSCs have proven to be useful in terrestrial applications. In addition, they are particularly attractive for space applications because they can offer a higher radiation tolerance than GaAs and Si solar cells. This paper evaluates the damage coefficient for minority-carrier diffusion length KL of perovskite crystals after 1 MeV electron irradiation by time-resolved photoluminescence measurements to investigate the reason for their high radiation tolerance. Results show that perovskite crystals have a lower damage coefficient KL than that of InP crystals with a high radiation tolerance. On the other hand, first-principles calculations indicate that the displacement energy of perovskite crystals is as low as that of Si, which does not have a high radiation tolerance. The present results suggest that the annealing effect occurs for PSCs at room temperature.

In-Situ Nano-Auger Probe of Chloride-Ions during CH3NH3PbI3-xClx Perovskite Formation.

Organo-halide perovskite solar cells (PSCs) have emerged as next-generation photovoltaics, owing to their high power-conversion efficiency (PCE), lower production cost, and high flexibility. ABX3-structured methylammonium lead triiodide (CH3NH3PbI3 or MAPbI3) perovskite is a widely studied light-absorbing material in PSCs. Interestingly, a small amount of chlorine incorporation into MAPbI3 increases charge carrier diffusion lengths (from 129 nm to 1069 nm), which enables planar structured PSCs with high PCEs. However, existence of chloride ions in the final perovskite film is still under debate. Contrastingly, few studies reported a negligible amount or absence of chloride ions in the final film, while others reported detection of chloride ions in the final film. Herein, we observed the microstructure and chlorine content of MAPbI3−xClx thin films with increasing temperature via an in-situ nano-Auger spectroscopy and in-situ scanning electron microscopic analysis. The relative precipitation of MAPbI3−xClx films occur at lower temperature and MAPbI3−xClx grains grow faster than those of MAPbI3 grains. Local concentrations of chlorine at intragrain and the vicinity of grain boundary were analyzed to understand the behavior and role of the chloride ions during the microstructural evolution of the MAPbI3−xClx films.

Strain-relaxed tetragonal MAPbI3 results in efficient mesoporous solar cells

In mesoporous organo-halide perovskite solar cells, the coexistence of tetragonal phase and cubic phase in the perovskite layer is found to result in strained crystal structure at the mesoporous TiO 2 (mp-TiO 2 )/perovskite heterointerface. This results in structural defects pinholes, grain boundaries, and interfacial porosity which is detrimental towards photovoltaic performance and device stability. The strain at the interface originates from the lattice mismatch between the mp-TiO 2 nanoparticles (NPs) and perovskite. Here, a transformative approach is demonstrated to realize relaxed and high purity tetragonal phase MAPbI 3 (RP) near the mp-TiO 2 interface region. This approach involves inserting a ~2 nm lattice matched buffer layer of cubic CsPbBr 3 between mp-TiO 2 NPs and MAPbI 3 , which serves as a template for epitaxial growth for top MAPbI 3 . The solar cell with relaxed MAPbI 3 shows a power conversion efficiency (PCE) of 22.12% with significantly enhanced environmental, light, and thermal stability. • Strain engineering is invoked to achieve strain-relaxed and tetragonal MAPbI 3 at the mp-TiO 2 /MAPbI 3 heterointerface. • The modified relaxed MAPbI 3 -based device exhibits a PCE of 22.12%. • The modified devices show enhanced environmental, thermal, and light stabilities.

Core/Shell Nanocrystal Tailored Carrier Dynamics in Hysteresisless Perovskite Solar Cells with ∼20% Efficiency and Long Operational Stability

The ambient stability, hysteresis, and trap states in organo-halide perovskite solar cells (PSCs) are correlated to the influence of interlayer interfaces and grain boundaries. Astute incorporation of Cu2ZnSnS4 (CZTS) and Au/CZTS core/shell nanocrystals (NCs) can realize the goal of simultaneously achieving better performance and ambient stability of the PSCs. With optimized Au/CZTS NC size and concentration in the photoactive layer, power conversion efficiency can be increased up to 19.97 ± 0.6% with ambient air stability >800 h, as compared to 14.46 ± 1.02% for the unmodified devices. Through efficient carrier generation by CZTS and perovskite, accompanied by the plasmonic effect of Au, carrier density is sufficiently increased as validated by transient absorption spectroscopy. NCs facilitate the interfacial charge transfer by suitable band alignment and removal of recombination centers such as metallic Pb0, surface defects, or impurity sites. NC embedding also increases the perovskite grain size and assists in pinhole filling, reducing the trap state density.

Device simulation of perovskite solar cells with molybdenum disulfide as active buffer layer

Organo-halide Perovskite Solar Cells (PSC) have been reported to achieve remarkably high power conversion efficiency (PCE). A thorough understanding of the role of each component in solar cells and their effect as a whole is still required for further improvement in PCE. In this paper, the effect of Molybdenum Disulfide (MoS2) in PSC with mesoporous structure configuration was analyzed using Solar Cell Capacitance Simulator (SCAPS). With the MoS2 layer which having two-fold function, acting as a protective layer, by preventing the formation of shunt contacts between perovskite and Au electrode, and as a hole transport material (HTM) from the perovskite to the Spiro-OMETAD. As simulated, PSC demonstrates a PCE, ŋ of 13.1%, along with stability compared to typical structure of PSC without MoS2 (Δ ŋ/ŋ=-9% vs. Δ ŋ/ŋ=-6%). The results pave the way towards the implementation of MoS2 as a material able to boost shelf life which very useful for new material choice and optimization of HTMs.

Understanding the Influence of Interface Morphology on the Performance of Perovskite Solar Cells.

In recent years, organo-halide perovskite solar cells have garnered a surge of interest due to their high performance and low-cost fabrication processing. Owing to the multilayer architecture of perovskite solar cells, interface not only has a pivotal role to play in performance, but also influences long-term stability. Here we have employed diverse morphologies of electron selective layer (ESL) to elucidate charge extraction behavior in perovskite solar cells. The TiO2 mesoporous structure (three-dimensional) having varied thickness, and nanocolumns (1-dimensional) with tunable length were employed. We found that a TiO2 electron selective layer with thickness of about c.a. 100 nm, irrespective of its microstructure, was optimal for efficient charge extraction. Furthermore, by employing impedance spectroscopy at different excitation wavelengths, we studied the nature of recombination and its dependence on the charge generation profile, and results showed that, irrespective of the wavelength region, the fresh devices do not possess any preferential recombination site, and recombination process is governed by the bulk of the perovskite layer. Moreover, depending on the type of ESL, a different recombination mechanism was observed that influences the final behavior of the devices.

Evidence of Tailoring the Interfacial Chemical Composition in Normal Structure Hybrid Organohalide Perovskites by a Self-Assembled Monolayer.

Current-voltage hysteresis is a major issue for normal architecture organo-halide perovskite solar cells. In this manuscript we reveal a several-angstrom thick methylammonium iodide-rich interface between the perovskite and the metal oxide. Surface functionalization via self-assembled monolayers allowed us to control the composition of the interface monolayer from Pb poor to Pb rich, which, in parallel, suppresses hysteresis in perovskite solar cells. The bulk of the perovskite films is not affected by the interface engineering and remains highly crystalline in the surface-normal direction over the whole film thickness. The subnanometer structural modifications of the buried interface were revealed by X-ray reflectivity, which is most sensitive to monitor changes in the mass density of only several-angstrom thin interfacial layers as a function of substrate functionalization. From Kelvin probe force microscopy study on a solar cell cross section, we further demonstrate local variations of the potential on different electron-transporting layers within a solar cell. On the basis of these findings, we present a unifying model explaining hysteresis in perovskite solar cells, giving an insight into one crucial aspect of hysteresis for the first time and paving way for new strategies in the field of perovskite-based opto-electronic devices.

Current state and perspectives for organo-halide perovskite solar cells: Crystal structures and thin film formation, morphology, processing, degradation, stability improvement by carbon nanotube

The fundamental problems of the modern state of the studies of organic-inorganic organo-halide perovskites (OHP) as basis for high efficiency thin film solar cells are discussed. Perovskite varieties and background properties are introduced. The chronology of development of the studies in this direction has been presented — structural aspects of these OHP perovskites, from early 2D to recent 3D MAPbI3 perovskites and important technological aspects of smooth thin film structure creation by various techniques, such as solvent engineering, spin- and dip-coating, vacuum deposition, cation exchange approach, nanoimprinting (particularly, a many-sided role of polymers). The most important theoretical problems such as electronic structure of lattice, impurity and defect states in pure and mixed perovskites, suppressed electron-hole recombination, extra-long lifetimes, and diffusion lengths are analyzed. Degradation effects associated with moisture and photo irradiation, as well as degradation of metallic electrodes to OHP solar cells have been considered. The application of carbon nanostructures: carbon nanotubes (CNT) and graphene as stable semitransparent charge collectors to OHP perovskites is demonstrated on the example of original results of authors.

Current state and perspectives for organo-halide perovskite solar cells. Part 1. Crystal structures and thin film formation, morphology, processing, degradation, stability improvement by carbon nanotubes. A review

The fundamental problems of the modern state of the studies of organic–inorganic organo-halide perovskites (OHP) as basis for high efficiency thin film solar cells are discussed. Perovskite varieties and background properties are introduced. The chronology of development of the studies in this direction has been presented – structural aspects of these OHP perovskites, from early 2D to recent 3D MAPbI3 perovskites and important technological aspects of smooth thin film structure creation by various techniques, such as solvent engineering, spin- and dip - coating, vacuum deposition, cation exchange approach, nanoimprinting (particularly, a many-sided role of polymers). The most important theoretical problems such as electronic structure of lattice, impurity and defect states in pure and mixed perovskites, suppressed electron-hole recombination, extra-long lifetimes, and diffusion lengths are analyzed. Degradation effects associated with moisture and photo irradiation, as well as degradation of metallic electrodes to OHP solar cells have been considered. The application of carbon nanostructures: carbon nanotubes (CNT) and graphene as stable semitransparent charge collectors to OHP perovskites is demonstrated on the example of original results of authors.

Improved Reproducibility for Perovskite Solar Cells with 1 cm2 Active Area by a Modified Two-Step Process.

With rapid progress in recent years, organohalide perovskite solar cells (PSC) are promising candidates for a new generation of highly efficient thin-film photovoltaic technologies, for which up-scaling is an essential step toward commercialization. In this work, we propose a modified two-step method to deposit the CH3NH3PbI3 (MAPbI3) perovskite film that improves the uniformity, photovoltaic performance, and repeatability of large-area perovskite solar cells. This method is based on the commonly used two-step method, with one additional process involving treating the perovskite film with concentrated methylammonium iodide (MAI) solution. This additional treatment is proved to be helpful for tailoring the residual PbI2 level to an optimal range that is favorable for both optical absorption and inhibition of recombination. Scanning electron microscopy and photoluminescence image analysis further reveal that, compared to the standard two-step and one-step methods, this method is very robust for achieving uniform and pinhole-free large-area films. This is validated by the photovoltaic performance of the prototype devices with an active area of 1 cm2, where we achieved the champion efficiency of ∼14.5% and an average efficiency of ∼13.5%, with excellent reproducibility.

Microwave-synthesized tin oxide nanocrystals for low-temperature solution-processed planar junction organo-halide perovskite solar cells

Tin oxide nanoparticles prepared by microwave-assisted non-aqueous sol–gel were used to cast an electron transporting layer for organohalide perovskite solar cells showing, in average, high efficiencies thanks to the good optoelectronic properties of the material.

Considerations for Upscaling of Organohalide Perovskite Solar Cells

Thin film organohalide lead perovskite‐based solar cells have emerged over the last five years as a potentially low‐cost, low‐embedded‐energy and high‐efficiency photovoltaic technology. However, almost all reported high‐efficiency devices have small active areas significantly less than 1 cm2. Upscaling of organohalide lead perovskite solar cells is now required for successful manufacturing and commercialization. In this work, three generic design rules for large area devices are proposed. Using these design rules, high efficiency large area (2.0 cm2) cells are demonstrated based on a predictive methodology incorporating the optoelectronic design of highly transparent and conductive electrodes, and controlled crystal size and uniformity of the organohalide perovskite junction. These optimized large area monolithic solar cells show power conversion efficiencies (PCEs) >12%, with an enhanced open‐circuit voltage (V oc) of 1.02 V and respectable fill factor (FF) of 0.61.

Mesostructured Fullerene Electrodes for Highly Efficient n–i–p Perovskite Solar Cells

Electron-transporting layers in today’s state-of-the-art n–i–p organohalide perovskite solar cells are almost exclusively made of metal oxides. Here, we demonstrate a novel mesostructured fullerene-based electron-transporting material (ETM) that is crystalline, hydrophobic, and cross-linked, rendering it solvent- and heat-resistant for subsequent perovskite solar cell fabrication. The fullerene ETM is shown to enhance the structural and electronic properties of the CH3NH3PbI3 layer grown atop, reducing its Urbach energy from ∼26 to 21 meV, while also increasing crystallite size and improving texture. The resulting mesostructured n–i–p solar cells achieve reduced recombination, improved device-to-device variation, reduced hysteresis, and a power conversion efficiency above 15%, surpassing the performance of similar devices prepared using mesoporous TiO2 and well above the performance of planar heterojunction devices on amorphous or crystalline [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). This work is...

Unravelling the Effects of Grain Boundary and Chemical Doping on Electron-Hole Recombination in CH3NH3PbI3 Perovskite by Time-Domain Atomistic Simulation.

Advancing organohalide perovskite solar cells requires understanding of carrier dynamics. Electron-hole recombination is a particularly important process because it constitutes a major pathway of energy and current losses. Grain boundaries (GBs) are common in methylammonium lead iodine CH3NH3PbI3 (MAPbI3) perovskite polycrystalline films. First-principles calculations have suggested that GBs have little effect on the recombination; however, experiments defy this prediction. Using nonadiabatic (NA) molecular dynamics combined with time-domain density functional theory, we show that GBs notably accelerate the electron-hole recombination in MAPbI3. First, GBs enhance the electron-phonon NA coupling by localizing and contributing to the electron and hole wave functions and by creating additional phonon modes that couple to the electronic degrees of freedom. Second, GBs decrease the MAPbI3 bandgap, reducing the number of vibrational quanta needed to accommodate the electronic energy loss. Third, the phonon-induced loss of electronic coherence remains largely unchanged and not accelerated, as one may expect from increased electron-phonon coupling. Further, replacing iodines by chlorines at GBs reduces the electron-hole recombination. By pushing the highest occupied molecular orbital (HOMO) density away from the boundary, chlorines restore the NA coupling close to the value observed in pristine MAPbI3. By introducing higher-frequency phonons and increasing fluctuation of the electronic gap, chlorines shorten electronic coherence. Both factors compete successfully with the reduced bandgap relative to pristine MAPbI3 and favor long excited-state lifetimes. The simulations show excellent agreement with experiment and characterize how GBs and chlorine dopants affect electron-hole recombination in perovskite solar cells. The simulations suggest a route to increased photon-to-electron conversion efficiencies through rational GB passivation.

Solvent‐Mediated Dimension Tuning of Semiconducting Oxide Nanostructures as Efficient Charge Extraction Thin Films for Perovskite Solar Cells with Efficiency Exceeding 16%

The recent surge in efficiency and progress of organohalide perovskite solar cells (PSCs) has been significant. The PSC performance is significantly influenced by nanostructuring as this varies the intrinsic optical, electrical, and electrochemical properties. Diverse TiO2 electron transport layers (ETLs) are solvothermally grown on the transparent conducting oxide substrate with different dimensionalities, 0D nanoparticles (TNP), 1D nanowires (TNW) to 2D nanosheets (TNS), by varying the organic solvent used. These layers feature enhanced optical transparency (≈2%–5% transmittance improvement compared to pristine fluorine doped tin oxide, FTO, glass) minimizing light absorption losses. PSCs constructed using 1D TNW or 2D TNS yield enhanced photovoltaic performance compared to the 0D TNP counterparts. This is a result of i) improved infiltration of the perovskite in the porous TNW or TNS network and ii) facilitated electron transport and charge extraction at the TNW/perovskite or TNS/perovskite interfaces, thus reduced interfacial recombination loss. Employing a bilayered ETL film consisting of a self‐assembled TiO2 blocking layer and a subsequent TNW active layer, produces PSC devices with an efficiency exceeding 16%. This bilayered ETL film can simultaneously block the photogenerated holes and enhance electron ­extraction, therefore improving PSC performance.

Efficient, monolithic large area organohalide perovskite solar cells

A generic and simple approach to realize solution processed, monolithic large area perovskite solar cells.

Recent progress of organohalide perovskite solar cells

Since 2009, greater attention has been paid to organic-inorganic hybrid CH3NH3PbI3 solar cells because of their simple fabrication process and high power conversion efficiency. Organohalide perovskite solar cells now develop very fast and their photovoltaic performance has been gradually improved. However, because of a band-gap limitation, the sunlight absorption spectrum of CH3NH3PbI3 is not broad enough to produce enhanced photovoltaic properties. In addition, Pb, as an important element, is toxic in organohalide perovskite. Thus, it is significant and meaningful to fabricate narrow-gap, environmentally friendly organohalide perovskite solar cells with better chemical stability. In the present paper, we mainly reviewed the progress in the band-gap engineering of perovskite materials to identify elements to replace toxic Pb and improve the absorption efficiency of incident light and the photovoltaic performance of solar cells. The influences of organic and inorganic hole transporting materials on the power conversion efficiencies of devices were compared, followed by a discussion of the recent progress in hole-conductor-free solar cells. To date, the theoretical research on organohalide perovskites is neither fully comprehensive nor far-reaching. We then conducted a review of the progress of theoretical research on the atomic structure, band structure, and band gap of CH3NH3PbI3 and other analog perovskite materials. The advantages and disadvantages of popular theoretical methods and their issues, which would be helpful for developing computational work, are also discussed. Finally, we include a number of open questions relevant to this field and present some research topics for the future.