There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Long, balanced electron and hole diffusion lengths greater than 100 nanometers in the polycrystalline organolead trihalide compound CH3NH3PbI3 are critical for highly efficient perovskite solar cells. We found that the diffusion lengths in CH3NH3PbI3 single crystals grown by a solution-growth method can exceed 175 micrometers under 1 sun (100 mW cm(-2)) illumination and exceed 3 millimeters under weak light for both electrons and holes. The internal quantum efficiencies approach 100% in 3-millimeter-thick single-crystal perovskite solar cells under weak light. These long diffusion lengths result from greater carrier mobility, longer lifetime, and much smaller trap densities in the single crystals than in polycrystalline thin films. The long carrier diffusion lengths enabled the use of CH3NH3PbI3 in radiation sensing and energy harvesting through the gammavoltaic effect, with an efficiency of 3.9% measured with an intense cesium-137 source.

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Electron-hole diffusion lengths > 175 μm in solution-grown CH3NH3PbI3 single crystals

All of the cations currently used in perovskite solar cells abide by the tolerance factor for incorporation into the lattice. We show that the small and oxidation-stable rubidium cation (Rb + ) can be embedded into a “cation cascade” to create perovskite materials with excellent material properties. We achieved stabilized efficiencies of up to 21.6% (average value, 20.2%) on small areas (and a stabilized 19.0% on a cell 0.5 square centimeters in area) as well as an electroluminescence of 3.8%. The open-circuit voltage of 1.24 volts at a band gap of 1.63 electron volts leads to a loss in potential of 0.39 volts, versus 0.4 volts for commercial silicon cells. Polymer-coated cells maintained 95% of their initial performance at 85°C for 500 hours under full illumination and maximum power point tracking.

https://science.sciencemag.org/content/sci/early/2016/09/28/science.aah5557.full.pdf

Incorporation of rubidium cations into perovskite solar cells improves photovoltaic performance

State-of-the-art photovoltaics use high-purity, large-area, wafer-scale single-crystalline semiconductors grown by sophisticated, high-temperature crystal growth processes. We demonstrate a solution-based hot-casting technique to grow continuous, pinhole-free thin films of organometallic perovskites with millimeter-scale crystalline grains. We fabricated planar solar cells with efficiencies approaching 18%, with little cell-to-cell variability. The devices show hysteresis-free photovoltaic response, which had been a fundamental bottleneck for the stable operation of perovskite devices. Characterization and modeling attribute the improved performance to reduced bulk defects and improved charge carrier mobility in large-grain devices. We anticipate that this technique will lead the field toward synthesis of wafer-scale crystalline perovskites, necessary for the fabrication of high-efficiency solar cells, and will be applicable to several other material systems plagued by polydispersity, defects, and grain boundary recombination in solution-processed thin films.

/pdf/high-efficiency-solution-processed-perovskite-solar-cells-jmd7w75mq9.pdf

High-efficiency solution-processed perovskite solar cells with millimeter-scale grains

Three-dimensional organic-inorganic perovskites have emerged as one of the most promising thin-film solar cell materials owing to their remarkable photophysical properties, which have led to power conversion efficiencies exceeding 20 per cent, with the prospect of further improvements towards the Shockley-Queisser limit for a single‐junction solar cell (33.5 per cent). Besides efficiency, another critical factor for photovoltaics and other optoelectronic applications is environmental stability and photostability under operating conditions. In contrast to their three-dimensional counterparts, Ruddlesden-Popper phases--layered two-dimensional perovskite films--have shown promising stability, but poor efficiency at only 4.73 per cent. This relatively poor efficiency is attributed to the inhibition of out-of-plane charge transport by the organic cations, which act like insulating spacing layers between the conducting inorganic slabs. Here we overcome this issue in layered perovskites by producing thin films of near-single-crystalline quality, in which the crystallographic planes of the inorganic perovskite component have a strongly preferential out-of-plane alignment with respect to the contacts in planar solar cells to facilitate efficient charge transport. We report a photovoltaic efficiency of 12.52 per cent with no hysteresis, and the devices exhibit greatly improved stability in comparison to their three-dimensional counterparts when subjected to light, humidity and heat stress tests. Unencapsulated two-dimensional perovskite devices retain over 60 per cent of their efficiency for over 2,250 hours under constant, standard (AM1.5G) illumination, and exhibit greater tolerance to 65 per cent relative humidity than do three-dimensional equivalents. When the devices are encapsulated, the layered devices do not show any degradation under constant AM1.5G illumination or humidity. We anticipate that these results will lead to the growth of single-crystalline, solution-processed, layered, hybrid, perovskite thin films, which are essential for high-performance opto-electronic devices with technologically relevant long-term stability.

High-efficiency two-dimensional Ruddlesden–Popper perovskite solar cells

Visible-to-telecom converter, which converts the information from visible light to infrared telecommunication band, has huge potential in applications such as remote monitoring of visible light communication (VLC) links or sunlight illuminance in uninhabited regions to data centers. However, the existing converters based on parametric process suffer from high energy consumption, and a requirement of extra pumping supply. Herein we propose a passive visible-to-telecom converter by combining a perovskite solar cell with a silicon photonic chip, and further demonstrate its typical application scenario in monitoring VLC links. We succeed in converting the VLC signal with 200 kHz modulated rate into infrared light and transmitting it over 5-km-fiber without distortion. Thanks to the tunable bandgap properties of perovskite materials in perovskite solar cell, we double the capacity of a VLC link with a wavelength division multiplexing strategy. This visible-to-telecom converter via hybrid of perovskite and silicon photonics reveals potentials as a large range distributed visible-light sensor network converging on an optical interconnect data center.

Passive Visible-to-Telecom Converter Using Tunable Perovskites and Silicon Photonics

The invention discloses a novel solar cell The solar cell comprises a mesoscopic perovskite solar cell, thermoelectric cells and a radiator, which are stacked in sequence, wherein the mesoscopic perovskite solar cell and the thermoelectric cells are integrated by bonding or respectively depositing different P type and N type thermoelectric materials on a counter electrode of the mesoscopic perovskite solar cell through evaporation and deposition or growth technologies; and the mesoscopic perovskite solar cell is connected to the thermoelectric cells in series or in parallel The invention also discloses a preparation method of a stack device for the solar cell and the thermoelectric cell According to the solar cell and the preparation method thereof, through adoption of the brand-new structural design, the mesoscopic perovskite solar cell and the inorganic thermoelectric cells are stacked and integrated, and the corresponding preparation method is adopted to integrate, so that through the prepared solar cell, the influence on the service life of the device is avoided, the service life and the stability of the solar cell are improved, and more important, the utilization rate of the solar power is greatly improved

Composite solar cell and preparation method thereof

The invention discloses a process for using iodine lead formamidine as a light absorbing layer of a solar cell and an application thereof, wherein the light-absorbing layer of the solar cell is specifically perovskite containing iodine-lead formamidine component, and the preparation method comprises the following steps: (1) preparing a mesoporous structure; (2) preparing a precursor solution containing FAPbI3 iodolead formamidine perovskite: preparing raw materials including PbI2, FAI, CsI, etc. according to chemical dosage ratio, dissolving the raw materials in a solvent and then uniformly stirring to obtain a clear and transparent precursor solution; (3) putting the precursor into the mesoporous structure, standing, and then annealing in the solvent atmosphere to obtain the structure containing iodine lead formamidine. As a result of the anneal treatment assisted by the solvent vapor, the vapor assist of the solvent can slow down the crystallization while inhibiting the volatilization of iodoformamidine (FAI) and the like, so that the FAPbI3 can be stabilized in the black phase in the mesoporous film structure.

A process for using iodine lead formamidine as a light absorbing layer of a solar cell and an application thereof

In the rapid development of perovskite solar cells (PSCs), additive engineering has played a significant role for perovskite crystallization and passivation. The high density of defects at perovskite grain boundaries in the mesoporous scaffold leads to severe nonradiative recombination, which results in severe voltage loss. Herein, a sulfur‐containing Lewis base 2‐(methylthio)ethylamine hydrochloride (MTEACl) is applied in the perovskite precursor solution for printable mesoscopic PSCs with triple‐mesoscopic layer structure. Due to the strong electron donating ability of sulfur, the MTEACl can strongly interact with Pb2+, which can effectively passivate the defects of the perovskite. Correspondingly, the trap density of the perovskite is reduced, contributing to the improvement of power conversion efficiency from 15.18% to 17.17% and open circuit voltage to 995 mV.

Defect Passivation by a Sulfur‐Containing Lewis Base for Efficient Printable Mesoscopic Perovskite Solar Cells

Solar Cells: Crystallization Control of Ternary-Cation Perovskite Absorber in Triple-Mesoscopic Layer for Efficient Solar Cells (Adv. Energy Mater. 5/2020)

Anyi Mei

Papers

Passive Visible-to-Telecom Converter Using Tunable Perovskites and Silicon Photonics

Composite solar cell and preparation method thereof

A process for using iodine lead formamidine as a light absorbing layer of a solar cell and an application thereof

Defect Passivation by a Sulfur‐Containing Lewis Base for Efficient Printable Mesoscopic Perovskite Solar Cells

Solar Cells: Crystallization Control of Ternary-Cation Perovskite Absorber in Triple-Mesoscopic Layer for Efficient Solar Cells (Adv. Energy Mater. 5/2020)