Advancing perovskite solar cell technologies toward their theoretical power conversion efficiency (PCE) requires delicate control over the carrier dynamics throughout the entire device. By controlling the formation of the perovskite layer and careful choices of other materials, we suppressed carrier recombination in the absorber, facilitated carrier injection into the carrier transport layers, and maintained good carrier extraction at the electrodes. When measured via reverse bias scan, cell PCE is typically boosted to 16.6% on average, with the highest efficiency of ~19.3% in a planar geometry without antireflective coating. The fabrication of our perovskite solar cells was conducted in air and from solution at low temperatures, which should simplify manufacturing of large-area perovskite devices that are inexpensive and perform at high levels.

http://science.sciencemag.org/content/sci/345/6196/542.full.pdf

Interface engineering of highly efficient perovskite solar cells

Planar perovskite solar cells (PSCs) made entirely via solution processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, these PSCs require an electron-selective layer that performs well with similar processing. We report a contact-passivation strategy using chlorine-capped TiO2 colloidal nanocrystal film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after dark recovery) of their initial performance after 500 hours of continuous room-temperature operation at their maximum power point under 1-sun illumination (where 1 sun is defined as the standard illumination at AM1.5, or 1 kilowatt/square meter).

https://science.sciencemag.org/content/sci/early/2017/02/01/science.aai9081.full.pdf

Efficient and stable solution-processed planar perovskite solar cells via contact passivation.

Perovskite solar cells (PSCs) require both high efficiency and good long-term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole-transporting materials to achieve better performance. Here, we synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady-state efficiency of 22.85% for small-area (~0.094 cm2) cells and 21.7% efficiency (under reverse scanning) for large-area (~1 cm2) cells. We also achieve certified efficiencies of 22.6% (small-area cells, ~0.094 cm2) and 20.9% (large-area, ~1 cm2). The resultant device shows better thermal stability than the device with spiro-OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 °C. Interfacial losses between device layers play a key role in determining characteristics of solar cells. Jeon et al. address this in perovskite solar cells by synthesizing a hole-transporting layer that is better matched to the surrounding layers, and show high-efficiency and high-stability devices.

A fluorene-terminated hole-transporting material for highly efficient and stable perovskite solar cells

The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Metal halide perovskites of the general formula ABX3—where A is a monovalent cation such as caesium, methylammonium or formamidinium; B is divalent lead, tin or germanium; and X is a halide anion—have shown great potential as light harvesters for thin-film photovoltaics1–5. Among a large number of compositions investigated, the cubic α-phase of formamidinium lead triiodide (FAPbI3) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells6–9, and maximizing the performance of this material in such devices is of vital importance for the perovskite research community. Here we introduce an anion engineering concept that uses the pseudo-halide anion formate (HCOO−) to suppress anion-vacancy defects that are present at grain boundaries and at the surface of the perovskite films and to augment the crystallinity of the films. The resulting solar cell devices attain a power conversion efficiency of 25.6 per cent (certified 25.2 per cent), have long-term operational stability (450 hours) and show intense electroluminescence with external quantum efficiencies of more than 10 per cent. Our findings provide a direct route to eliminate the most abundant and deleterious lattice defects present in metal halide perovskites, providing a facile access to solution-processable films with improved optoelectronic performance. Incorporation of the pseudo-halide anion formate during the fabrication of α-FAPbI3 perovskite films eliminates deleterious iodide vacancies, yielding solar cell devices with a certified power conversion efficiency of 25.21 per cent and long-term operational stability.

/pdf/pseudo-halide-anion-engineering-for-a-fapbi3-perovskite-4k3k8u9skp.pdf

Pseudo-halide anion engineering for α-FAPbI3 perovskite solar cells.

1D Hexagonal HC(NH2)2PbI3 for Multilevel Resistive Switching Nonvolatile Memory

/pdf/negligible-pb-waste-and-upscalable-perovskite-deposition-3mwrvghykx.pdf

Negligible‐Pb‐Waste and Upscalable Perovskite Deposition Technology for High‐Operational‐Stability Perovskite Solar Modules

Scalable Fabrication of >90 cm 2 Perovskite Solar Modules with >1000 h Operational Stability Based on the Intermediate Phase Strategy

Various noble metal-free electrocatalysts have been explored to enhance the overall water splitting efficiency. Ni-based compounds have attracted substantial attention for achieving efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts. Here, we show superior electrocatalysts based on NiFe alloy electroformed by a roll-to-roll process. NiFe (oxy)hydroxide synthesized by an anodization method for the OER catalyst shows an overpotential of 250 mV at 10 mA cm-2, which is dramatically smaller than that of bare NiFe alloy with an overpotential of 380 mV at 10 mA cm-2. Electrodeposited NiMo films for the HER catalyst also exhibit a small overpotential of 100 mV at 10 mA cm-2 compared with that of bare NiFe alloy (550 mV at 10 mA cm-2). A combined spectroscopic and electrochemical analysis reveals a clear relationship between the surface chemistry of NiFe (oxy)hydroxide and the water splitting properties. These outstanding fully solution-processed catalysts facilitate superb overall water splitting properties due to enlarged active surfaces and highly active catalytic properties. We combined a solution-processed monolithic perovskite/Si tandem solar cell with MAPb(I0.85Br0.15)3 for the direct conversion of solar energy into hydrogen energy, leading to the high solar-to-hydrogen efficiency of 17.52%. Based on the cost-effective solution processes, our photovoltaic-electrocatalysis (PV-EC) system has advantages over latest high-performance solar water splitting systems.

Water Splitting Exceeding 17% Solar-to-Hydrogen Conversion Efficiency Using Solution-Processed Ni-Based Electrocatalysts and Perovskite/Si Tandem Solar Cell.

Silicon (Si) has attracted tremendous attention as a high-capacity anode material for next generation Li-ion batteries (LIBs); unfortunately, it suffers from poor cyclic stability due to excessive volume expansion and reduced electrical conductivity after repeated cycles. To circumvent these issues, we propose that Si can be complexed with electrically conductive Ti2O3 to significantly enhance the reversible capacity and cyclic stability of Si-based anodes. We prepared a ternary nanocomposite of Si/Ti2O3/reduced graphene oxide (rGO) using mechanical blending and subsequent thermal reduction of the Si, TiO2 nanoparticles, and rGO nanosheets. As a result, the obtained ternary nanocomposite exhibited a specific capacity of 985 mAh/g and a Coulombic efficiency of 98.4% after 100 cycles at a current density of 100 mA/g. Furthermore, these ternary nanocomposite anodes exhibited outstanding rate capability characteristics, even with an increased current density of 10 A/g. This excellent electrochemical performan...

Dae-Yong Son

Papers

1D Hexagonal HC(NH2)2PbI3 for Multilevel Resistive Switching Nonvolatile Memory

Negligible‐Pb‐Waste and Upscalable Perovskite Deposition Technology for High‐Operational‐Stability Perovskite Solar Modules

Scalable Fabrication of >90 cm 2 Perovskite Solar Modules with >1000 h Operational Stability Based on the Intermediate Phase Strategy

Water Splitting Exceeding 17% Solar-to-Hydrogen Conversion Efficiency Using Solution-Processed Ni-Based Electrocatalysts and Perovskite/Si Tandem Solar Cell.

Si/Ti2O3/Reduced Graphene Oxide Nanocomposite Anodes for Lithium-Ion Batteries with Highly Enhanced Cyclic Stability.