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.

Despite the impressive photovoltaic performances with power conversion efficiency beyond 22%, perovskite solar cells are poorly stable under operation, failing by far the market requirements. Various technological approaches have been proposed to overcome the instability problem, which, while delivering appreciable incremental improvements, are still far from a market-proof solution. Here we show one-year stable perovskite devices by engineering an ultra-stable 2D/3D (HOOC(CH2)4NH3)2PbI4/CH3NH3PbI3 perovskite junction. The 2D/3D forms an exceptional gradually-organized multi-dimensional interface that yields up to 12.9% efficiency in a carbon-based architecture, and 14.6% in standard mesoporous solar cells. To demonstrate the up-scale potential of our technology, we fabricate 10 × 10 cm2 solar modules by a fully printable industrial-scale process, delivering 11.2% efficiency stable for >10,000 h with zero loss in performances measured under controlled standard conditions. This innovative stable and low-cost architecture will enable the timely commercialization of perovskite solar cells. Up-scaling represents a key challenge for photovoltaics based on metal halide perovskites. Using a composite of 2D and 3D perovskites in combination with a printable carbon black/graphite counter electrode; Granciniet al., report 11.2% efficient modules stable over 10,000 hours.

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One-Year stable perovskite solar cells by 2D/3D interface engineering

Solar cells employing a halide perovskite with an organic cation now show power conversion efficiency of up to 22%. However, these cells are facing issues towards commercialization, such as the need to achieve long-term stability and the development of a manufacturing method for the reproducible fabrication of high-performance devices. Here, we propose a strategy to obtain stable and commercially viable perovskite solar cells. A reproducible manufacturing method is suggested, as well as routes to manage grain boundaries and interfacial charge transport. Electroluminescence is regarded as a metric to gauge theoretical efficiency. We highlight how optimizing the design of device architectures is important not only for achieving high efficiency but also for hysteresis-free and stable performance. We argue that reliable device characterization is needed to ensure the advance of this technology towards practical applications. We believe that perovskite-based devices can be competitive with silicon solar modules, and discuss issues related to the safe management of toxic material. Perovskite solar cells have emerged as a potential low-cost alternative to existing technologies. In this Perspective, Park et al. explore a strategy for the commercialisation of perovskite solar cells.

Towards stable and commercially available perovskite solar cells

Perovskite solar cells (PSCs) have now achieved efficiencies in excess of 22%, but very little is known about their long-term stability under thermal stress. So far, stability reports have hinted at the importance of substituting the organic components, but little attention has been given to the metal contact. We investigated the stability of state-of-the-art PSCs with efficiencies exceeding 20%. Remarkably, we found that exposing PSCs to a temperature of 70 °C is enough to induce gold migration through the hole-transporting layer (HTL), spiro-MeOTAD, and into the perovskite material, which in turn severely affects the device performance metrics under working conditions. Importantly, we found that the main cause of irreversible degradation is not due to decomposition of the organic and hybrid perovskite layers. By introducing a Cr metal interlayer between the HTL and gold electrode, high-temperature-induced irreversible long-term losses are avoided. This key finding is essential in the quest for achieving...

Not All That Glitters Is Gold: Metal-Migration-Induced Degradation in Perovskite Solar Cells.

Methylammonium lead halide perovskites are attracting intense interest as promising materials for next-generation solar cells, but serious issues related to long-term stability need to be addressed. Perovskite films based on CH3NH3PbI3 undergo rapid degradation when exposed to oxygen and light. Here, we report mechanistic insights into this oxygen-induced photodegradation from a range of experimental and computational techniques. We find fast oxygen diffusion into CH3NH3PbI3 films is accompanied by photo-induced formation of highly reactive superoxide species. Perovskite films composed of small crystallites show higher yields of superoxide and lower stability. Ab initio simulations indicate that iodide vacancies are the preferred sites in mediating the photo-induced formation of superoxide species from oxygen. Thin-film passivation with iodide salts is shown to enhance film and device stability. The understanding of degradation phenomena gained from this study is important for the future design and optimization of stable perovskite solar cells.

/pdf/fast-oxygen-diffusion-and-iodide-defects-mediate-oxygen-56wdtamn4o.pdf

Fast oxygen diffusion and iodide defects mediate oxygen-induced degradation of perovskite solar cells.

Organometal halide perovskite solar cells have evolved in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) reached 20.1% late last year. The key disquiet was stability, which has been limiting practical application, but now the state of the art is promising, being measured in thousands of hours. These improvements have been achieved through the application of different materials, interfaces and device architecture optimizations, especially after the investigation of hole conductor free mesoporous devices incorporating carbon electrodes, which promise stable, low cost and easy device fabrication methods. However, this work is still far from complete. There are various issues associated with the degradation of Omh-perovskite, and the interface and device instability which must be addressed to achieve good reproducibility and long lifetimes for Omh-PSCs with high conversion efficiencies. A comprehensive understanding of these issues is required to achieve breakthroughs in stability and practical outdoor applications of Omh-PSCs. For successful small and large scale applications, besides the improvement of the PCE, the stability of Omh-PSCs has to be improved. The causes of failure and associated mechanisms of device degradation, followed by the origins of degradation, approaches to improve stability, and methods and protocols are discussed in detail and form the main focus of this review article.

Organometal halide perovskite solar cells: degradation and stability

Hydrogen-doped zinc oxide (ZnO:H) films were deposited by rf magnetron sputtering as transparent conductive films. The resistivity of ZnO:H film was significantly reduced by the addition of H2 in Ar during rf sputtering. The electrical resistivity of ZnO:H films reached 2×10−4Ωcm. The carrier concentration increased with increasing H2 concentration during deposition. X-ray diffraction results showed that the d0002 interplanar spacing increased with increasing H2 concentrations. The carrier concentration was significantly reduced in two orders of magnitude by increasing the substrate temperature from 150 to 250 °C during deposition. Both results suggested that the increase of carrier concentration by adding H2 during sputtering was due to the hydrogen donor rather than the oxygen vacancies in ZnO films, consistent with the theoretical predictions by Van de Walle. UV–visible spectroscopy further showed that the transmittance is high up to 100% in the visible range. The band gap determined by optical absorpt...

/pdf/hydrogen-doped-high-conductivity-zno-films-deposited-by-woi56gwgq9.pdf

Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering

Visible electroluminescence from silicon nanocrystals (Si-NCs) embedded in amorphous silicon nitride (a‐SiNx) films has been observed. The Si‐NC∕a‐SiNx films were deposited by evaporating silicon from electron gun into the inductively coupled plasma of nitrogen. The density of Si-NCs in the a‐SiNx matrix was around 1012cm−2. Strong room temperature photoluminescence was observed in 2.8 and 3.0eV, different from literature values. The electroluminescence (EL) devices were fabricated with Si‐NCs∕a‐SiNx film as the active layer using the Al or Ca∕Ag cathode and the indium tin oxide anode. Through tunneling, the electrons and holes were respectively injected from the cathode and anode into Si-NCs and confined within Si-NCs for light emission by the high band gap a‐SiNx matrix. For the device with Ca∕Ag cathode, the turn-on voltage was as low as 10V and the EL efficiency was about 1.6×10−1 Cd∕A. The EL spectra consisted of two broad peaks centered around 2.5 and 2.8eV. Our results demonstrate that Si‐NCs∕a‐SiN...

/pdf/visible-electroluminescence-from-silicon-nanocrystals-4jkiwg4mnv.pdf

Visible electroluminescence from silicon nanocrystals embedded in amorphous silicon nitride matrix

In this study, ZnO nanowire arrays were prepared using a hydrothermal method. During growth, polyethyleneimine (PEI) and ammonia were added to adjust the structure and optical properties of the ZnO nanowires. Emission analysis revealed visible photoluminescence emissions from ZnO nanowires produced under various growth conditions. To correlate the relationship between visible emissions and structural defects in ZnO nanowires, we employed X-ray absorption spectroscopy (XAS) to characterize the coordination number and bond length of the ZnO nanowires. On the basis of analytical results, we determined that the red emission is attributed to interstitial zinc defects (Zni) and the yellow emission is attributed to interstitial oxygen defects (Oi).

Influence of Polyethyleneimine and Ammonium on the Growth of ZnO Nanowires by Hydrothermal Method

Diamond-like carbon (DLC) nanocomposite films were deposited at room temperature by inductively coupled plasma chemical vapor deposition using hexamethyldisilane (HMDS), hexamethyldisilazane (HMDSN), and hexamethyldisiloxane (HMDSO) precursors. High-resolution transmission electron microscopy showed that all the films contained nanoparticles. The DLC nanocomposite films deposited by HMDS contained hollow spherical nanocrystallites, called nanoballs, of hexagonal silicon carbide. The nanocomposite films deposited by HMDSN contained crystalline Si3N4 nanoparticles. The nanocomposite films deposited by HMDSO contained amorphous SiOx nanoparticles. Although both types of films had similar hardness, the DLC nanocomposite films exhibited much lower compressive stresses than the DLC films deposited by methane, i.e., 1.5 vs 11 GPa, respectively. Through the enhancement of gas phase reactions, the inductively coupled plasma should be responsible for the formation of nanoparticles in the nanocomposite films.

http://ir.lib.ncku.edu.tw/bitstream/987654321/90700/2/3010301501025.pdf

Liang-Yih Chen

Papers

Organometal halide perovskite solar cells: degradation and stability

Hydrogen-doped high conductivity ZnO films deposited by radio-frequency magnetron sputtering

Visible electroluminescence from silicon nanocrystals embedded in amorphous silicon nitride matrix

Influence of Polyethyleneimine and Ammonium on the Growth of ZnO Nanowires by Hydrothermal Method

Diamond-like carbon nanocomposite films