Ionic Influences on Recombination in Perovskite Solar Cells

The origins of recombination processes, particularly those that relate to IV hysteresis, are still unclear in perovskite solar cells. Of particular interest, is the impact different contact materials have on the level of hysteresis observed. This work shows that there is a clear link between ionic movement and interfacial recombination, which have both been shown to be responsible for hysteresis. By performing low temperature transient photovoltage (TPV) measurements over a period in which ions redistribute within the perovskite layer, the dominant recombination mechanism, responsible for hysteresis and other slow dynamic processes, is found to occur at the TiO2/perovskite interface. We observe an anomalous negative transient upon firing the laser pulse which we attribute to interfacial recombination at the TiO2/perovskite interface. The impact of recombination at the perovskite/HTL interface is shown to be negligible by performing TPV measurements using different laser wavelengths to probe different depths into the perovskite layer, as well as by changing the type of HTL used

Process optimization for producing hierarchical porous bamboo-derived carbon materials with ultrahigh specific surface area for lithium-sulfur batteries

Bamboo derived porous carbon materials, as inexpensive and environmentally friendly, microporous material sources, have been attracting enthusiastic attention for energy storage applications. In this work three different processes were employed to prepare three types of bamboo derived porous carbon materials. Among them, the sample prepared via a one-step activation method delivered the largest total pore volume (1.146 cm3 g−1) and the largest specific surface area (1824.4 m2 g−1) owning to a hierarchical porous structure. After the sample was used to encapsulate sulfur (S) to prepare carbon/S composite as cathodes for Li-S batteries. The composite loaded with 58.5 wt% S exhibited a high initial capacity of 1453 mAh g−1 at a rate of 0.1 C (1 C = 1675 mA g−1). A reversible capacity of 255 mAh g−1 was maintained after 500 cycles at 1 C with a capacity decay rate of only 0.0016% per cycle. This suggests that the bamboo derived porous carbon could be a promising conductive carbon matrix for carbon/S composite cathodes in Li–S batteries

In situ investigation of perovskite solar cells’ efficiency and stability in a mimic stratospheric environment for high-altitude pseudo-satellites

Perovskite solar cells with high power-per-weight have great potential to be used for aerospace applications such as satellites or high-altitude pseudo-satellites. The latter are unmanned aircraft exclusively powered by solar energy, typically flying in the stratosphere where the conditions of pressure, temperature and illumination are critically different from that on the earth's surface. In this work, we evaluate the performance and stability of high efficiency perovskite solar cells under a mimic stratospheric environment. In situ measurements under controlled conditions of pressure, temperature and illumination were developed. We show that the cells can operate efficiently in a large range of temperature from −50 °C to +20 °C, with a maximum power conversion efficiency at −20 °C, which is ideal for use in the stratosphere. Besides, performances are maintained after a number of temperature cycles down to −85 °C, representative of temperature variations due to diurnal cycles. An efficient encapsulation is developed, which could be critical to avoid the accelerated degradation of the cells under vacuum. Finally, a promising stability for 25 days of day–night cycles was demonstrated, which suggests that perovskite solar cells could be used to power high altitude pseudo-satellites

Enhanced Electrical Conductivity and Seebeck Coefficient in PEDOT:PSS via a Two-Step Ionic liquid and NaBH4 Treatment for Organic Thermoelectrics

A two-step approach of improving the thermoelectric properties of Poly(3,4-ethylenedioxythiophene)poly(4-styrenesulfonate) (PEDOT:PSS) via the addition of the ionic liquid, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM:TFSI) and subsequent reduction with NaBH4 is presented. The addition of 2.5 v/v% of EMIM:TFSI to PEDOT:PSS increases the electrical conductivity from 3 S·cm−1 to 1439 S·cm−1 at 40 °C. An additional post treatment using the reducing agent, NaBH4, increases the Seebeck coefficient of the film from 11 µV·K−1 to 30 µV·K−1 at 40 °C. The combined treatment gives an overall improvement in power factor increase from 0.04 µW·m−1·K−2 to 33 µW·m−1·K−2 below 140 °C. Raman and XPS measurements show that the increase in PEDOT:PSS conductivity is due to PSS separation from PEDOT and a conformational change of the PEDOT chains from the benzoid to quinoid molecular orientation. The improved Seebeck coefficient is due to a reduction of charge carriers which is evidenced from the UV–VIS depicting the emergence of polarons

Near Infrared Radiation as a Rapid Heating Technique for TiO2Films on Glass Mounted Dye-Sensitized Solar Cells

Near infrared radiation (NIR) has been used to enable the sintering of TiO2 films on fluorine-doped tin oxide (FTO) glass in 12.5 s. The 9 µm thick TiO2 films were constructed into working electrodes for dye-sensitized solar cells (DSCs) achieving similar photovoltaic performance to TiO2 films prepared by heating for 30 min in a convection oven. The ability of the FTO glass to heat upon 12.5 s exposure of NIR radiation was measured using an IR camera and demonstrated a peak temperature of 680°C; glass without the 600 nm FTO layer reached 350°C under identical conditions. In a typical DSC heating step, a TiO2 based paste is heated until the polymeric binder is removed leaving a mesoporous film. The weight loss associated with this step, as measured using thermogravimetric analysis, has been used to assess the efficacy of the FTO glass to heat sufficiently. Heat induced interparticle connectivity in the TiO2 film has also been assessed using optoelectronic transient measurements that can identify electron lifetime through the TiO2 film. An NIR treated device produced in 12.5 seconds shows comparable binder removal, electron lifetime, and efficiency to a device manufactured over 30 minutes in a conventional oven

Processing and Weathering of Sol-Gel Clearcoats for Coil-Coated Steel

Clearcoats provide long-term aesthetics and protection for underlying coating systems, increasing product lifetimes. However, organic clearcoats are predominantly produced using fossil-fuel feedstocks. In search of a sustainable alternative, an experimental investigation was conducted on the development of glass-like clearcoats produced using the sol-gel process. The processing of sol-gel clearcoats over a pigmented polyurethane coating was studied by modifying the sol-gel solution pH, aging, curing, precursor chemistry, and deposition techniques. Under optimal formulation and processing conditions, defect-free sol-gel clearcoats were produced that have potential to be scaled up to a coil-coating line using existing technologies. Mechanical testing demonstrated the coatings had excellent adhesion, hardness, and flexibility. Furthermore, accelerated laboratory weathering tests revealed the sol-gel coatings had superior degradation resistance compared to the organic coatings tested, resulting in negligible colour changes and higher gloss retention after 4000 hours of exposure. The durability and environmental benefits of sol-gel clearcoats highlight their potential as a replacement for traditional organic clearcoats in a variety of applications

Investigating spatial macroscopic metastability of perovskite solar cells with voltage dependent photoluminescence imaging

Metastability is a characteristic feature of perovskite solar cell (PSC) devices that affects powerrating measurements and general electrical behaviour. In this work the metastability of differenttypes of PSC devices is investigated through current–voltage (I–V) testing and voltage dependentphotoluminescence (PL-V) imaging. We show that advanced I–V parameter acquisition methodsneed to be applied for accurate PSC performance evaluation, and that misleading results can beobtained when using simple fast I–V curves, which can lead to incorrect estimation of cellefficiency. The method, as applied in this work, can also distinguish between metastability anddegradation, which is a crucial step towards reporting stabilised efficiencies of PSC devices. PL-V isthen used to investigate temporal and spatial PL response at different voltage steps. In addition tothe impact on current response, metastability effects are clearly observed in the spatial PL responseof different types of PSCs. The results imply that a high density of local defects andnon-uniformities leads to increased lateral metastability visible in PL-V measurements, which isdirectly linked to electrical metastability. This work indicates that existing quantitative PL imagingmethods and point-based PL measurements of PSC devices may need to be revisited, asassumptions such as the absence of lateral currents or uniform voltage bias across a cell area maynot be valid

Simultaneous Energy Harvesting and Hand Gesture Recognition in Large Area Monolithic Dye-Sensitized Solar Cells

Internet of Things (IoT) devices have become prevalent, embedding intelligence into our environment. It is projected that over 75 billion IoT devices will be connected by 2025 worldwide, with the majority being operated indoors. Dye-sensitized solar cells (DSSC) have recently been optimized for ambient light, having the capabilities of providing sufficient energy for self-powered IoT devices. Interaction with digital technologies, termed Human Computer Interaction (HCI), is often achieved via physical mechanisms (e.g. remote controls, cell phones) which can hinder the natural interface between users and IoT devices, a key consideration for HCI. What if the solar cell that is powering the IoT device can also recognize hand gestures which would allow the user to naturally interact with the system? Previous attempts to achieve this have necessarily employed an array of solar cell/photodiodes to detect directionality. In this work, we demonstrate that by monitoring the photocurrent output of an asymmetrically patterned monolithic (i.e., single cell) DSSC, and using machine learning, we can recognize simple hand gestures, achieving an accuracy prediction of 97.71%. This work shows that, DSSCs are the perfect choice for self-powered interactive technologies, both in terms of powering IoT devices in ambient light conditions and having aesthetic qualities that are prioritized by users. As well as powering interactive technologies, they can also provide a means of interactive control.Comment: Main body: 10 pages, 6 figures, 3 tables. Document includes supplementary info: 30 pages, 47 supplementary figure

Sources of Pb(0) artefacts during XPS analysis of lead halide perovskites

X-Ray Photoelectron spectroscopy (XPS) spectra of methyl ammonium lead halide perovskite films typically show the presence of lead as Pb(II), but Pb(0) is also often observed, potentially influencing the interpretation of the device physics. In this article the reproducible evolution of Pb(0) peaks which are likely artefacts generated under typical XPS analytical conditions are demonstrated from methyl ammonium lead halide films that contain no Pb(0) initially. The evolution of Pb(0) occurs via (1) X-ray photolysis under typical analytical conditions and (2) alongside other chemical changes as a result of film aging in air. In both cases we note the presence of PbI2 as a common factor contributing to in situ reactions to generate Pb(0) artefacts. Hence the observation of Pb(0) should be treated with extreme caution and here we recommend simple precautions to ensure materials analysis of these films gives reliable information when analyzed under UHV conditions

Investigating the Photostability of Organic Photovoltaics for Indoor and Outdoor Applications

Organic photovoltaics (OPVs) show great promise for both outdoor and indoor applications. However, there remains a lack of understanding around the stability of OPVs, particularly for indoor applications. In this work, the photostability of the poly[(thiophene)-alt-(6,7-difluoro-2-(2-hexyldecyloxy)quinoxaline)]:2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile blend is investigated for both outdoor and indoor applications. Photostability is found to vary drastically with illumination intensity. Devices under high-intensity white light-emitting diode (LED) illumination, with their short-circuit current density (JSC) matching JSC–EQE for AM1.5 G illumination, lose 42% of their initial performance after 30 days of illumination. Contrastingly, after almost 47 days of illumination devices under 1000 lux white LED illumination show no loss in performance. The poor photostability under 1 sun illumination is linked to the poor photostability of IDIC. Through Raman spectroscopy and mass spectrometry, IDIC is found to suffer from photoisomerization, which detrimentally impacts light absorption and carrier extraction. In this work, it is highlighted that under low light levels, the requirement of intrinsic material photostability may be less stringent