Integrating storage technologies in the future renewable energy system is one of the most important nowadays problems. Recent developments in small scale consumer electronics, trend for implementing “Internet of Things” and smart house smart cities concepts make it imperative to have cheap, wireless power solution for all-time operation electronics. The combination of photovoltaic (PV) devices with rechargeable batteries represents a viable strategy for powering such low power electronic devices. With the increasing use of indoor LED (light emitting diode) lighting worldwide, the matching LED output spectrum with the absorption spectrum of lead halide perovskite solar cells (PSC) affords an opportunity to reuse emitted light with high efficiency to feed low power electronics. Recently, lead halide perovskite cells and modules have demonstrated efficiencies under artificial lighting in excess of 30 % [1] with a record of 40.1 % achieved with an extra thick absorber layer [2]. The main reason bringing forward PSCs is very close overlap of the external quantum efficiency in lead halide perovskite solar cells with the emission spectrum of an LED lamp. However, there is not many publications showing a combination of perovskite-battery devices working efficiently under low light LED illumination intensities.

AIM AND APPROACH

The aim of the work is to demonstrate a successful and highly efficient energy harvesting and storage under a wide range of light emitting diode (LED) illumination intensities by applying lead halide perovskite solar module directly coupled to a high-rate capable next generation sodium ion battery. Direct coupling of PV and batteries require fabrication of perovskite solar module with tailored current-voltage (IV) characteristic to match battery voltage under target irradiance conditions. A 3-cell perovskite module with CH3NH3Pb(I0.8Br0.2)3 absorber layer and fullerene electron transport layer [3] was fabricated with a conversion efficiency of 17.8 %, with a fill factor of 81.3 %, short-circuit current density of 5.91 mAcm-2 and open-circuit voltage of 3.71 V under AM.1.5 illumination. To test the PSC modules for indoor battery charging under LED lighting a sodium ion battery with metallic sodium anode and cathode made from sodium titanium phosphate (NaTi2(PO4)2) coated onto sheets of carbon Nano felt (NTP@CNF) was chosen due to its high charge rate capability, low charge-discharge overpotential and distinct charge and discharge voltage plateau [4]. LED illumination intensity was attenuated by using neutral density filters.

CONCLUSION

High efficiency indoor charging of advanced sodium ion battery based on sodium titanium phosphate (NaTi2(PO4)2) coated onto sheets of carbon Nano felt using a perovskite solar module with CH3NH3Pb(I0.8Br0.2)3 absorber layer under LED illumination was demonstrated. We have directly coupled both devices without any power electronics and achieved overall PV-Battery efficiency of 24.3% under LED illumination. Under target LED illuminance of 300 lux, the perovskite solar cell shows PCE of 29.4%, and coupling factor of 0.87, and roundtrip battery efficiency of 94.9 % [5].

[5] Kin L.C-., Joule, ‘Efficient indoor light harvesting with MAP(I0.8Br0.2)3 solar modules and Na-ion battery’ 2022 submitted.

Perovskite solar cells have emerged as a promising and highly efficient solar technology. Despite efficiencies continuing to climb, reaching a new record of 25.7%¹, the prospect of industrial manufacture is in part hampered by concerns regarding the safety and sustainability of the solvents used in lab scale manufacture. Here, we aim to present a methodology for green solvent selection informed by EHS considerations from the CHEM-21 solvent guide for succesful methylammonium lead triiodide (MAPbI₃) precursor dissolution². Through the use of this methodology we present a N,N-dimethylformamide (DMF)-free alternative solvent system for deposition of MAPbI₃ precursors (MAI and PbI₂) consisting of dimethyl sulfoxide (DMSO), dimethylpropyleneurea (DMPU), 2-methyltetrahydrofuran (2-MeTHF) and ethanol (EtOH). Perovskite films cast from the three candidate solutions show improved crystallinity, higher fluorescence emission, and improved crystal size uniformity than those cast from DMF/DMSO and similar photovoltaic performance (16.2% for DMF/DMSO, 16.1% for candidate A solvent system²). We will cover the key solvent parameters which determine effective MAPbI₃ precursor dissolution; provide a set of criteria for appropriate alternative solvent selection; and demonstrate the application of green chemistry principles to solvent selection for perovskite photovoltaic manufacturing. Due to significant advancement in the perovskite research sphere, more thermally stable and efficient perovskite compositions have risen to prominence. This includes the now ubiquitous  ‘triple cation’ perovskite (Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃)³, providing increased impetus to study solvent interactions in these more complex colloidal dispersions. We will discuss recent progress towards  ‘green’ solvent engineering strategies specifically tailored towards these compositions, further highlighting key parameters requiring control to potentially improve the optoelectronic properties of this promising material.

1            Best Research-Cell Efficiency Chart | Photovoltaic Research | NREL, https://www.nrel.gov/pv/cell-efficiency.html, (accessed 7 April 2020).

2            A. J. Doolin, R. G. Charles, C. S. P. De Castro, R. G. Rodriguez, E. V. Péan, R. Patidar, T. Dunlop, C. Charbonneau, T. Watson and M. L. Davies, Green Chem., 2021, 23, 2471–2486.

3            M. Saliba, J.-P. Correa-Baena, C. M. Wolff, M. Stolterfoht, N. Phung, S. Albrecht, D. Neher and A. Abate, Chem. Mater., 2018, 30, 4193–4201.

Thermal processing is critical in preparing the functional layers for perovskite solar cells (PSCs), such as metal oxides (TiO₂ and SnO₂) electron transport layers (ETLs), and perovskite layer. The conventional thermal processing method using a furnace or hotplate with a time-consuming heating and cooling period impedes the possibility of achieving a rapid and in-line production for the commercialization of PSCs.

Laser processing is an advanced manufacturing method that owns various advantages over conventional thermal processing, including being rapid, scalable, contact-free, area-selective, and causing minimal thermal damage.

In this presentation, I will summarize our recent studies carried out at The University of Manchester using lasers to fabricate a range of ETLs, including compact and mesoporous TiO₂, Ta-doped TiO₂, SnO₂, and ZnO for efficient rigid and flexible PSCs [1-3]. In addition, I will introduce our latest study using the laser-induced graphene decorated with the NiO_x nanoparticles as the back electrode for hole-transport-layer-free PSCs.

The intensive research on perovskite solar cells (PSC) in the last years has allowed the technology to reach exceptional results, with a record power conversion efficiency (PCE) of 25.5% [1] for single junction cells. Due to low temperature processing, band gap tunability and flexible composition, this class of materials is also highly employed in multijunction, or tandem, photovoltaic applications. With so many demonstrated advantages, one of the remaining challenges for the industrialization and commercialization of the technology is the upscaling of fabrication of perovskite films. Large-area deposition methods such as (ultrasonic) spray coating, inkjet printing, slot dye coating, and blade coating provide great avenues for high throughput fabrication, but often come with a significant decrease in PCE when compared to spin coated devices [2].

This study proposes a design of experiment approach, aiming to optimize the fabrication of perovskite thin films by ultrasonic spray coating. Initially the entire process was reviewed, from substrate cleaning and solution preparation to deposition and post treatment of the film, and key parameters were drawn out. Based on this analysis, and previous studies [3], experiments were designed to gain further insight on two important steps of the process: the deposition of a wet layer of precursor solution by ultrasonic spray coating, and the gas-quenching of the solvent for perovskite crystallization.

The deposition step was examined by a one factor at a time (OFAT) approach, with the establishment of a set of standard parameters and the variation and analysis of each parameter individually. By doing so it was possible to verify that the spray coating parameter are paramount to the formation of a homogeneous wet layer and good coverage of the substrate, yet the fine tuning of the perovskite crystallization, and consequentially the layer quality, depends mostly on the evaporation step.

The gas quenching-assisted evaporation was then thoroughly studied by a full factorial analysis of three key parameters: gas (nitrogen) pressure, distance between nitrogen gun and substrate, and solvent volatility, determined by the ratio between a low volatile and a high volatile solvent. The produced films were then characterized in regard to their morphology and performance as the active layer of a solar cell.

This full factorial analysis provided insight on the complex mechanism of perovskite crystallization in a thin film. It also allowed the assessment of interactions between the parameters and shed light on how they influence the evaporation of solvent in different regimes. Moreover, the use of design of experiments resulted in higher efficiencies than the previously trial-and-error approach, with the best performing cell reaching a PCE of 18.1%, which is in line with spin coated perovskite solar cells with similar architecture, i.e. nickel oxide (NiOx) as hole transport layer, no additives on the perovskite solution, and no anti-reflection or passivation layers.

Perovskite-based solar cells have shaken the photovoltaic sector achieving more than 25% efficient laboratory-scale solar cells in around 10 years. Now, they are on the way to breaking the 30% efficiency threshold by being coupled with established technologies such as Silicon and CI(G)S forming a multijunction configuration.

As demand for a more sustainable and decentralized electricity system increases, low-cost and lightweight thin-film based multijunction are an ideal match for integrated PV requirements. On the other hand, urban environments increase stress-induced losses due to partial shading and weather alterations on PV strings. Most importantly, both thin-film technologies (CIGS and Perovskite) have shown lower reverse breakdown voltages[1-2], which increases the need for bypass diodes and in some cases reverse bias-induced degradation [3]. It is therefore essential to consider alternative module designs to optimize the desired power outputs and increase the long term reliability of BIPV/VIPV systems.

In this study, we designed an improved SPICE simulation[4] of a PV module to assess the impact of material’s and design’s parameters under partial shadow conditions, with a focus on alternative designs for thin-film based integrated photovoltaics applications. To guarantee safe real life installation and operation, realistic limitations are also taken into consideration as boundary conditions. As a result of our research, we present suitable alternative designs based on different absorber materials, sizes, and interconnection schemes and inclusive of 2 terminal, current matched multijunction CIGS/Perovskite devices. For each configuration, we also report the local impact of shadow-induced thermal losses based on a SPICE equivalent thermal circuit.

A solar cell is an energy conversion device from natural to renewable energy. Since the supplying energy from a solar cell fluctuates, energy storage is required for a user-on-demand energy supply system. The energy needs to change into the storable form of a battery and of hydrogen. The battery can respond to rapid power change, but the cost is proportional to the storage size. Therefore, it is suitable for a relatively small amount of energy storage. Hydrogen is good for relatively large energy storage because the storage cost is not so expensive. However, it is not suitable for a rapid reaction because the water electrolyzer and fuel cell respond slowly. Thus, the hybrid system of the battery and hydrogen storage is needed for the user-on-demand and especially for the independent energy supply system. The system optimization is, however, still obscure due to its complexity. Suitable device characteristics are also needed for system optimization.

The first discussion point is the device size and efficiency of the system. The direct use of the generated energy from the solar cells is the most efficient, but the user needs the energy independent of the solar power generation period. Thus, the capacity of the storage and the conversion efficiency of devices must be considered in the design of the energy supply system. The design is complicated especially for the battery and hydrogen hybrid storage system due to the multiple storage devices existing in a system. The system design procedure was evaluated using the independent self-controlled energy supply system [1]. It was clarified that the energy storage methods and the generated power by solar cells or the user demand are essential to determine the system size.

The second discussion point is that the device response affects the system's operation. The DC/DC converter is used in the system to convert the voltage between the DC bus line and the device operations [1]. A typical DC/DC converter focuses on the current stability and not on the instantaneous over- or under-voltage existing at the step-like current change. Especially, small-sized DC/DC converters tend to be observed these voltages. These instantaneous voltages affect the system operation and make the system operation unstable in some cases. The response without these voltages was found to be important for stable system operation.

Solution-processed organic, and perovskite solar cells have reached promising power conversion efficiency (PCE) records in recent years on cells with active area <1 cm². Transferring the performance from laboratory scale to real modules is typically associated with losses in PCE. The origin of such upscaling losses is manifold and includes potential drops in the electrodes due to a non-optimized electrode design or an increase of defects and inhomogeneities of the active layers. To minimize those losses, the first step is to quantify the significance of each loss channel. In the first part, we use a combination of straightforward steady-state measurement techniques on lab-scale devices and mini-modules with a photoactive area of ~37 cm² to set up a reliable digital twin of the device in the FEM-based simulation tool Laoss. This digital twin allows us to understand the existing performance limitation of the fabricated device. In a second step, the model is used to optimize performance by sequentially switching off various losses, varying the geometry of the module and combining this to obtain a thorough loss diagram. For the specific module, it is found that 50% of the PCE is lost due to an internal series resistance when moving from lab to module scale. It is attributed to a modified interface when partially fabricated in ambient conditions. This could be further evidenced by evaluating the performance of small cells as well as by electro- (EL) and photoluminescence imaging. In the second part, we use imaging techniques (EL and dark lock-in thermography) to detect different impurities and defects in perovskite solar cells. We find features that can be related to manufacturing issues but also point-like defects that occur during storage. With simulations, we can quantify the latter and eventually follow its evolution during storage time.

Organic semiconductor-based photovoltaic (OPV) devices have many properties that make them attractive for indoor applications, such as tailorable light absorption, low embodied energy manufacturing and cost, structural conformality, and low material toxicity. Compared to their use as organic solar cells for standard outdoor solar harvesting, indoor OPV (IOPV) devices operate at low light intensities and thus demonstrate different area-scaling behaviour. In particular, the performance of large-area IOPV devices is much less affected by the sheet resistances of the transparent conductive electrodes (a major limit in organic solar cells), but instead by factors such as their shunt resistance at low light intensities. Herein, we review physical insight into IOPV systems using drift-diffusion and finite element modelling and compare this to real devices measured under indoor lighting conditions. Measurement considerations for IOPV devices are reviewed to accurately compare figures of merit necessary for the systems integration into the internet of things (IoT) and embedded sensor applications.

A unique property of metal halide perovskite solar cells materials is their widely tunable optical bandgap, which enables their use in multijunction solar cells. However, both mixed-halide wide-bandgap perovskites and lead-tin narrow-bandgap perovskites suffer from non-radiative recombination due to the formation of bulk traps and interfacial recombination centers which limit the open-circuit voltage of sub-cells and consequently of the integrated tandem. Additionally, the complex optical stack in a multijunction solar cell can lead to losses stemming from parasitic absorption and reflection of incident light which aggravates the current mismatch between sub-cells, thereby limiting the short-circuit current density of the tandem. Here, we present an integrated all-perovskite tandem solar cell that uses surface passivation strategies to reduce non-radiative recombination at the perovskite-fullerene interfaces, yielding a high open-circuit voltage. By using optically benign transparent electrode and charge-transport layers, absorption in the narrow-bandgap sub-cell is improved, leading to an improvement in current-matching between sub-cells. Collectively, these strategies allow the development of a monolithic tandem solar cell exhibiting a power-conversion efficiency of over 23%.

Achieving deep impacts on greenhouse gas emissions and efficient energy use through use of renewable technologies such as photovoltaics will require the thoughtful integration of the solar module into a final application. The overall efficiency of solar energy utilisation can be improved if the module is integrated with another function, such as photochemical energy conversion, solar thermal conversion, plant growth or energy storage. Organic photovoltaic technology brings potential advantages to some applications where spectral sharing or flexible form factor are needed. In other cases, the choice of PV technology may be much less important than other components or overall system design. Optimising the integrated system requires understanding of the optical and electrical response of the solar module in different conditions, control of those properties and suitable models of the whole system performance.   We will present examples of the integration of PV with other functions, including photochemical energy conversion, and consider how system design and operation influence overall performance.  

OPV efficiency values are moving towards > 20 % for small area cells and > 15 % for large scale modules. With these performance values, OPV is reaching out to applications that are going beyond the typical niche markets. Integration of OPV into functional objects is attractive for building integrated / attached PV, window integrated PV, vehicle integrated PV, textile PV or agri-/horti PV. Most interestingly, all these application scenarios are related to flexibility and light weight. However, besides few demonstrations of ultra-flexible and foldable organic solar cells, the limitations of lightweight OPV that is compatible to mass production are not fully understood.

OPV devices require encapsulation by barrier films to reduce the degradation driven by extrinsic factors, which in turn limits their flexibility and leads to lower specific power values. In this talk, we analyze the packaging requirements for light weight cells and modules. Fully solution-processed and semitransparent organic solar cells performing comparable with conventional indium tin oxide-based devices are processed directly onto different barrier films of varying thicknesses. Direct cell fabrication onto barrier films leads to the elimination of the additional PET substrate and one of the two adhesive layers. In addition to the increase of the specific power to 0.38 W/g, which is more than four times higher than sandwich-encapsulated devices. These organic solar cells exhibit better flexibility and survive 5000 bending cycles with 4.5 mm bending radius, show comparable stability as conventionally encapsulated devices under constant illumination (1 sun) in ambient air for 1000 h. A further step to increase the W/g Figure of Merit is to replace the top laminated barrier by a printed barrier, reducing the weight by another factor of 2. In combination with high performance NFA based composites, these architectures have the potential to overcome the 1 W/gr milestone while still being compatible to roll to roll production.

Intel corporation predict that by the end of 2020, up to 200 billion connected Internet of Things (IoT) devices came online and this is predicted to consume over 1000 TWh yr-1 by 2025. To put this in perspective, this is over 1300 x the energy output of EU’s largest solar plant, Núñez de Balboa. The increasing digital interconnectivity of our everyday lives means that this energy burden will only increase in the coming decades. In addition, many portable IoT devices incorporate primary batteries, which consume valuable materials. One solution to this growing demand is the coupling of IoT nodes with energy harvesting devices, such as photovoltaics cells which could provide power to IoT nodes and avoid the need to replace primary batteries.

Hybrid solar cells such as perovskites, OPVs and DSSCs, have all shown promising performance in ambient light [1], meaning that any of these technologies could be candidates to power future IoT devices. Despite the promise of these PV technologies, work needs to be done especially around standards for testing. There is currently no consensus on what constitutes “ambient light” both in terms of spectral and power output and it is difficult to compare results from one laboratory to the next. We can predict the path of the Sun for any given point on Earth, but predicting how much light power is available in any given ambient scenario is difficult and reliant on human factors such as available light sources (e.g. CFT, LED, natural, or combination) and position of the solar cell relative to the light source.

This presentation will explore these issues, discussing what we mean when we say low or ambient light, and showing the results of maximum power measurement in real and simulated scenarios and how in some cases, an IV curve measured at single lux value is not an accurate predicator of real-world performance. Examples of IoT devices powered by organic and perovskite PVs will be shown and real-World performance discussed.

Semi-transparent Organic Solar Cells (ST-OSCs) have unparalleled ability to tailor the optical transmission to a targeted application such as their integration into buildings, where color-neutrality is generally favored, and integration into greenhouses, where the transmision might be matched to the light needs of plants. Plants have a complex response to light quality (the spectral distributions) and light quantity (the total intensity) and have often adopted to a particular envionment. For example, lattice is a low light plant that can get severely stressed above 20% of solar radiation, at which point photosynthesis plateaus and excess energy if converted into protective molecules such as anthocyanines or shunted. In contrast, tomatoes are high light intensity plants. We will discuss the status of work by a team at NCSU to energy balances, economics, and the impact of filtered light on plant growth. We find that the heating and colling requirements can be significantly effected by ST-OSCs and that greenhouses with net-zero energy balance can be operated in all but the coldest climates in the US [1]. Additionally, studies on lettucie indicate no negative impact on yield [2]. This energy balance in yield translates into favorouble economics when comparing ST-OSC greenhouses to conventional greenhouses across many different climate classes [3]. Interestingly, the use ST-OSC can also impact genetic expression and alter for example the plant’s nitrogen utilization [4]. All these factors bode well for this application of ST-OSC technology and the use-case is rather stong. Yet, the problems regarding lifetime of the devices and fabrication costs of properly encapsualted and integrated modules have yet to be solved.

Organic solar cells allow for unobtrusive integration into surfaces of consumer electronics that are hardly feasible with established technologies. Alongside with excellent low-light performance, both opaque and semi-transparent solar cells can fit arbitrary shapes and match various colors.^[1] To date, the main application for photovoltaics is power generation for the electric grid and accordingly the development of photovoltaics focuses on lowering production costs and maximizing power conversion efficiencies under direct sun illumination. Yet, emerging applications for autarkic IoT devices demand rethinking of what the optimization parameters for photovoltaics are.

Here we demonstrate fascinating properties of self-sufficient “Solar Glasses” – sunglasses that feature semi-transparent organic solar cells instead of shaded lenses.^[2]

Quite literally hidden in plain sight, the solar cells serve both as light sensors and live power supply for integrated electronics and LC displays simply by harvesting ambient light. This talk dives into the special requirements and novel opportunities for mobile sensor applications and indoor photovoltaics that are remarkably different from classical power harvesting solar cells.

Organic-inorganic hybrid perovskite photovoltaics have attracted tremendous attention due to rapid progress in terms of power conversion efficiency in the last few years, from 3.8% to present record values in excess of 25%. However, fundamental problems, such as the toxicity of hybrid lead halide perovskites, hysteresis and structural instability remain to be solved for their application and commercialization. Indeed, the low-temperature solution-processing of perovskite films inevitably causes formation of a certain amount of defects on the surface and at the grain boundaries, which lead to serious trapping, charge accumulation, and recombination problems as well as stability issue. We pursue the interface engineering, defects passivation, and dimensional tunability approaches via introducing various types of multifunctional conjugated organic compounds to improve the stability and performance of perovskite photovoltaics.  

In this presentation, we will discuss our achieved results in details for the above-mentioned approaches with a central focus on the fundamental complexity of microstructure and charge transport mechanisms and their correlation to the device performance, stability and indoor application.

In the recent years, Perovskite solar cells (PSCs) have achieved impressive efficiencies and have progressed on the scale of technological availability close to becoming a potential reality for the market. However, many challenges still need to be addressed to enable full industrial production and commercialization.
Basic research is continually developing and understanding the interactions of materials to increase efficiency and lifetime but most of the time do not taken in consideration the need in a large-scale production, such as solvent toxicity, materials degradetion, the establishment of the supply chain, costs and CAPital expenditure of the production line (CAPEX). Therefore, the technological scale-up, from small laboratory cells to real-size modules and panels, involves several steps and peculiarities. 
In the field of PSC, the best results currently obtained on small devices are found on chlorinated or halogen based inks processed in an inert atmosphere, which favor a better crystallization of the active layer and translate into higher performance. Furthermore, lead-based perovskites are the most ready option for a potential market in terms of performance and relative ease of manufacture. However, those formulations are not the best choice for scale-up due to health and safety concerns and best practices, requiring the development of safety control protocols that are not an issue in small-scale or laboratory research. 
In this work, we present the main challenges of increasing PSC from rigid laboratory-scale devices to flexible cells fabricated with scalable processing techniques. The transfer from doctor blade devices prepared under controlled conditions (RH <35%) to roll-to-roll solt-die (R2R) coated films manufactured in a laboratory setting (ISO-7 cleanroom) is reported, paving the way for future industrialization of this promising photovoltaic technology.