A Review of Integrated Systems Based on Perovskite Solar Cells and Energy Storage Units: Fundamental, Progresses, Challenges, and Perspectives

A Comprehensive Review on Perovskite Solar Cells Integrated Photo-supercapacitors and Perovskites-Based Electrochemical Supercapacitors

Perovskite solar cells (PSCs) have rapidly become a prevalent photovoltaic technology owing to their simple structure, low processing cost, and remarkable increase in solar-to-electric power conversion efficiency (PCE). However, the intermittent nature of solar radiation induces some technical and financial challenges for its practical applications as a reliable power source. To address this issue, the integration of PSCs with supercapacitors (SCs) in the form of integrated photo-supercapacitors (IPSs) has gathered significant attention. This integration can balance energy availability and demand, reduce energy wastage, and stabilize power output for portable and wearable electronics. Meanwhile, the excellent optoelectronic properties with mixed electronic and ionic conductivity of metal halide perovskites (MHPs) have expanded their application as electrode and electrolyte materials for SCs and photo-supercapacitors (PSs) applications. This review provides an all-inclusive summary of the current state-of-the-art research progress of PSCs-IPSs and MHPs-based SCs and PSs by highlighting their basics and integration approaches. It also discusses the challenges and prospects of these materials and technologies.

Dual-edged sword of ion migration in perovskite materials for simultaneous energy harvesting and storage application

Portable electronic devices and Internet of Things (IoT) require an uninterrupted power supply for their optimum performance and are key ingredients of the futuristic smart buildings - cities. The off-grid photovoltaic cells and photo-rechargeable energy storage devices meet the requirements for continuous data processing and transmission. In addition, these off-grid devices can solve the energy mismanagement problem famously called as "duck curve". The conventional approach is the external integration of a photovoltaic cell and an energy storage device through a complex multi-layered structure. However, this approach causes ohmic transport losses and requires additional complex device packaging leading to increased weight and high cost. Toward this narrative, in this viewpoint, we shed light on application of disruptive organic-inorganic hybrid halide perovskite bifunctional materials employed as smart photo-rechargeable energy devices. We also present hybrid halide lead-free perovskite materials for off-grid energy storage systems for indoor lighting applications.

Preparation of Nanostructured Sn/Ti Oxide Hybrid Films with Terpineol/PEG-Based Nanofluids: Perovskite Solar Cell Applications

Tin oxide (SnO₂) and titanium dioxide (TiO₂) are recognized as attractive energy materials applicable for lead halide perovskite solar cells (PSCs). Sintering is one of the effective strategies for improving the carrier transport of semiconductor nanomaterials. Using the alternative metal-oxide-based ETL, nanoparticles are often used in a way that they are dispersed in a precursor liquid prior to their thin-film deposition. Currently, the creation of PSCs using nanostructured Sn/Ti oxide thin-film ETL is one of the topical issues for the development of high-efficiency PSCs. Here, we demonstrate the preparation of terpineol/PEG-based fluid containing both tin and titanium compounds that can be utilized for the formation of a hybrid Sn/Ti oxide ETL on a conductive substrate (F-doped SnO₂ glass substrate: FTO). We also pay attention to the structural analysis of the Sn/Ti metal oxide formation at the nanoscale using a high-resolution transmission electron microscope (HR-TEM). The variation of the nanofluid composition, i.e., the concentration of tin and titanium sources, was examined to obtain a uniform transparent thin film by spin-coating and sintering processes. The maximum power conversion efficiency was obtained for the concentration condition of [SnCl₂·2H₂O]/[titanium tetraisopropoxide (TTIP)] = 25:75 in the terpineol/PEG-based precursor solution. Our method for preparing the ETL nanomaterials provides useful guidance for the creation of high-performance PSCs using the sintering method.

An all-solid-state photo-rechargeable battery based on Cs3Bi2I9

Here, we present a new two-electrode photo-rechargeable FTO/TiO₂/Cs₃Bi₂I₉/Pt/FTO system. The key material is the photoactive lead-free perovskite Cs₃Bi₂I₉, which performs photoelectric conversion and provides energy storage. This study is the first example of a battery system in which charging and discharging are based on bismuth redox chemistry. In the photo-charged state, the fabricated battery has an open-circuit voltage of ∼0.28 V in the dark. With a series-connected pack of these batteries, an LED was lit for tens of seconds in the dark.

Photorechargeable Hybrid Halide Perovskite Supercapacitors

Current approaches for off-grid power separate the processes for energy conversion from energy storage. With the right balance between the electronic and ionic conductivity and a semiconductor that can absorb light in the solar spectrum, we can combine energy harvesting with storage into a single photoelectrochemical energy storage device. We report here such a device, a halide perovskite-based photorechargeable supercapacitor. This device can be charged with an energy density of 30.71 W h kg^-1 and a power density of 1875 W kg^-1. By taking advantage of the semiconducting and ionic properties of halide perovskites, we report a method for fabricating efficient photorechargeable supercapacitors having a photocharging conversion efficiency (η) of ∼0.02% and a photoenergy density of ∼160 mW h kg^-1 under a 20 mW cm^-2 intensity white light source. Halide perovskites have a high absorption coefficient, large carrier diffusion length, and high ionic conductivity, while the electronic conductivity is improved significantly by mixing carbon black in porous perovskite electrodes to achieve efficient photorechargeable supercapacitors. We also report a detailed analysis of the photoelectrode to understand the working principles, stability, limitations, and prospects of halide perovskite-based photorechargeable supercapacitors.

Photoelectrochemical energy storage materials: design principles and functional devices towards direct solar to electrochemical energy storage

Advanced solar energy utilization technologies have been booming for carbon-neutral and renewable society development. Photovoltaic cells now hold the highest potential for widespread sustainable electricity production and photo(electro)catalytic cells could supply various chemicals. However, both of them require the connection of energy storage devices or matter to compensate for intermittent sunlight, suffering from complicated structures and external energy loss. Newly developed photoelectrochemical energy storage (PES) devices can effectively convert and store solar energy in one two-electrode battery, simplifying the configuration and decreasing the external energy loss. Based on PES materials, the PES devices could realize direct solar-to-electrochemical energy storage, which is fundamentally different from photo(electro)catalytic cells (solar-to-chemical energy conversion) and photovoltaic cells (solar-to-electricity energy conversion). This review summarizes a critically selected overview of advanced PES materials, the key to direct solar to electrochemical energy storage technology, with the focus on the research progress in PES processes and design principles. Based on the specific discussions of the performance metrics, the bottlenecks of PES devices, including low efficiency and deteriorative stability, are also discussed. Finally, several perspectives of potential strategies to overcome the bottlenecks and realize practical photoelectrochemical energy storage devices are presented.

Photoirradiation-Induced Capacitance Enhancement in the h-WO3/Bi2WO6 Submicron Rod Heterostructure under Simulated Solar Illumination and Its Postillumination Capacitance Enhancement Retainment from a Photocatalytic Memory Effect

Recently, photoassisted charging has been demonstrated as a green and sustainable approach to successfully enhance the capacitance of supercapacitors with low cost and good efficiency. However, their light-induced capacitance enhancement is relatively low and is lost quickly when the illumination is off. In this work, a novel active material system is developed for supercapacitors with the photoassisted charging capability by the decoration of a small amount of Bi₂WO₆ nanoparticles on an h-WO₃ submicron rod surface in situ, which forms a typical type II band alignment heterostructure with a close contact interface through the co-sharing of W atoms between h-WO₃ submicron rods and Bi₂WO₆ nanoparticles. The photogenerated charge carrier separation and transfer are largely enhanced in the h-WO₃/Bi₂WO₆ submicron rod electrode, which subsequently allows more charge carriers to participate in its photoassisted charging process to largely enhance its capacitance improvement under simulated solar illumination than that of the h-WO₃ submicron rod electrode. Furthermore, the h-WO₃/Bi₂WO₆ submicron rod electrode could retain its photoinduced capacitance enhancement in the dark for an extended period of time from the photocatalytic memory effect. Thus, our work provides a solution to the two major drawbacks of reported supercapacitors with the light-induced capacitance enhancement property, and supercapacitors based on active materials with the photocatalytic memory effect could be utilized in various technical fields.