Silicon-based are extensively used as photovoltaic cells. In the fabrication process of a solar cell, it is necessary to introduce doping in one or more silicon layers. This involves the addition of impurities to generate n-type or p-type semiconducting layers. The majority carriers of p-type are holes, and n-type layers are electrons, respectively. Photovoltaic cells are prepared by arrangement of a doped p-type layer close to an n-type layer. Electrons and holes are in motion within the layers, creating an internal electric field. When light interacts with a photovoltaic cell, the incident light energy is absorbed, leading to the excitation of electrons and the subsequent generation of electron and hole pairs. The excited electrons in the conduction band move towards the n-type layer and the corresponding hole to the p-type layer, resulting in the current in photovoltaic cells. The typical efficiency of these solar cells is approximately 20%, significantly influenced by the time and intensity of the light exposure (Mulligan et al., 2004; Baca et al., 2010; Bullock et al., 2016; Hwang et al., 2020). Most crystalline silicon (c-Si) solar cells separate photogenerated electrons and holes using doped homojunction.

However, homojunction can lead to issues such as loss in the optics, problems with carrier transport, non-generation of hole and electron due to parasitic absorption, and undesired recombination such as Auger recombination, (Kim J. et al., 2021). The technological obstacles in developing homojunction related to doping, such as elevated processing temperatures, limited contact fractions, removal of dopant glass, and isolation of junctions, can be mitigated by implementing designs incorporating asymmetric carrier-selective heterocontacts (Bullock et al., 2016). Carrier-selective heterocontacts achieve low resistance for a specific charge carrier while impeding the flow of the opposite charge carrier. Several processes can generate carrier-specific heterocontact, including passivating layers on the surface and stacks that introduce asymmetry in the conductivity through creating band offsets, tunnelling effects, or band bending in crystalline silicon (c-Si). The silicon heterojunction cell architecture (SHA) has demonstrated superior efficiency to its homojunction counterpart, achieving the record for crystalline silicon (c-Si) solar cells in 2014 (Bush et al., 2017). Fabrication of asymmetric heterocontacts persistently depends on doped-silicon layers, which necessitate intricate depositions incurring parasitic optical losses. Further developments in the asymmetric carrier-selective heterocontact involve completely substituting doped-silicon layers with alternative materials like amorphous silicon to overcome the inherent limitations and practical challenges associated with doped silicon layers.

The work by (Kabir et al., 2018) proposed a strategy for the large-scale fabrication of foldable and flexible crystalline silicon solar cells by introducing cracks in the wafers. These wafers have a pyramidal structure on the surface to reduce the surface reflectance and increase the optical path length of the incident light. The cracks in the wafers are initiated at the sharp channels located between surface pyramids within the peripheral area of the wafer. The malleability of silicon wafers can be enhanced by reducing the sharpness of the pyramidal structure in the peripheral regions. Incan h et al. (Hwang et al., 2020) employed a random inverted-pyramidal polydimethylsiloxane (RIP-PDMS) film to achieve efficient photon control on thin c-Si solar cells, resulting in an efficiency of 24%. The thin c-Si solar cells, when combined with RIP-PDMS sheets, exhibit a notable 85.4% enhancement in integrated photon flux compared to the unmodified thin c-Si solar cells with a photon flux of 75.0%. The RIP-PDMS films showed light absorption within the wavelength range of 300 to 1,100 nm, leading to a notable increase in efficiency by 17.3% compared to the identical device lacking the film. The efficiency of heterojunction with intrinsic thin layer (HIT) c-Si solar cells with RIP-PDMS sheets is 18.4%. The utilisation of thin c-Si flexible solar cells in conjunction with RIP-PDMS optical films has demonstrated remarkable stability when bending, establishing them as a viable and promising option for developing flexible solar cells with exceptional efficiency. The apparent drawback associated with the decreased lifetimes of minority carriers in the bulk material resulted in diminished sensitivity to longer wavelengths of light and a consequent decrease in short-circuit current. However, this negative effect was counterbalanced by the enhanced voltage. Several drawbacks are associated with silicon-based solar cell technology, including their high cost, substantial weight, limited availability of silicon resources, and production methods that result in significant environmental damage and ensuring cleanliness on the illuminated surface is of utmost importance.

Wearable electronics that use flexible solar cells rely less on traditional charging methods, alleviating users’ need to recharge their devices often. The ability to utilise ambient light as an energy source has enabled users to conveniently recharge their wearable devices while in motion, enhancing their self-sufficiency and diminishing reliance on conventional power sources.

Quantum dot solar cells rely on quantum dots as the primary material for absorbing light. Quantum dots refer to semiconductor particles at the nanoscale that possess distinctive optical and electrical characteristics due to the confinement of the excitons (Aroutiounian et al., 2001; Raffaelle et al., 2002; Kamat, 2008; Kamat, 2013; Kramer and Sargent, 2014). The bandgap of these materials can be adjusted by manipulating their dimensions, enabling light absorption across a broad spectrum of wavelengths (Chuang et al., 2015; Ramiro et al., 2015; Lu et al., 2019; Sharma and Jha, 2019; Mahajan et al., 2020; Nideep et al., 2020). When the dimensions of nanocrystals (NCs) approach or fall below the Bohr radius of the electron-hole bound state, commonly referred to as an exciton, the spatial mobility of electrons and holes becomes limited. Consequently, the energy levels of electrons and holes become discretised. A direct relationship exists between the magnitude of the band gap and the dimensions of quantum dots (QDs), whereby an increase in the band gap corresponds to a decrease in the size of the QDs (Lu et al., 2020a; Sun et al., 2023; Zhao et al., 2023). These materials’ optical and electrical properties are altered due to quantum confinement effects. Using near-infrared (NIR)-absorbing quantum dots (QDs) expands the absorption range in the near-infrared spectrum. Quantum dots (QDs) exhibit a lower photon energy threshold required for generating multiple excitons than perovskites, conventional bulk semiconductors, and organic semiconductors (Chang et al., 2013; Carey et al., 2015; Yang et al., 2020). This characteristic enables quantum dot photovoltaics (QDPVs) to exceed the theoretical efficiency SQ limit. Due to spatial confinement, the Coulomb potential significantly influences the interaction between electron-hole pairs in free-standing quantum dots (QDs). This strong interaction enables the persistence of these pairs as excitons rather than as free carriers. The formation of free carriers can only occur when the excitons dissociate (Hou et al., 2020; Efros and Brus, 2021; Han et al., 2022). Quantum dots (QDs) have the potential to enhance the efficiency of electron-hole pair multiplication mechanisms by effectively utilising excess photon energy to generate additional electron-hole pairs, hence preventing its dissipation as thermal energy (Ikeri et al., 2021; Liu et al., 2022). Numerous electron-hole pairs, or excitons, can be generated from the absorption of a single photon through a phenomenon known as “quantum dot super fluorescence” (Lu et al., 2020b). Meanwhile, the considerable tunability of the bandgap exhibited by quantum dots facilitates effective energy capture throughout the near-to-short-wave infrared region of the solar spectrum.

Nevertheless, the current efficiency of Quantum Dot Photovoltaic (QDPV) in 1 Sun condition is lower when compared to Organic Photovoltaics (OPVs) and perovskite solar cells. This discrepancy primarily arises from the intricate synthesis process of the materials involved and the formation of defect states during the device’s construction. QDPVs generally exhibit a lower power conversion efficiency (PCE) of approximately 13% compared to OPVs and PPVs under standard one Sun conditions. However, QDPVs can attain superior device performance under low light settings owing to their significantly higher bandgap (Mishra et al., 2022). The band gaps of quantum dots (QDs) can be readily adjusted by manipulating their diameters due to the quantum confinement effect, rendering them desirable for solar cell applications. Approximately 50% of the solar irradiance is concentrated within the near-infrared (NIR) region, which remains largely not absorbed by dye molecules and organic semiconductors (Zampetti et al., 2019). The capture of near-infrared (NIR) photons gives a significant opportunity to enhance the efficiency of QD solar cells. PbS and PbSe have garnered considerable interest and have been extensively employed in thin-film solar applications due to their tiny band gap, often ranging from 1.4 to 0.8 eV or even below (Hu L. et al., 2019). Despite their considerable potential, quantum dot solar cells for wearable devices still encounter several hurdles. Considering stability and durability is crucial to guarantee sustained performance across various environmental conditions. Furthermore, the cost-effectiveness of quantum dot synthesis and fabrication would significantly contribute to their widespread utilisation in wearable applications.

It is anticipated that the efficiency and performance of QDSCs will be enhanced through the progress made in quantum dot technology and the implementation of novel fabrication methods. The ongoing development of wearable electronics has sparked interest in the potential of quantum dot solar cells to significantly transform the power supply infrastructure and facilitate the widespread integration of eco-friendly wearable technology. Quantum dot solar cells can be developed using colloidal synthesis, chemical bath deposition, inkjet printing, and vacuum-based techniques like molecular beam epitaxy or sputtering (Giménez et al., 2009; Yang et al., 2017; Das et al., 2019; Liu et al., 2020). The manufacturing process of QD solar cells involves the application of quantum dots onto a substrate, usually accomplished by a step-by-step assembly process and their integration into a device structure alongside a suitable charge transport layer. Quantum dot solar cells have demonstrated significant absorption coefficients, facilitating effective light capture. These solar cells can exceed the Shockley-Queisser limit (Semonin et al., 2012), establishing the upper-efficiency limit for traditional single-junction solar cells. Power conversion efficiency that has surpassed the threshold of 12% is exhibited by Quantum dot solar cells (Hu et al., 2021). Quantum dot solar cells can be used in portable electronics, low-light environments, and building-integrated photovoltaics, including flexible and transparent energy solutions (Huang et al., 2022; Riaz and Park, 2022; Kim et al., 2023). Integration of multiple solar cell technology in tandem can potentially be used to improve performance.

The tunability of the band gap in quantum dots (QDs) enables the optimisation of single-junction solar cells by varying the size of QDs. The highest power conversion efficiency of 31% was predicted theoretically by Shockley and Queisser for the single-junction, non-concentrated solar cells with a semiconductor as an absorber with an ideal band gap of 1.1 eV (Chen et al., 2021; Kamaraki et al., 2021). This band gap restriction imposed by the theoretical model significantly narrows down the range of semiconductors suitable for developing ideal photovoltaics for wearable applications. To mitigate this constraint, low-band-gap quantum dots (QDs) such as PbS and PbSe QDs can be used (Luo et al., 2019; Nishimura et al., 2019). The studies by Beard and others (Gao et al., 2011) found a correlation between the size of quantum dots (QDs) and the photoconversion efficiency of PbS/ZnO solar cells. The precise value band gap did not mention their work. Liayang’s team (Chang et al., 2013) has obtained greater efficiency for PbSQDs with a band gap of 1.33 eV. The band gap value mentioned by Liayang’s team is close to the theoretical values calculated by (Carey et al., 2015). The research conducted by Sargent et al. focused on investigating the photovoltaic performance of p-n heterojunction solar cells with PbS quantum dots (QDs) and titanium dioxide (TiO₂) junction. The study involved QDs with three diameters, 3.7nm, 4.3 nm and 5.5nm, corresponding band gaps of 1.3 eV, 1.1 eV, and 0.9 eV. It was observed that the optimal band gap for achieving the highest performance was 1.3 eV, as indicated by the most significant values for open-circuit voltage (VOC), short-circuit current density (ISC), fill factor (FF), and power conversion efficiency (PCE).

The performance of solar cells is also influenced by the architecture of the solar cell devices apart from light absorption. Multiple layers of quantum dots with varying sizes can be used to enhance photon collection efficiency through a broader spectrum of wavelengths. This strategy aims to substantially augment the overall efficiency of the photovoltaic cells for indoor applications (Yang et al., 2020). According to theoretical predictions, the efficiency of tandem (double-junction) and triple-junction cells is expected to surpass the Shockley limit of 31%, reaching 42% and 49%, respectively (Hu Y. et al., 2019; Gan et al., 2021). The commercialisation of these solar cells has been limited due to the expensive manufacturing process and the requirements for close lattice matching between different semiconductor materials in various layers. While the concept of epitaxial compound semiconductor thin films has been successfully demonstrated, its widespread implementation has been impeded. Utilising size-tunable quantum dots (QDs) could potentially facilitate the production of these multijunction cells and the synthesis of photoactive materials (Z et al., 2022). Recent development in tandem QD cells involves the introduction of a graded recombination layer (GRL) positioned between junctions. The GRL layer connects the junctions and improves the flow of charge carriers by reducing the energetic barrier between the front and back cells in tandem multijunction photovoltaics (Wang et al., 2011). The tandem quantum dot (QD) solar cells use a front cell made of a quantum dot layer with an energy bandgap of 1.6 electron volts (eV), while the back cell consists of a quantum dot layer with an energy bandgap of 1.0 eV. The study lays the groundwork for utilising multijunction solar cells in wearable applications.

Huang et al. (Huang et al., 2011) reported a novel strategy to fabricate flexible solar cells utilising CdS/CdSe quantum dots. A photoanode with varied thickness was incorporated with CdS/CdSe quantum dots (QDs) to achieve flexibility. The highest current density achieved was 12.3 J/mAcm^-2, with an efficiency rating of 87%. This photovoltaic facilitates easy integration with wearable devices. Quantum dot solar cells are an alternative to conventional solar cells in wearable technology due to tunable characteristics such as enhanced light-capturing abilities, small dimensions, and adaptability (Figure 2). Several materials, such as cadmium selenide (CdSe), lead sulfide (PbS), and perovskite minerals, can make quantum dots. This material variety makes it possible to customise QDSCs to meet the needs of particular applications (Table 1). Many quantum dot materials, like those made of cadmium, are toxic and cause environmental and human health problems during manufacture, use, and disposal. More importantly, due to substantially higher production and application costs, large-scale manufacturing of QDs may not be possible. Their widespread use in real-world applications is therefore constrained. Some QDSCs include hysteresis effects, where the direction of the voltage sweep affects the output current-voltage characteristics. These factors may hamper the design and control of QDSCs.

Dye-sensitised solar cells (DSSCs) have garnered considerable interest from both academic and industrial sectors due to their production cost-effectiveness, compact structural design, and efficient power conversion capabilities across varying light intensities. DSSCs utilise organic dyes as photosensitisers and semiconductors to convert light to electrical energy. In 1991, O'Regan and Grätzel (Aslam et al., 2020) reported the development of Ruthenium dye-sensitised solar cells (DSCs) that used wide band gap titania semiconducting film with an efficiency of 7.12%. This advancement marked the commencement of a novel phase in photovoltaic (PV) research, and a remarkable achievement of 13% PCE was obtained under AM1.5 light conditions (Sun and Sariciftci, 2017). Dye-sensitised solar cells (DSCs) exhibit notable attributes such as optical clarity, a wide range of colour options, resistance to variations in lighting conditions, affordability, and straightforward manufacturing processes (Baxter et al., 2009; Bari, 2014; Meddeb et al., 2022).

Furthermore, these solar cells exhibit comparatively more flexibility and low weight, depending upon the specific substrate employed. Due to these distinctive characteristics, dye-sensitised solar cells (DSCs) are well-suited as a power source for wearable sensor modules and other applications such as building-integrated photovoltaics (BIPV), automotive-integrated photovoltaics (AIPV), as well as portable and interior power producers (Ito et al., 2008; Alnoman et al., 2022). The photo-electrode requires flexible substrates with crucial characteristics such as transparency and conductivity. This is because the dyed semiconducting film, such as TiO₂, responsible for capturing incident light and facilitating the passage of photoelectrons, is directly affixed to the substrate (Shankar et al., 2009; Friesen, 2013). Besides ruthenium complex dye, porphyrin and organic dyes showed power conversion efficiencies (PCEs) of 13% and 14.7%, respectively (Koteshwar et al., 2022). Nevertheless, using liquid electrolytes (LEs) may lead to leakage and vaporisation, diminishing the overall long-term robustness of dye-sensitised solar cells (DSSCs). Replacing liquid electrolytes (LEs) with solid-state and polymer gel electrolytes has enhanced the long-term durability of dye-sensitised solar cells (DSSCs). However, this substitution has also led to a decrease in their power conversion efficiencies (PCEs). The Internet of Things (IoT) has garnered considerable attention in science and technology due to its applications in several domains, such as smart homes, agriculture, healthcare, transportation, and industry. Dye-sensitised solar cells (DSSCs) are considered highly suitable energy sources for Internet of Things (IoT) devices due to their ability to convert indoor light into electrical energy without the need for further energy input (Chen et al., 2017; Yoo et al., 2020; Kokkonen et al., 2021).

Wearable photovoltaic-powered textiles with good stretchability were fabricated by (Yang et al., 2014), utilising electrically conducting elastic fibers. The fiber electrodes were initially manufactured by wrapping aligned multi-walled carbon nanotube (MWCNT) sheets around rubber fibres with excellent and consistent electrical characteristics when stretching. A Titanium wire that had been modified was utilised as the working electrode and subsequently twisted onto the elastic MWCNT fiber. This was followed by applying photoactive chemicals to create a wire-shaped dye-sensitised solar cell (DSC). The wire-shaped dye-sensitised solar cells (DSCs) were ultimately integrated into the intended stretchable and wearable photovoltaic cloth. The dye-sensitised solar cells (DSCs) used in this study exhibited notable energy conversion efficiencies of 7.13%, which were effectively sustained even when subjected to stretching. Most DSSC substrates are made of plastic and have a low thermal processing limit of about 150 °C. Low-temperature processing reduces semiconductor film adherence to the substrate and results in poor electrical contact between semiconductor particles when plastic substrates are used. Compared to conventional silicon-based solar cells, DSSCs have the potential for cheaper manufacturing costs. The manufacturing techniques and the cost of the raw materials are frequently lower. Due to their low manufacturing costs, simplicity in construction, and customisable optical characteristics, such as colour and transparency, dye-sensitised solar cells have attracted much attention recently.

Perovskites have a crystalline structure resembling calcium titanate (CaTiO₃) that has shown potential for developing high-performance solar cells with low production costs (Li et al., 2020). Recently developed solid-state solar cells based on inorganic-organic light-absorbing halide perovskites have shown great promise in wearable/portable devices (Kim et al., 2015; Lee et al., 2019). This is due to their economically and practically feasible fabrication processes involving low temperatures and the roll-to-roll technique. The band gap of perovskites can be altered by changing the chemical composition and achieve a broader photon absorption efficiency (Akin et al., 2020). This tunability of the band gap is one of the crucial requirements for selecting the photovoltaic power sources for wearable sensor modules, as the PVs should be able to absorb light from different light sources even during indoor conditions. These solar cells exhibit a high-power conversion efficiency (PCE) exceeding 16%, further highlighting their potential as leading candidates in the wearable technology domain (Chen et al., 2019). Numerous research groups have recently attempted to develop flexible perovskite solar cells by utilising an all-low temperature manufacturing process operating at approximately 1,300 ^°C. Preliminary findings from these studies indicated that such perovskite solar cells may exhibit superior efficiency compared to flexible organic solar cells. The flexible perovskite solar cells employed two distinct light absorbers, namely, CH₃NH₃PbI₃ and CH₃NH₃Pb ^I05 . The current highest power conversion efficiency (PCE) achieved by flexible perovskite solar cells is 10.2%, in which a layer with a thickness of 300 nm is used as a light absorber (Liu and Kelly, 2014). However, this value remains lower than that of rigid-type perovskite solar cells. This comparatively lower PCE is attributed to series resistance and rapid charge recombination during quick charging.

Nevertheless, these challenges can be addressed by improving the charge collection layer, specifically the TiO₂ or ZnO compact layer, on the flexible substrate (Du et al., 2018). Perovskite solar cells are an innovation with excellent power conversion efficiency. These cells can be placed onto flexible substrates like PET or PEN for wearable applications. Flexibility and cost-effectiveness make perovskite-based devices attractive for wearable technologies. There exist three primary impediments that hinder the widespread commercialisation of PSCs. To begin with, it is imperative to address the inherent issue of low stability exhibited by the perovskite material, as this poses a significant obstacle in attaining sustained and reliable power output over an extended period. Additionally, it is necessary to implement measures to regulate and supervise the hazardous Pb²⁺ waste and contamination resulting from the irreversible degradation of perovskite materials. Furthermore, it is imperative to enhance the performance of PSCs to address the requirements of extensive production and real-world applications effectively. To address these challenges, valence state substitution can be employed to select non-toxic elements that meet the required criteria.

Perovskite solar cells exhibit significant potential in providing energy for wearable devices due to their advantageous characteristics, including higher efficiency, reduced weight, and enhanced flexibility. Perovskite solar cells are anticipated to significantly impact the future of wearable technology since ongoing research addresses issues about stability, toxicity, and manufacturing scalability. The capacity of energy harvesting technologies to offer a durable and adequate power supply for wearable devices has the potential to bring about a transformative impact on how we engage with and utilise such gadgets. This, in turn, could facilitate the development of more sophisticated and ecologically conscious wearable technology. The potential of perovskite solar cells to transform the landscape of wearable technology is evident by their continuous advances and increasing commercialisation (Figure 3).

These solar cells integrate organic and inorganic materials to exploit the respective benefits of each component. The organic components have the advantages of flexibility and cost-effectiveness in processing, whilst inorganic components contribute to enhanced stability and increased efficiency (Sharma et al., 2014). Various fabrication techniques can produce organic and inorganic hybrid solar cells, such as solution processing, vacuum deposition, and spin-coating procedures (Fan et al., 2013). The fabrication entails integrating organic and inorganic elements into a device structure, commonly achieved using layer-by-layer assembly or bulk heterojunction methodologies (Huang et al., 2010). Hybrid solar cells derive advantages from the synergistic characteristics exhibited by organic and inorganic materials. Organic materials show flexibility, lightweight nature, and tunable light absorption (Wright and Uddin, 2012). Conversely, inorganic materials display desirable attributes such as stability, fast charge mobility, and a wider variety of absorption capabilities. The interface between organic and inorganic materials facilitates the effective transfer and separation of charges, enhancing device performance. Several studies have found power conversion efficiencies over 15% in organic and inorganic hybrid solar cells, indicating their significant potential in this field (Wright and Uddin, 2012; Khan et al., 2019; Zhang et al., 2021; Zhao et al., 2021).

Organic photovoltaics (OPVs) are prevalent in wearable technology due to their flexibility and lightweight. OPVs can stretch and conform to the wearer’s movements when made on elastomeric substrates like PDMS or polyurethane. Recent OPV technological improvements have increased efficiency and durability, making them a feasible wearable energy harvesting option. One notable advantage of these solar cells is their ability to demonstrate a broader absorption spectrum than conventional organic or inorganic solar cells, facilitating improved light capture. Hybrid solar cells exhibit versatility in their applicability, including a diverse array of uses such as portable electronic gadgets, solar-powered apparatuses, and integration into the architecture of buildings. Due to their ability to be produced on flexible substrates, organic-inorganic hybrid solar cells are well suited for use in flexible electronics and wearable technologies. With values above 25%, organic-inorganic hybrid solar cells have displayed impressive power conversion efficiency. The distinctive optoelectronic characteristics of perovskite materials are credited with this efficiency. One of the significant perplexing problems seen in perovskite photovoltaics is abnormal hysteresis observed in the current-voltage response of HPSCs. Such hysteresis phenomena could result in inaccurate calculation of the solar cell device’s efficiency, which calls into question its dependability. This poses a significant barrier to advancement from both a research and commercialisation perspective. Flexible and transparent solar cells can be used to integrate into a wide range of substrates and surfaces. Hybrid solar cells exhibit potential for application in promising technologies, including wearable electronics and Internet of Things (IoT) devices.

The scientific progress in the field of indoor photovoltaic (IPV) did not experience significant momentum until the year 2010. The present surge in research activity about IPV can largely be attributed to the advancements in IOT and wearable devices. Recently, indoor lighting tends to LED and FL bulbs, deemed more aesthetically pleasing and efficient than incandescent lights (Kim et al., 2022; Ding et al., 2023). Many sensor nodes within the swiftly growing IoT network, which rely on a power source for operation, exist. The main components of an IOT are sensors, actuators, electronics, storage units/memory devices, and communication units (Asemani et al., 2019). Notably, most of these nodes are situated within indoor structures. Due to technical progress, many IoT components’ energy consumption has significantly decreased. However, a significant obstacle to adopting the IoT ecosystem will be providing power to the billions of newly connected IoT devices. Simultaneously, the market for wireless sensors is experiencing growth due to the emergence of novel low-power network protocols incorporating energy-saving capabilities, such as radio frequency (RF) backscatter technology, Zigbee, BLE, Sigfox, and others. The global value of the IPV cell market is projected to reach up to $850 million by the year 2023 (Mathews et al., 2019). Although the current market share of the IPV sector in the global solar module industry is very tiny, estimated at less than 1%, its growth trajectory is expected to be rapid owing to its potential for specialised applications. The market for IPV is projected to experience a significant growth rate of 70% compounded annually, primarily propelled by the surge in the IoT market.

Operating the large PV cells outdoors is vital for supplying energy to the electrical grid and powering household appliances. Despite the notable disparity in light intensity and resulting power generation between indoor and outdoor environments, it is possible to incorporate product-integrated photovoltaics (PIPVs) into various wearable devices. These PIPVs can function at deficient power levels, ranging from 1 mW to 100 mW, and continuously harness the accessible indoor light (Jegadeeswari and Rekha, 2020). A wide range of gadgets, such as wearable devices like smartwatches, computers, remote controls, health monitoring devices, RFID tags, Bluetooth, and other PIPVs in diverse manners. The predominant proportion of (IoT) devices that operate on IPV are characterised by their autonomous configuration, indicating that they are not linked to a centralised power grid. An appealing product alternative is achieved by integrating flexible IPV cells with wearable devices. This capability enhances battery longevity and reduces the expenses associated with battery replacement and upkeep. Due to their ability to facilitate the integration of IPV cells across various applications, they possess a high level of appeal. The crucial elements in this context are lightweight, cost-effective, and exceptionally versatile solution-processable photovoltaic technology. Present-day structures such as residential buildings, commercial establishments, and corporate spaces are eliminated using artificial illumination, a potential photon-capturing source by indoor photovoltaic cells. This practice persists even in instances where natural light, either direct or indirect, may be readily available within interior settings during daylight hours. Different artificial illumination sources include incandescent lighting, halogen bulbs, compact fluorescent lamps (CFL), and light-emitting diode (LED) bulbs (Min et al., 2023).

Furthermore, apart from possessing unique designs and applications, each of these diverse light sources exhibits a distinct emission spectrum. The range of interior lights predominantly encompasses the visible light spectrum, which ranges from 400 to 700 nm. In contrast, the AM 1.5G solar spectrum contains a significantly broader range of wavelengths, extending from 300 to 2,500 nm (Park et al., 2022). Moreover, indoor light sources’ spectral irradiance exhibits significant disparities compared to natural sunlight. Indoor light sources often show intensities 100 to 1,000 times lower than the typical solar radiation of 100 mW cm² or AM 1.5G (Huang et al., 2021). Illumination refers to the total quantity of light incident upon a particular surface or region. Lighting levels in indoor areas often vary between 100 and 1,000 lux (Kumar and Chen, 2023). In contrast to the external environment, the absence of a standardised approach for assessing the indoor performance of solar cells is evident when the “standard one Sun condition” is considered (Lübke et al., 2021).

The characterisation of indoor performance often involves utilising an illuminance level ranging from 200 to 1,000 lux. An illuminance level of 200 lux typically designates a dim interior environment, while a bright interior environment is denoted by an illuminance level of 1,000 lux (Muhammad et al., 2022). The energy collected by photovoltaic cells from different light sources has fluctuated due to their diverse spectral response, even when subjected to the same illumination (Li et al., 2019; Zarrabi, 2023).

To achieve high efficiency, it is required to utilise photovoltaic materials with a wide bandgap due to the restricted range of the indoor light spectrum, which typically falls within the 400–700 nm wavelength range (Yue et al., 2020). According to Freunek et al., (Freunek et al., 2012), the range of 1.90–2.00 eV is considered the best bandgap for narrow-band artificial light sources, including LEDs and fluorescent tubes. The maximum efficiency of the interior light sources was determined by employing the Shockley-Queisser model for calculation. The highest efficiency obtained for fluorescent tubes, phosphorous white LEDs, sodium discharge lamps, and RGB white light is 67%, 45.7%, 47.70%, and 58.40%, respectively. The preferred bandgap values for fluorescent and sodium discharge lamps are 1.95 eV and 2.10 eV, respectively. The photovoltaic device demonstrates high performance in AM 1.5G conditions and may not exhibit optimal functionality in indoor lighting conditions. The spectrum emission of the two artificial illumination sources was significantly limited in the range above 620 nm, resulting in photon counts that exceeded the maximum power conversion efficiency (PCE) achievable by silicon (Si) photovoltaics under natural sunlight irradiation. To enhance the efficiency of solar cells, it is imperative to develop device designs tailored to the specific features of solar cells when exposed to indoor lighting sources, which are predominantly utilised in indoor environments. To efficiently capture energy from a particular light source, it is necessary to have an absorber layer that possesses semiconductor characteristics that are closely aligned. LEDs are anticipated to become the dominant lighting technology owing to their exceptional color range, great luminosity, extended operational longevity, and superior energy economy. The output power of a PV device depends upon the intensity and spectrum of the indoor light source, size and orientation of the photovoltaic (PV) device, distance from the light source, and transparency. Both artificial lighting sources and diffused sunlight that enters through windows or facades can serve as potential light sources within a building (Venkateswararao et al., 2020). The selection of the most suitable photovoltaic (PV) material should depend upon the prevailing lighting conditions within the building, with the aim of maximising power generation.