Our world's rapid technological advancement, known as Industry 4.0, is transforming the energy sector. The increasing demand for electricity, coupled with environmental concerns, has driven us to shift from fossil fuels to cleaner renewable sources like solar and wind. However, maintaining consistent energy supply becomes a challenge due to the inherent variability of these sources. Here, Industry 4.0 comes to the rescue. Advanced technologies like smart grids and AI-powered forecasting are becoming crucial for managing renewable energy systems by optimizing distribution and predicting fluctuations. Among renewables, solar power emerges as the frontrunner for its immense, long-term potential, surpassing other sources in terms of cleanness, reliability, and global availability. The prime focus of designing a solar structure is to produce electricity. Apart from this, solar energy has a wide range of applications across various domains like water and building heating, solar distillation (Abimbola et al., 2021; G. Ayoub et al., 2012; Xu et al., 2020). It proves to be cost-effective, as it can be constructed using readily available, affordable materials found locally, and it incurs minimal expenses for maintenance and operation.(G. M. Ayoub & Malaeb, 2014; Kabeel et al., 2020) Harnessing solar power for seawater desalination offers a viable solution to the worldwide scarcity of potable water. However, integrating energy storage solutions and implementing supportive policies are critical for a smooth transition to a sustainable future powered by renewables.
In the pursuit of sustainable and effective solar energy solutions, researchers are investigating a range of materials beyond conventional silicon to convert solar energy into usable power. The use of affordable, environmentally benign materials in solar cells is still a concern. The significant physical and chemical properties of perovskite inorganic metal halide compounds have garnered considerable attention, particularly in photovoltaics applications(M. A. Islam et al., 2023). The design of halide perovskites based on Pb has made it possible to achieve PCEs of 29.1%. (Best Research-Cell Efficiency Chart | Photovoltaic Research | NREL, n.d.) However, the stability issues with these Pb-based materials result in poor long-lasting performance, preventing the practical use of perovskite solar cells(PSCs). Hence, a challenging and crucial realm of research involves the exploration of appropriate solar cells materials. Due to their diverse chemical and physical characteristics, perovskites and materials resembling perovskite have been a focal point of comprehensive research for numerous years. The performance of the perovskite solar cell configuration has markedly improved because of employing these superior perovskite materials. A variety of inorganic and organic components are employed to synthesize the perovskite compounds. (Adjogri & Meyer, 2020) Moreover, owing to their diverse compositions and structures, these substances offer a wide-ranging foundation for material design using the standard ABX3 formula. In this framework, A and B denote various metal cations with positive charges, while X refers to a negatively charged anion, including fluorine (F1−), chlorine (Cl1−), bromine (Br1−), iodine (I1−), oxygen (O2−), sulfur (S2−), selenium (Se2−), and tellurium (Te2−).
It is also important to note that the Goldschmidt tolerance factor (t) and the octahedral factor (µ) are two significant parameters used to approximate the inclusion of appropriate cations to produce perovskite or perovskite like nature. Both the factors are dimensionless parameter and the function of iconic radii of the constituent elements(Goldschmidt, 1926) and can be expressed as following equations (Eqs. 1 and 2) –
\(t= \frac{{r}_{A}+{r}_{X}}{\sqrt{2}\left({r}_{B}+{r}_{X}\right)}\) ------- (1)
\(\mu =\frac{{r}_{B}}{{r}_{X}}\) ------ (2)
In this context, rA and rB refer to the radius of the larger-sized A and B elements or molecules, respectively, while rX denotes the radius of the smaller halide (Cl, Br, I) anion. For the establishment of robust perovskite architectures, the tolerance factor (t) is required to reside within the interval of 0.8–1.0. Correspondingly, the octahedral factor (µ) is necessitated to be confined within the range of 0.44–0.72, which is imperative for the stable formation of a BX6 octahedral coordination involving the B-site cation and X-site anion.(Yi et al., 2019) Goldschmidt's tolerance factor (t) has significantly influenced the advancement of perovskite materials (Kieslich et al., 2014) and used as the benchmark in the manufacturing of unique enduring hybrid perovskite configurations by adjusting the compositions. (Lee et al., 2015; Li et al., 2016; McMeekin et al., 2016; Q. Wang et al., 2019)
In the ongoing quest for a resilient and efficient perovskite material, scientists have identified a new category of semiconductor materials referred to as chalcogenide perovskites (CPs). These materials are attracting attention because they are both environmentally benign and non-toxic, while also having excellent properties for converting light into electricity. The chalcogenide perovskites (CPs) adhere to the stoichiometric formula ABX3, wherein A is designated as a cation from the group II elements (e.g., Ca2+, Sr2+, Ba2+), B is a transition metal cation from group IV (e.g., Ti4+, Zr4+, Hf4+), and X is an anion from the chalcogen group (e.g., S2-, Se2-). Recent investigations have delved into the potential of chalcogenide perovskites as a distinctive group of materials with higher bandgaps, suitable for employment as absorber layers in thin-film solar cell applications. (Adjogri & Meyer, 2021; Sopiha et al., 2022; Tiwari et al., 2021) These materials primarily made up with earth abundant elements, demonstrating remarkable chemical and thermal stability. (Niu, Milam-Guerrero, et al., 2018) Experimental findings have indicated promising optoelectronic properties, including exceptionally high absorption coefficients (Meng et al., 2016; Nishigaki et al., 2020)elevated photo-luminescence efficiencies (Hanzawa et al., 2019; Niu et al., 2017; Yang et al., 2022; Ye et al., 2022)moderately high carrier mobilities (Yu et al., 2021), and the capacity for chemical doping to generate both n-type and p-type semiconductors. (Hanzawa et al., 2019)
Earlier research has indicated that certain compounds, namely BaZrS3, SrZrS3, BaHfS3, SrHfS3, CaZrS3, and CaHfS3 exhibit a -kind structure with an optimal bandgap, making them well-suited for photovoltaic (PV) applications. (Akkerman & Manna, 2020; Meng et al., 2016; Nishigaki et al., 2020; Sun et al., 2015) Among these compounds, BaZrS3 has been extensively investigated due to its lead-free and excellent environmentally friendly properties. (Comparotto et al., 2020; Márquez et al., 2021; Wei et al., 2020; Yu et al., 2021) Additionally, BaZrS3 demonstrates notable features such as a high absorption coefficient (> 105 cm− 1), outstanding defect tolerance, and improved mobility of charge carriers. (Wei et al., 2020) Research by Y. Nishigaki et al. has highlighted the extraordinary absorption coefficient (α) of these compounds compared to other practical solar cell absorbers. BaZrS3's shallow light penetration depth (~ 100 nm) makes it a more approachable set of photo-generated carriers. (Nishigaki et al., 2020) The bandgap of BaZrS3 compounds, spanning roughly 1.7 to 1.9 eV, slightly exceeds the ideal bandgap range for single-junction solar cell design. Empirical evidence suggests that alloying strategies, notably the substitution of Ti at the Zr lattice sites and the inclusion of Se in place of S, can substantially modulate the bandgap. This modulation renders the material more suitable for the fabrication of single-junction PV devices. (Meng et al., 2016; Nishigaki et al., 2020; Sharma et al., 2021) Notably, substituting Ti and Se bring down the bandgap while maintaining a high absorption coefficient. These materials predominantly exhibit p-d electronic transitions, characterized by an elevated joint density of states relative to the p-p transitions observed in lead halide perovskites. Consequently, these compounds manifest a superior optical absorption coefficient in comparison to lead halide perovskites, facilitating the employment of thinner absorptive layers and possibly resulting in enhanced efficiencies vis-à-vis traditional lead halide perovskites.(Meng et al., 2016) The exploration of 2D Ruddlesden − Popper halogen perovskites, in comparison to their pure 2D or 3D counterparts, has attracted significant attention. These variants exhibit unique ambient stability while preserving exceptional system performance.(Chen, Yu, et al., 2018) BaZrS3's shallow light penetration depth makes it a more approachable set of photo-generated carriers.(Niu, Sarkar, et al., 2018)
Generally, achieving crystalline BaZrS3 thin films with the desired quality using traditional fabrication processes like pulsed laser deposition or DC sputtering, as well as chemical sulfurization of thin films (e.g., BaZrO3), may require temperatures between 700°C to 1000°C, which may have the presence of impurity phases in the obtained CPs compositions. (Comparotto et al., 2020; Márquez et al., 2021; Wei et al., 2020) Thus, low-temperature process development is necessary to fabricate solar devices at a reasonable cost while maintaining the desired bulk and interface properties. The process's multifaceted nature adds to the difficulty of this goal. Furthermore, the incompatibility of solvents with the extremely high temperatures required for BaZrS3 production makes it difficult to synthesize BaZrS3 thin films from a solution. Subsequently, the researchers engineered modifications to the surface chemistry of BaZrS3 nanocrystals, thereby rendering them amenable to colloidal dispersion in solvents with varying polarity, specifically N-methyl-2-pyrrolidinone (a polar solvent) and chloroform (a non-polar solvent). (Ravi et al., 2021) A separate study conducted by Z. Yu and colleagues showcased the creation of low-temperature (500°C) BaZrS3 CPs thin films through the alteration of the chemical reaction pathway. The results from this research suggest that lower temperatures lead to a decrease in sulfur vacancies and carbon impurities, which are commonly associated with higher temperature processes. (Yu et al., 2021) Accordingly, these insights pave the way for the facbrication of BaZrS3 CPs thin films at diminished thermal conditions, harboring prospects for the assembly of single or tandem photovoltaic apparatuses. Although, such high temperature processing requirements of BaZrS3 perovskite material make it a suitable candidate for heating applications as we have discussed earlier like desalination of sea water which is environmentally friendly approach to produce fresh water with low CO2 emissions.(Manchanda & Kumar, 2015)
Fundamentally, the architecture of perovskite solar cells incorporates a perovskite compound functioning as the absorptive medium, flanked by two charge transport layers. Within the realm of perovskite photovoltaics, TiO2 and Spiro-OMeTAD are predominantly utilized as the materials for transport of electrons and holes respectively. In this research work, a relative investigation has been conducted between the traditional TiO2 and Spiro-OMeTAD, and the relatively less explored gallium-doped zinc oxide (GZO) employed as the ETL, along with CuSbS2 serving as the HTL material. Electron Transport Layers (ETLs) are predominantly constituted of metal oxides, characterized by widespread bandgaps and optimal energy band alignment with the absorber layer. TiO2 stands out as the favored metal oxide ETL in perovskite solar cells (PSCs) owing to its apt bandgap and superior optical transmittance(Bin Rafiq et al., 2020; Sobayel et al., 2019). Nevertheless, TiO2's primary limitation lies in its inadequate solar light absorption capacity. Moreover, TiO2 exhibits relatively low electron mobility, quantified at 1 cm²/Vs.(Edri et al., 2014; Mahjabin et al., 2021, 2022) reducing its electrical conductivity accordingly. It is not economically feasible to get better electrical conductivity in TiO2 since doing so requires a high sintering temperature.(Mahjabin et al., 2021) Some substitutes exist, such as SnO2, which needs to be annealed at temperatures as high as 180°C. According to Ali et al., high temperature annealing presents difficulties for the future development of flexible PSCs in addition to complicating and raising the expense of PSC manufacturing. (Sobayel et al., 2018). Furthermore, SnO2 is readily oxidized to SnO4 and exhibits chemical instability. In contrast, ZnO exhibits a linear bandgap and a level of conductivity that is several magnitudes superior to that of TiO2. ZnO is a viable and affordable option for ETLs in modern applications since it can also reduce recombination losses in the device. Gallium-doped Zinc-oxide (GZO) is the result of the incorporation of gallium into ZnO, yielding a material characterized by exceptional optical transparency, elevated electrical conductivity, and a flexible fabrication process. GZO is regarded as a top contender for an Electron Transport Layer (ETL) to successfully handle the problems. The ZnO lattice structure is preserved upon substituting Zn2 + with Ga3+, as the covalent (1.26 Å) and ionic (0.62 Å) radii of gallium not only closely match those of zinc (covalent radius of 1.31 Å and ionic radius of 0.75 Å) (Lignier et al., 1997)but also the covalent bond length of GaO (1.92 Å) is comparable to that of ZnO (2.001 Å).(Mouchou et al., 2021) The application of metal conductive oxide-based ZnO, including Gallium-doped (GZO) or Aluminum-doped (AZO) ZnO films, has become increasingly prevalent in several sectors, notably in photovoltaic (PV) solar cells. This trend is attributed to their cost-efficiency, substantial storage capabilities, and eco-friendly attributes.(Chen et al., 2019; Raj et al., 2021) In this work, the GZO is utilized as the replacement of TiO2 layer.
Spiro-OMeTAD, recognized for its excellent hole mobility and stability, is commonly used as the hole transport layer (HTL) in perovskite solar cells (PSCs). Nevertheless, the deployment of Spiro-OMeTAD as an HTL presents certain challenges. One significant issue in fabricating perovskite solar cells is the high cost associated with the organic Spiro-OMeTAD used as a hole-transporting material. The complex manufacturing processes or high purity requirements is also a bottleneck for this pristine material.(Choi et al., 2014) Spiro-OMeTAD is characterized as hygroscopic, indicating its ability to absorb moisture from the air, thereby posing a risk of perovskite layer degradation and diminished device performance.(Zhao et al., 2020) Furthermore, the common practice of doping Spiro-OMeTAD with lithium salts to enhance conductivity can lead to issues over time, as these dopants may diffuse into the perovskite layer, contributing to device degradation.
Long-term stability is also a concern, potentially hindering the future commercialization of PSC due to cost and sustainability considerations when relying on organic hole conductors. Therefore, ensuring greater stability in the conductive components for holes is vital for the advancement of perovskite photovoltaics. In perovskite solar cells, p-type inorganic semiconductors are good choices for hole transport to measure hole conductivity. These materials stand out for having a variety of valence energy levels, high mobility, outstanding chemical stability, and remarkable visibility.(Rajeswari et al., 2017; H. Wang et al., 2017) However, Spiro-OMeTAD can be replaced with an alternate material for hole transport in PSCs. Currently, copper-based ternary chalcogenide semiconductors, delineated by the formula CuaBXb (with B being Sn, Sb, Bi and X being Se, Te, S), are under active research as novel p-type materials for thin-film solar cell applications.(Garza et al., n.d.; Van Embden & Tachibana, 2012) One of the most prevalent and affordable sulfides in nature is copper antimony sulfide (CuSbS2). CuSbS2 shows a direct bandgap of 1.5 eV (approx.) when compared to CuInS2. Furthermore, because the Sb element's ionic radius is comparable to that of In, it is more advantageous economically.(Zhou et al., 2009) Our recent work has demonstrated that the hot injection method may be used to readily manufacture CuSbS2 nanoplates and nanoparticles with desired photosensitive and mechanical features, leading to a consistent shape and size. (Moosakhani, Sabbagh Alvani, Mohammadpour, Ge, et al., 2018; Moosakhani, Sabbagh Alvani, Mohammadpour, Hannula, et al., 2018; Moosakhani, Sabbagh Alvani, Mohammadpour, Sainio, et al., 2018)