Recently, renewable energies have attracted more attention due to their clear advantages compared to traditional fossil fuels [1]. As a result, renewable sources of energy such as solar energy are becoming increasingly important in the global energy landscape [2,3]. To meet energy needs, solar cells are a suitable alternative to fossil fuels [1,[4], [5], [6]]. The ability of solar cells to effectively absorb photons from the sun's radiation depends on the electronic and optical properties of the semiconductor materials used as the absorber layer in the cell [7,8] and it has been determined that the optimized bandgap (Eg) for SJSCs falls within the range of 1.4–1.6 eV [8].

Based on experiments, it has been found that GaAs, which has a bandgap of 1.42 eV, is the material that demonstrates the highest efficiency in SJSCs [8]. GaAs materials have a direct bandgap, which allows for more efficient conversion of sunlight into electrical energy, as well as higher carrier mobility, which results in faster and more efficient movement of charge carriers within the cell. Additionally, GaAs cells can operate at higher temperatures and have a higher absorption coefficient compared to silicon [4]. As a result, GaAs-based solar cells have become a popular choice for many specialized applications where maximum efficiency and reliability are essential [9,10].

Metal-semiconductor contact can lead to rectified (Schottky) and ohmic junctions. In a Schottky junction, the electric field created in the depletion region of the semiconductor side turns it into a photovoltaic device. The combination of graphene and GaAs to make Schottky junction solar cells has recently garnered significant attention due to its simple and low-cost fabrication process [11,12]. Graphene, with its two-dimensional structure and unique properties such as high carrier density, mechanical strength, and optical transparency, has shown promise in the field of solar cell technology [13,14]. Single, double, and multi-layer graphene each have their own distinct applications and properties, and due to its extremely thin thickness, graphene allows for the transmission of a significant amount of light [[15], [16], [17], [18]]. Graphene is not only highly transparent, but it also serves as a carrier separation and collection layer in Graphene/GaAs Schottky junction solar cells [5].

Despite the many advantages of Graphene/GaAs solar cells, their efficiency was initially limited by a high surface recombination rate [5,15]. This problem was successfully addressed through the use of metal-insulator-semiconductor structured [19] or AlxGa1-xAs layers on the surface of the GaAs cell, which effectively passivate the surface and reduce recombination losses [5,20]. On the other hand, in Graphene/GaAs solar cells, recombination on the back surface can reduce efficiency. To mitigate this issue, very thin layers of heavily-doped material are applied to the back surface of the cell, which can effectively passivate the surface and by creating an electrostatic field reduce recombination losses [21]. Additionally, the presence of a minority carrier reflector layer on the back surface can help to increase light trapping inside the cell by making the light more disordered, further reducing recombination losses [8].

To achieve higher conversion efficiency, various types of solar cell configurations have been proposed [21,22]. One such configuration was developed by He et al. who designed a new structure for Schottky junction Graphene/GaAs solar cells. This structure included a hole transport layer (HTL), Graphene doping, and a TiO2 antireflection layer, resulting in improved performance compared to traditional designs [12]. The importance of minority carrier reflector layers in GaAs-based solar cells was recognized in the 1980s, leading to extensive research in this field. These layers can be added to the cell structure either by using a heavily-doped GaAs layer or an AlxGa1-xAs layer, with an appropriate value of x typically ranging from 0.2 to 0.3 [23]. A study of the crystal parameters of AlxGa1-xAs and GaAs has shown that despite having a small number of defects and recombination centers, they have similar crystal properties [24]. Additionally, the use of InAlGaP materials in the same cell configuration has been shown to increase efficiency due to their high photogeneration rate [25]. In the 1990s, InGaP emerged as a mainstream photovoltaic material due to its advantageous properties. One of the principal advantages of InGaP was its inviolability to oxygen pollution, which can have detrimental effects in AlGaAs alloys. In addition, InGaP has a lattice-compatible composition with GaAs, specifically In0.5Ga0.5P, which has a bandgap value that is well-suited for photovoltaic applications. InGaP layers have been suggested as window and back surface field (BSF) layers in single-junction GaAs-based solar cells due to their advantageous properties. The high electron mobility of InGaP (3500 cm2/V.s) increases the probability of carrier collection in the depletion region of solar cells, leading to high efficiency [26]. Gao et al. fabricated triple junction solar cells by using an InGaP layer and an AlGaAs layer as the back surface field layer in the GaInAs mid-subcell, respectively. While the InGaP layer acted as a prominent minority carrier reflector, it also led to a non-negligible increase in device series resistance, whereas the AlGaAs layer showed superior performance in terms of series resistance and minority carrier reflection [27]. Singh and Sarkar investigated the suitability of two important materials, InAlGaP and AlGaAs, as a substitute for the InGaP layer in an InAlGaP/GaAs tandem solar cell. They found that InAlGaP, with its wide bandgap, is a better choice for the back surface field layer than other commonly used Al0.7Ga0.3As materials. Additionally, Burnett et al. have shown that AlGaAs is highly sensitive to water pollution and oxygen, making it an undesirable choice for use in solar cells [24]. Galiana et al. conducted an experimental and simulation-based analysis of three different configurations of back surface field layers, namely p++-GaAs, p++-AlGaAs, and p+-InGaP, in a n/p junction GaAs solar cell. They found that while p++-GaAs back surface field layers have a weak reflection of minority carriers, they show very low series resistance. The p+-InGaP back surface field layers behave as excellent reflectors for minority carriers but involve a non-negligible increase in device series resistance due to unfavorable heterojunction. Finally, the p++-AlGaAs back surface field layers showed superior performance in terms of both series resistance and minority carrier reflectivity [23].

Experimental optimization of solar cells is often difficult due to their high cost, complexity, and time-consuming nature. Simulation is a useful tool for optimizing solar cell designs and understanding physical phenomena and electrical behaviors, as it can reduce time and save money [24,28]. In this study, we used Silvaco ATLAS to design a Graphene/AlGaAs/GaAs Schottky junction solar cell by adding different hole reflector (HR) layers. By simulating the physical and electrical behavior of the solar cell, we were able to optimize its performance and gain insights into the underlying mechanisms driving its behavior. The simulation results indicate that the use of InAlGaP as the HR layer in the Graphene/AlGaAs/GaAs heterojunction Schottky solar cell leads to improved performance, with JSC = 24.94 mA/cm2, VOC = 0.74 V, FF = 84%, and η = 15.6%, compared to the use of AlGaAs and InGaP materials. These findings suggest that the use of InAlGaP as an HR layer in solar cell designs may lead to improved efficiency, and could be a promising avenue for future research.