This work modelled and analysed perovskite solar cells based on Cs₂AgBiBr₆ with various electron transport layers and hole transport layers. The device structure is fluorine-doped tin oxide (FTO)/ZnO/Cs₂AgBiBr₆/NiO/Au. Power conversion efficiency (PCE) is practically saturated after the perovskite thickness of 700 nm. PCE declines from 21.88% to 1.58% when carrier lifetime decreases from 10³ ns to 10⁻¹ ns. Deep-level defects at mid-band gap energy of the perovskite layer can trap both carriers, allowing greater carrier recombination. Carrier capture cross-sectional area greatly impacts on cell performance. When subjected to high temperatures (T), the carrier mobility would diminish because carrier scattering increases cell resistance. That is why by raising T from 300 K to 400 K, the value of built-in potential (V _bi) decreases from 1.17 V to 0.98 V. Device shows maximum efficiency when FTO is used as the front electrode, and Au is used as a back electrode. The optimum device, made of FTO/ZnO/Cs₂AgBiBr₆/NiO/Au, provides V _oc = 1.29 V, J _sc = 20.69 mA cm⁻², fill factor = 81.72%, and PCE = 21.88%.

An ideal n-i-p perovskite solar cell employing a Pb free CH₃NH₃SnI₃ absorber layer was suggested and modelled. A comparative study for different electron transport materials has been performed for three devices keeping CuO hole transport material (HTL) constant. SCAPS-1D numerical simulator is used to quantify the effects of amphoteric defect based on CH₃NH₃SnI₃ absorber layer and the interface characteristics of both the electron transport layer (ETL) and hole transport layer (HTL). The study demonstrates that amphoteric defects in the absorber layer impact device performance significantly more than interface defects (IDL). The cell performed best at room temperature. Due to a reduction in V_oc, PCE decreases with temperature. Defect tolerance limit for IL1 is 10¹³ cm⁻³, 10¹⁶ cm⁻³ and 10¹² cm⁻³ for structures 1, 2 and 3 respectively. The defect tolerance limit for IL2 is 10¹⁴ cm⁻³. With the proposed device structure FTO/PCBM/CH₃NH₃SnI₃/CuO shows the maximum efficiency of 25.45% (V_oc = 0.97 V, J_sc = 35.19 mA/cm², FF = 74.38%), for the structure FTO/TiO₂/CH₃NH₃SnI₃/CuO the best PCE is obtained 26.92% (V_oc = 0.99 V, J_sc = 36.81 mA/cm², FF = 73.80%) and device structure of FTO/WO₃/CH₃NH₃SnI₃/CuO gives the maximum efficiency 24.57% (V_oc = 0.90 V, J_sc = 36.73 mA/cm², FF = 74.93%) under optimum conditions. Compared to others, the FTO/TiO₂/CH₃NH₃SnI₃/CuO system provides better performance and better defect tolerance capacity.

This study investigates the potential use of eco-friendly, all-inorganic cesium tin iodide (CsSnI₃) perovskite (PVK) as an absorber layer. Despite having higher temperature stability of CsSnI₃, the challenge is to get a uniform and defect-free film that hinders the performance. To accomplish this goal, we investigated several performance-related variables for perovskite solar cells (PSCs), including material defect density (N_t ), transport materials, layer thickness, temperature impacts, and back contact work functions. Negative valence band or conduction band offset values indicate no barrier preventing photogenerated carriers from flowing into the charge transport layers. The simulation result shows that hole transport layer thickness shows a higher impact than electron transport layer thickness. For the PVK thickness of 500 nm and a carrier density of 10¹⁸ cm⁻³, the device offers an optimum power conversion efficiency of 20.1%. The performance is more significantly affected by the defects in the PVK material compared to the defects present at the interface. Higher recombination (R_e−h+) occurs at the TiO₂–CsSnI₃ interface. Defects located within the deep-level trap positioned at the mid-point of the band gap energy (E _g) have a negative impact on the performance. The temperature coefficient (C _T) is approximately ‒0.367% K^‒1, indicating excellent thermal stability in an open environment. The selection of ‘A’ cation, the addition of additives, or carefully controlled fabrication techniques can mitigate the defect. This research shows the strategy for creating defects-free PSC devices, ultimately enhancing performance and the stability.

Kesterite (CZTSSe) has emerged as a sustainable thin-film absorber, yet its device efficiencies remain below those of leading photovoltaic technologies. Optimizing the buffer layer (BL) is a promising strategy to overcome these limitations. Here, we combined density functional theory (DFT) calculations with SCAPS-1D simulations to systematically evaluate ZnS polymorphs (cubic, hexagonal, trigonal) as a BL for CZTSSe solar cells. DFT analysis (GGA-PBE, CASTEP) reveals band gaps of 3.51 eV (cubic), 3.52 eV (hexagonal), and 3.53 eV (trigonal). The hexagonal phase exhibits superior carrier transport properties with electron and hole mobilities of 343.2 and 92.6 cm² V⁻¹ s⁻¹, respectively. Density-of-states analysis confirms Zn-3d orbitals lie deep in the valence band, with S-3p levels predominating close to the Fermi level, and Zn-4s/4p defining the conduction band, highlighting S-3p → Zn-4s/4p transitions. SCAPS-1D simulations for the device ITO/AZO/ZnS/CZTSSe/Au demonstrate that the crystal phase of ZnS strongly impacts photovoltaic performance. Utilizing hexagonal ZnS BL achieves the highest efficiency (PCE 14.18%, J_SC 25.93 mA cm⁻², FF 62.5%) due to the higher mobility of that crystal system. Furthermore, systematic variation of ZnS thickness, donor density, mobility, band gap, and bulk/interface defect densities, along with back-contact work function and operating temperature, reveals critical design parameters governing charge recombination, series resistance, and interfacial quality to improve performance. This combined theoretical-simulation study highlights that hexagonal ZnS emerges as the most effective BL for CZTSSe solar cells, offering superior carrier transport and interfacial stability for enhanced device efficiency.

A combined DFT and SCAPS-1D simulation reveals SnO ₂ polymorphs greatly impact Cs ₂ TiBr ₄ perovskite solar cells. Tetragonal SnO ₂ produces the highest efficiency (11.6%), underscoring the significance of interfacial engineering and ETL polymorphism.