Device engineering of lead‐free FaCsSnI3/Cs2AgBiI6‐based dual‐absorber perovskite solar cell architecture for powering next‐generation wireless networks
Authors: Baruah Smriti , Borah Janmoni , Reddy Perugu Yaswanth , Sindhupriya Chamarthi , Sathvika Nara , Rajasekaran Subramaniam 
Published: July 2024

Solar‐powered devices, such as wireless networks, are a crucial component of the Internet of Things (IoT). Designing and creating a solar cell architecture with an extended light absorption regime at a reasonable cost is therefore exceedingly important. All inorganic bismuth‐based Cs2AgBiI6 planar perovskite solar cells (PSCs) have garnered enormous significance due to their exceptional stability against oxygen, heat, and moisture. However, the power conversion efficiencies of Cs2AgBiI6‐based planar PSCs remain relatively low, primarily due to their limited light absorption range and interfacial charge recombination losses. This issue can be effectively addressed using a novel multi‐absorber architecture that incorporates dual absorbers with both lower band gap and wider band gap materials. This approach extends the light absorption range, enabling maximal utilization of the solar spectrum. Therefore, this article incorporates numerical modeling and guided optimization of ITO/ETL/Cs2AgBiI6/Fa0.75Cs0.25SnI3/HTL/Ag dual absorber‐based heterojunction structure to improvise the power conversion efficiency of Cs2AgBiI6‐based single‐absorber PSCs. The proposed configuration employs dual perovskite absorber layers (PALs) consisting of wide band gap Cs2AgBiI6 (1.6 eV) as the top absorber layer along with narrow bandgap Fa0.75Cs0.25SnI3 (1.27 eV) to act as the bottom absorber layer. Before evaluating the bilayer configuration, two standalone PSC architectures, namely, ITO/ETL/Fa0.75Cs0.25SnI3/HTL/Ag (D1)‐ and ITO/ETL/Cs2AgBiI6/HTL/Ag (D2)‐based PSC have been simulated and computed to perfectly fit the earlier anticipated state of art results. After effective validation of the photovoltaic parameters of the standalone architectures, both the absorber layers are appraised to constitute a dual active layer configuration ITO/ETL/Cs2AgBiI6/Fa0.75Cs0.25SnI3/HTL/Ag (D3) maintaining the overall absorber layer width constant to elevate the overall solar cell efficiency. Herein, a combination of various competent hole transport layers (HTLs) such as CBTS, CFTS, Cu2O, CuI, CuO, CuSCN, P3HT, PEDOT:PSS, and Spiro‐OMeTAD, as well as electron transport layers (ETLs) like C60, CeO2, IgZo, PCBM, TiO2, WS2, and ZnO, are adopted and compared to attain highly efficient bilayer PSC configuration. The crucial variables of all ETL‐ and HTL‐based proposed bilayer solar cell configurations including the thickness of PALs, the width of the carrier transport layers, defect densities of transport layers, the effect of operating temperature, series, and shunt resistances have been extensively optimized and tuned to attain preeminent photovoltaic power conversion efficiencies (PCEs) and quantum efficiencies (QEs). It has been well evinced that the proposed configuration with dual‐absorber layers could effectively widen the light absorption regime to the near‐infrared range and thus significantly contribute toward enhanced photovoltaic performance. The simulation results attained with SCAPS showcase the outstanding performance of the proposed dual active layer solar structure obtained with the combination of CuSCN HTL and TiO2 ETL pair. The work concludes a 35.01% optimized efficient ITO/TiO2/Cs2AgBiI6(PAL‐2)/Fa0.75Cs0.25SnI3(PAL‐1)/CuSCN/Ag bilayer solar cell configuration with enhanced short circuit current density (Jsc) of 32.24 mA/cm2, open circuit voltage (Voc) of 1.273 V, and 85.31% fill factor (FF) with 0.6‐ and 0.8‐μm PAL‐1 and PAL‐2 width respectively and 1014‐cm−3 defect density under AM1.G solar spectrum illumination with 1000‐W/m2 light power density. The proposed eco‐friendly solar structure will also help in providing power backup to the next‐generation communication units and devices. Notably the dual‐absorber structure integrating Cs2AgBiI6 and Fa0.75Cs0.25SnI3 materials demonstrates significant advantages in quantum efficiency and spectral coverage compared to using either material independently as single absorbers. The proposed model achieves a peak efficiency of approximately 93% across a spectral range of 300–975 nm, surpassing the 90% efficiency obtained with a single Cs2AgBiI6 absorber covering 300–700 nm. Moreover, it exceeds the 89% efficiency achieved by the single Fa0.75Cs0.25SnI3 absorber within the 300‐ to 974.5‐nm spectral range. Solar cells play a pivotal role in ensuring the sustainability, reliability, and cost efficiency of powering wireless nodes, especially in remote or environmentally sensitive areas where traditional power sources may be inadequate or unavailable. The proposed PSC, with a PCE of 35.01%, can generate 350.1 watts under standard test conditions. This provides sufficient power to support approximately 70 wireless nodes, including wireless sensor nodes, IoT devices, and others, each consuming approximately 5 watts of power.