Numerical analysis of carbon-based perovskite tandem solar cells: Pathways towards high efficiency and stability

Multi-junction solar cells exhibit superior power conversion efficiency (PCE) in comparison with their single -junction counterparts. The tunable bandgap, low-cost, elevated short circuit current density (Jsc), and open -circuit voltage (Voc) of perovskite solar cells (PSCs) have led to their widespread adoption as top sub-cells in tandem devices. Stability remains a significant challenge for these cells. To address this issue, carbon perovskite solar cells (CPSCs) have emerged as a potential solution, offering enhanced stability without hole transport layers (HTLs). This study focuses on the simulation of HTL-free CPSCs using an improved electron transport material (ETM) instead of TiO2. The implementation of this enhancement leads to a notable increase in the PCE of the CPSCs, rising from 7.97 % to 14.38 %. Through optimizing the defect concentration and doping density of the perovskite absorber layer, a significant improvement in the PCE is achieved, reaching 16.87 %. A novel configuration incorporating a gradient doping profile in the perovskite layer is introduced, leading to a remarkable enhancement in the PCE, which reaches 22.22 %. Two absorber materials are suggested, CIGS and GeTe, as bottom sub-cells. Three tandem cell configurations, PSC/CIGS, CPSC/CIGS, and CPSC/GeTe, are rigorously explored based on the optimized sub-cells. The PCEs of the proposed configurations are found to be 30.52 %, 22.7 %, and 36.59 %, respectively. Computational analysis reveals that the PSC/CIGS tandem cell exhibits lower stability against temperature variations compared to CPSC/CIGS and CPSC/GeTe. Additionally, the proposed CPSC/GeTe tandem is highly praised as a favorable contender, offering both high efficiency and stability among the various configurations considered in this study.