الفهرس 
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Abstract
The primary purpose of recent research on solar cells is to achieve a higher power conversion efficiency (PCE) with stable characteristics. Multi-junction solar cells have higher PCEs than single-junction cells. Perovskite solar cells (PSCs) are rapidly used as a top sub-cell due to their tunable bandgap, low-cost, high short-circuit current density and open-circuit voltage. One of the main challenges in these cells is the stability issue. Carbon perovskite solar cells (CPSCs) without a hole transport layer (HTL) presented a promising solution for PSCs’ stability. The two-terminal monolithic tandem solar cells demonstrate the commercial tandem cells market. Consequently, all the proposed tandem cells are equivalent to two-terminal monolithic tandem devices. In this work, firstly, a PSC as a top sub-cell with the traditional structure and copper indium gallium selenide (CIGS) solar cell as a bottom sub-cell are used to propose a PSC/CIGS tandem solar cell with a moderate PCE of 30.5% and stability. Secondly, various CPSCs without HTL have been simulated to replace titanium dioxide (TiO2) with a more efficient ETM. Further, the defect concentration and doping of the perovskite absorber layer are optimized, resulting in increasing the PCE. Moreover, a new configuration with gradient doping in the perovskite material is proposed, causing a substantial increase in the PCE, which reaches 22.22%. An efficient perovskite solar cell (PSC) with Spiro-OMeTAD as a hole transport material (HTM) and with no electron transport material (ETM) to replace the traditional PSC structure is presented with a PCE of 27.74%. Replacing the Spiro-OMeTAD with Cu2O and optimizing this material yields to PCE of 33.45%. The results show that an n-p heterojunction PSC structure with an ETM free could be a good candidate for the traditional n-i-p structure. Two absorber materials, CIGS and GeTe, are suggested and optimized as bottom sub-cells. The CIGS cell after optimization has a PCE of 22.13%. The proposed GeTe cell has a superior short circuit current density (Jsc) of 53.3 mA/cm2 and PCE of 26.21%. The optimization of the thickness of the top sub-cells is accomplished by utilizing a numerical algorithm. Based on the optimized top and bottom sub-cells, four tandem cell configurations are thoroughly investigated, besides the PSC/CIGS cell. The PCEs of the proposed CPSC/CIGS, and CPSC/GeTe tandem cells are found to be 22.7%, and 36.59%, respectively. It is computationally revealed that the PSC/CIGS tandem cell has lower stability against temperature variation than CPSC/CIGS and CPSC/GeTe. In addition, the proposed CPSC/GeTe tandem cell is recommended, as a promising candidate, which offers a highly efficient and stable cell amongst the various presented cells. An ETL-free PSC/GeTe tandem cell is proposed for the first time to provide an efficient tandem solar cell with a PCE of 45.99%. Because of such investigations, a proposed four-terminal (4T) ETL-free PSC/CIGS cell could be a milestone in 4T tandem cells with a PCE as high as 35.8%. Finally, a comparison between the performance metrics of the proposed tandem solar cell and those of other recent studies is provided. All the simulations performed in this study, are accomplished by using SCAPS-1D.
This thesis is organized as follows:
Chapter 1: introduces the motivation, problem statement, and the main contributions of this work.
Chapter 2: illustrates the solar cell fundamentals and the state of the art of tandem solar cells.
Chapter 3: proposes the main structure of the suggested tandem solar cells, the working mechanism of SCAPS-1D, and the parameters of the used materials.
Chapter 4: proposes the designing of top and bottom sub-cells.
Chapter 5: discusses the achieved results.
Chapter 6: concludes the work in this thesis and proposes the recommended future work.
Keywords:
Carbon perovskite solar cell (CPSC); Copper Indium Gallium Sulfide (CIGS); Efficient Tandem Solar Cell; ETL-Free PSC; Germanium Telluride (GeTe); Optimized tandem cell; SCAPS-1D; Zinc Oxide (ZnO); Zinc Selenide (ZnSe).