Browsing by Author "Olyaeefar, Babak"
Now showing 1 - 5 of 5
Results Per Page
Sort Options
Item Embargo Classical modeling of extrinsic degradation in polycrystalline perovskite solar cells defect induced degradation(Elsevier BV * North-Holland, 2023-08-18) Mahiny, M.; Ahmadi-Kandjani, S.; Olyaeefar, BabakIn the realm of photovoltaic devices, the future appears bright for polycrystalline perovskite solar cells. However, the promise of their efficiency is threatened by a myriad of degradation mechanisms. These mechanisms, like dark spots on a sunny day, create shadows of uncertainty on the performance of polycrystalline PSCs. Nonetheless, this article comprehensively explains these degradation mechanisms and their impact on grain boundaries in PSCs. The paper investigates grain boundaries’ effects on carrier lifetime by employing various models, such as the Matthiessen rule and the Drude–Smith method. The findings reveal that defect density is the primary factor affecting the material’s performance, and grain boundaries’ size influences its changes. Drude–Smith’s model provides a more precise estimation of the mobility, total scattering lifetime, and PL quantum yield in polycrystalline semiconductors with reduced scattering time. The presented method is verified by feeding extracted parameters into Drift-Diffusion equations and fitting them with reported experimental photovoltaic conversion efficiency data. Furthermore, based on the simulation results and the strong correlation between grain boundaries and the time factor, the study proposes a comprehensive model that can effectively predict PSCs’ degradation time.Item Open Access Performance analyses of highly efficient inverted all-perovskite bilayer solar cell(Nature Publishing Group, 2023-05-22) Gholami-Milani, A.; Ahmadi-Kandjani, S.; Olyaeefar, Babak; Kermani, M. H.Numerical simulation of an all-perovskite bilayer solar cell has been conducted by the SCAPS-1D. The presented structure employs MAPbI3 as a relatively wide bandgap (1.55 eV) top absorber and FA0.5MA0.5Pb0.5Sn0.5I3 as a narrow bandgap (1.25 eV) bottom absorber. The viability of the proposed design is accomplished in two steps. First, to validate this study, two inverted solar cells in standalone conditions are simulated and calibrated to fit previously reported state-of-the-art results. Second, both these devices are appraised for the bilayer configuration to boost their performances. Affecting parameters such as the thickness of perovskite absorbers, the work function of front and rear contacts, and the effect of temperature have been studied because solar cells are temperature-sensitive devices, and also carrier concentration and their mobility get overwhelmingly influenced as temperature increases. It is manifested that using bilayer structures could easily widen the absorption spectrum to the near-infrared region and significantly enhance the performance of the device which is mainly affected by the thickness of the FA0.5MA0.5Pb0.5Sn0.5I3 layer. Also, it has been found that the work function of the front contact has a prominent role with its optimal values being above 5 eV. Finally, the optimized inverted all-perovskite bilayer solar cell delivers a power conversion efficiency of 24.83%, fill factor of 79.4%, open circuit voltage of 0.9 V, and short circuit current density of 34.76 mA/cm2 at 275 K and a thickness of 100 nm and 600 nm for MAPbI3 and FA0.5MA0.5Pb0.5Sn0.5I3, respectively.Item Open Access Quasi PT-symmetric design for single-mode high-power edge-emitting semiconductor lasers(IEEE - Institute of Electrical and Electronics Engineers, 2023-09-04) Olyaeefar, Babak; Şeker, Enes; Şengül, Serdar; Dadashi, Khalil; Teimourpour, M. H.; El-Ganainy, R.; Demir, AbdullahLarge-area lasers are utilized for generating higher optical powers. However, enlarged cross-sections for increased current injection lead to the introduction of high-order modes, decreased beam qualities, and limited applicability. Available mode filtering approaches such as adiabatic amplifiers, tapered designs, laterally inhomogeneous structures, and refractive index modulations mostly adversely affect the fundamental mode and require added steps and complexities in the fabrication. As a novel concept in quantum mechanics, PT-symmetric (PTS) designs have found their only experimental validation in optical devices. They have shown capabilities in high-order mode filtering by inducing selective modal losses on the coupled higher-order mode from a pumped main potential to a lossy partner potential. Again, these systems require precise adjustments to avoid affecting the fundamental mode. Here, we introduce the quasi-PTS concept, with reduced operational sensitivity, to selectively force loss on the high-order mode while keeping the fundamental mode intact. This design is based on adjusting the width of the passive partner to support the higher-order mode of the main potential as its first mode. We present experimental evidence for an electrically pumped, large-area edge-emitting laser with high-power emission above 400mW and high beam qualities below 1.2. Beyond prior proof-of-concept investigations, this study provides the first unambiguous demonstration of PTS applicability in designing laser geometries with industrial output power levels and emission characteristics.Item Open Access Single-mode operation of electrically pumped edge-emitting lasers through cavity coupling of high order modes(SPIE, 2022-03-04) Şeker, Enes; Şengül, Serdar; Dadashi, Khalil; Olyaeefar, Babak; Demir, AbdullahThe output power of a typical single-mode semiconductor laser is limited by its narrow waveguide width required to cut off high-order spatial modes. Conventional techniques rely on engineering the waveguide without introducing higherorder modes. In contrast, this work utilizes the concept of coupled-cavity (CC) structures. A single-mode lasing is achieved by employing a multi-mode and a neighboring single-mode waveguide. The CC approach is based on the resonant coupling of the high-order mode in the wide waveguide to the fundamental mode of a narrower lossy waveguide. First, geometrical dispersion of the CC lasers, such as their width, spacing, and their sensitivity to the resonance, was investigated. After optimizing the design, edge-emitting-lasers were fabricated using high-efficiency GaAs-based structures. Optical mode control and single-mode operation of the design are demonstrated through fundamental optical characterization measurements. The output power curves for the single and CC designs show similar slope efficiencies suggesting the proposed method as a promising approach towards high-power single lateral mode operation of edge-emitting lasers.Item Open Access Single-mode quasi PT-symmetric laser with high power emission(Springer Nature, 2023-06-16) Şeker, Enes; Olyaeefar, Babak; Dadashi, Khalil; Şengül, Serdar; Teimourpour, M. H.; El-Ganainy, R.; Demir, AbdullahLarge-area lasers are practical for generating high output powers. However, this often comes at the expense of lower beam quality due to the introduction of higher-order modes. Here, we experimentally demonstrate a new type of electrically pumped, large-area edge-emitting lasers that exhibit a high power emission (∼0.4 W) and a high-quality beam (M2∼1.25). These favorable operational characteristics are enabled by establishing a quasi PT-symmetry between the second-order mode of a large area two-mode laser cavity and that of a single-mode auxiliary partner cavity, i.e., by implementing a partial isospectrality between the two coupled cavities. This in turn enlarges the effective volume of the higher-order modes. As a result, a selective pump applied via current injection into the main laser cavity can provide a stronger modal gain to the fundamental mode, and thus lead to lasing in the single mode regime after filtering out higher order transverse modes. The reported experimental results confirm this intuitive picture and are in good agreement with both theoretical and numerical analysis. Above all, the employed material platform and fabrication process are compatible with the industrial standards of semiconductor lasers. This work provides the first clear demonstration, beyond previous proof-of-concept studies, of the utility of PT-symmetry in building laser geometries with enhanced performance and, at the same time, useful output power levels and emission characteristics. © 2023, The Author(s).