Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F42: Defects in Solar Cell MaterialsFocus
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Sponsoring Units: DMP Chair: Anderson Janotti, University of Delaware Room: Room 318 |
Tuesday, March 7, 2023 8:00AM - 8:12AM |
F42.00001: Using EDMR to Characterize Deep Level Defects in Novel Solar Cells Elijah A Allridge, Patrick M Lenahan, Fedor V Sharov, Abigail Meyer, Chirag Mule, Paul Stradins We have studied deep level defects in a new solar cell technology which is designed to be affordable and easy to manufacture. Electrically detected magnetic resonance (EDMR) and near-zero-field magnetoresistance (NZFMR) allow for the detection of defects by measuring the change in recombination current as a magnetic field is swept across the device and subject to RF (~500 MHz) for low field and X-band microwaves (9-10 GHz) for high field electromagnetic waves. The devices in this study consisted of polycrystalline silicon grown on passivated n-type Czochralski grown Si wafer with p+ and n+ regions located on the bottom and top of the device, respectively. We studied two types of devices that were manufactured with different open circuit voltages. |
Tuesday, March 7, 2023 8:12AM - 8:24AM |
F42.00002: The role of native defects and their diffusivity in CdTe Intuon Chatratin, Igor Evangelista, Anderson Janotti CdTe is a leading thin-film technology for solar-cell applications. Basic features such as the optimum band gap of 1.5 eV and simple manufacturing process have been driving the research on improving the current record efficiency of 22% for CdTe solar cells toward the theoretical limit of 32%. Low p-type doping and short carrier lifetimes in the CdTe absorber have been suggested as the main limiting factors and attributed to defect compensation and carrier recombination. Understanding the role of point defects and impurities in CdTe is crucial to solving these problems. Despite many years of research, the sources of compensation and the microscopic recombination mechanisms are still unclear. By using hybrid density functional calculations with spin-orbit coupling and large supercells, we investigate the electronic properties, the formation energies, and the diffusivities of the native defects in CdTe. As possible sources of compensation for p-type conductivity, we discuss the structural and electronic properties of Cd interstitial, Te vacancies, and TeCd antisites. The stability of each defect is discussed in terms of both the defect formation energy and the migration barrier. We also address possible mechanisms that lead to non-radiative recombination. |
Tuesday, March 7, 2023 8:24AM - 8:36AM |
F42.00003: Role of deep levels in semi-insulating gallium arsenide pulse-compression photoconductive switches Yicong Dong, Shaloo Rakheja The pulse-compression photoconductive switch (PCPS) is a unique high-frequency optoelectronic device that leverages the transferred electron effect in certain semi-insulating (SI) III-V semiconductors like GaAs to realize applications with bandwidths > 100 GHz.1 However, defects present in SI GaAs can significantly influence the PCPS' operation. In this work, we theoretically show the impact of deep levels on electrical characteristics of a GaAs PCPS in both dark and illuminated mode. Specifically, we study electron dynamics in an illuminated two-dimensional PCPS structure using a commercial transport solver and apply a trap extraction methodology2 to examine the transient response of the device during turn-off. In addition, we implement a custom solver to shed light on the steady-state response of PCPS in dark mode by incorporating avalanche effects. We show that recombination centers are crucial for fast turn-off when optical bias is high. In contrast, electron traps degrade peak output current and available bandwidth of the PCPS. To conclude, it is possible to semi-quantitatively characterize major deep levels and their impact on the PCPS performance without Arrhenius measurements of the device. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F42.00004: Density Functional Theory (DFT) Analysis of the Nitrogen Hyperdoping Ability to Induce Intermediate Band (IB) in Silicon Abdennaceur Karoui, Fozia Sahtout, Branislav Vlahovic DFT has been used to evaluate the effectiveness of N hyperdoping in creating intermediate (IB) in silicon. The exchange and correlation functional MGGA, Pseudo-Dojo pseudopotential, a moderately accurate basis set, and 7x7x7 k-points for sampling the Brillouin zone have been used. Large Si supercell (3x3x3 Si unit cells, 216 atoms) was chosen to reduce defect perturbations. This size matches N concentration in hyperdoped silicon. The symmetry reduced the k-points, for instance, to 172 in the case of the substitutional nitrogen (Ns). We focus on VxNyO complexes (x=0,1 and y=0,1,2) in Si. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F42.00005: Shedding (x-ray) light on As-local structures and defects in CdTe solar cells Srisuda Rojsatien, Niranjana Mohan Kumar, Trumann Walker, Barry Lai, Arun Kumar Mannodi Kanakkithodi, Maria K Chan, Dan Mao, Mariana Bertoni Arsenic (As) is being used as a state-of-the-art p-type dopant for polycrystalline cadmium telluride (CdTe) thin film solar cells as it leads to significant increases in acceptor concentration, greater than 1016 cm−3 compared to 1014 cm−3 of the conventional copper p-type doping. However, among As atoms that were incorporated into the CdTe devices, only ~1 % of As atoms are activated, serving as p-type doping and contributing to acceptor concentration. The reason for the low dopant activation and the structures and defects that account for the remaining percentage of the As atoms present is still unknown. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F42.00006: Stability of the black perovskite CsSnI3: a route to eco-friendly solar cells Lorenzo Monacelli, Nicola Marzari Substituting fossil fuels with renewable sources is one of the main challenges of our society, and perovskite solar cells (PSCs) are among the most promising solutions for energy harvesting. However, the most efficient PSCs contain highly toxic lead. CsSnI3 could be one of the most promising eco-friendly alternatives for high-performance PSCs, thanks to the excellent optoelectronic properties of its black phase, but its deployment into general markets is hampered by the rapid phase changes of samples exposed to air. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F42.00007: Atomic-scale Tuning of Ultrathin Memristors Sierra C Seacat, Ryan Goul, Angelo Marshall, Hartwin Peelaers, Franciso C Robles Hernandez, Judy Z Wu Memristors, with proposed applications for logic gates, non-volatile memory, and neuromorphic computing, typically consist of bilayer dielectric conducting oxides sandwiched between two metal contacts. When a voltage is applied, oxygen vacancies diffuse through the material and form a conducting filament, causing the memristor to switch from a high resistance state (HRS) to a low resistance state (LRS). Increasing the concentration of oxygen vacancies can improve the performance of memristors in critical areas such as switching speed and on/off ratio (HRS/LRS). |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F42.00008: Trap-assisted Auger-Meitner recombination from first principles Fangzhou Zhao, Mark E Turiansky, Chris G Van de Walle Trap-assisted nonradiative recombination is a key mechanism limiting the efficiency of optoelectronic devices such as light emitting diodes. Trap-assisted recombination via multiphonon emission (MPE) has been studied from first principles; its rate was found to become negligibly low in materials with band gaps larger than about 2.5 eV, and it cannot explain the experimentally measured trap-assisted recombination rates in such materials. We propose that trap-assisted Auger-Meitner (TAAM) recombination can account for the experimental observations. We have developed a practical first-principles methodology to calculate the TAAM rate in semiconductors. As a case study, we applied our formalism to a calcium substitutional impurity in InGaN. We found that for band gaps larger than 2.5 eV, the combination of hole capture by MPE and electron capture by TAAM results in recombination rates orders of magnitude larger than the recombination rate governed by MPE alone. Our computational formalism is general and can be applied to any defect or impurity in any semiconducting or insulating material. |
Tuesday, March 7, 2023 9:36AM - 10:12AM |
F42.00009: Stabilizing polar phases in binary metal oxides by hole doping Invited Speaker: Rohan Mishra The recent observation of ferroelectricity in the metastable phases of binary metal oxides, such as HfO2, ZrO2, Hf0.5Zr0.5O2, and Ga2O3, has garnered a lot of attention. These metastable ferroelectric phases are typically stabilized using epitaxial strain, alloying, or defect engineering. Here, we propose hole doping is the key factor in all these methods that is responsible for stabilization of polar phases in binary metal oxides. Using first-principles density-functional-theory calculations, we show that holes in these oxides mainly occupy one of the two oxygen sublattices. This hole localization, which is more pronounced in the polar phase than in the nonpolar phase, lowers the electrostatic energy of the system, and makes the polar phase more stable at sufficiently large concentrations. We demonstrate that this electrostatic mechanism is responsible for stabilization of the ferroelectric phase of HfO2 aliovalently doped with elements that introduce holes to the system, such as La and N. Finally, we show that the spontaneous polarization in HfO2 is robust to hole doping, and a large polarization persists even under a high concentration of holes. |
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