arXiv subjects

A. Datas

Publications and source records attributed to A. Datas.

3 recordsLinked to original sources

arXiv2026

Germanium Thermophotovoltaic Devices Achieving 7.3% Efficiency Under High-Temperature Emission by Empirical Calorimetry

We report the first empirical efficiency measurement of germanium-based thermophotovoltaic devices under high-temperature, high-irradiance conditions using a high view-factor calorimetric setup. Two TPV cell architectures were fabricated on p-type, highly doped (10^17 cm-3) Ge substrates, differing only in rear contact configuration. A standard device with a gold rear contact achieves a peak efficiency of 7.3 % and a power density of 1.77 W/cm2 at an emitter temperature of 1480 C, while a PERC-type device reaches 6.3 % efficiency and 1.22 W/cm2 at 1426 C. The superior performance of the standard device is attributed to lower series resistance, whereas the PERC design exhibits slightly higher efficiency at lower emitter temperatures (4.0 % vs. 3.8 % at 1150 C) due to enhanced rear-surface reflectivity. A detailed TPV model has been developed and validated across both device architectures. The model identifies out-of-band optical losses as the dominant efficiency-limiting mechanism, primarily caused by strong free-carrier absorption in the highly doped Ge substrate. Using this model, we predict device performance under idealized spectral conditions commonly assumed in prior literature. For a simulated AlN/W spectrally selective emitter, efficiencies as high as 22.3 % at 1800 C are obtained, consistent with previous semi-empirical predictions. In contrast, when previously reported Ge devices are modeled under the realistic graphite emitter spectrum used here, projected efficiencies decrease to as low as 8.1 % at 1480 C. These results show that earlier projections remain valid but idealized and underscore the importance of emitter spectral engineering and substrate optimization. Finally, we present the first direct comparison of Ge and InGaAs TPV devices under identical conditions, demonstrating the superior performance of InGaAs while confirming the cost-driven competitiveness of Ge.

physics.app-ph↗

arXiv2022

Bifacial thermophotovoltaic energy conversion

Thermophotovoltaic (TPV) energy conversion efficiency has recently surpassed 30%. The key behind such high efficiency is the inclusion of a highly efficient mirror in the rear of the TPV cell that turns back to the thermal emitter the outband energy photons. Efficiencies over 50% could be theoretically attainable by approaching a mirror reflectance of 100%. However, the very few percent of outband absorption significantly deteriorate the conversion efficiency. Thus, current research focuses on developing advance mirror designs able to reach an extreme high outband reflectance over 95%. In this article I propose a bifacial TPV cell that enables very efficient photon recycling without using mirrors and that is less sensitive to outband optical losses. The key to this design is that the cell is introduced in a thermal emitter enclosure where it is irradiated from both sides. Then, outband photons transmit through the cell and are re-absorbed in the emitter. Therefore, the optical losses linked to the mirror/cell interface are eliminated, potentially enabling higher photon recycling efficiencies. This article presents a detailed balance simulation of an edge-cooled bifacial TPV cell to demonstrate that bifacial configuration enables higher conversion efficiencies and twice much as power density than monofacial designs, the latter being a remarkable advantage for moderate temperature and low-cost TPV power generation. Therefore, bifacial TPV cells are appealing for developing practical high-efficient and low-cost TPV devices for power generation in an extended range of heat source temperatures.

physics.app-ph↗

arXiv2020

Application of quasi-steady state photoconductance technique to lifetime measurements on c-Ge substrates

Similar to other high quality crystalline absorbers, an accurate knowledge of surface passivation of crystalline Germanium (c-Ge) substrates is crucial for a straightforward improvement of photovoltaic device performance. For crystalline silicon devices, this information is typically obtained by quasisteady state photoconductance (QSS-PC) technique using Sinton WCT-120 tool. In this work, we explore the conditions to adapt this measurement technique to c-Ge substrates. Based on PC-1D simulations, we deduce that a minimum effective lifetime is needed corresponding to an effective diffusion length equal to the substrate thickness. Apart from this, an accurate estimation of the total photogeneration inside the c-Ge sample is also mandatory. This condition implies that the light intensity that impinges onto the sample must be measured with a c-Ge sensor, although the integrated c-Si sensor can be used for high flash intensities. Additionally, the optical factor used to evaluate sample reflectance must be also known, which is determined by measuring robust effective lifetime values under photoconductance decay conditions. Finally, knowledge about carrier mobility in c-Ge is also necessary to translate the measured photoconductance to the corresponding excess carrier density values. Lifetime measurements of passivated c-Ge substrates done by QSS-PC technique are validated by comparing them with the ones obtained by microwave photoconductance technique.

physics.app-ph↗