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Today’s Solar Power Generating Technologies
Published in Anco S. Blazev, Solar Technologies for the 21st Century, 2021
Contact resistance losses occur at the interface between the silicon solar cell and the metal contact. To keep top contact losses low, the top n+ doped layer must be as heavily doped as possible. However, a high doping level creates other problems. If a high level of phosphorus is diffused into silicon, the excess phosphorus lies at the surface of the cell, creating a “dead layer,” where lightgenerated carriers have little chance of being collected.
Defects induced by Metal-Semiconductor Contacts Formation
Published in Kazumi Wada, Stella W. Pang, Defects in Optoelectronic Materials, 2021
An ideal ohmic contact can flow current without any voltage drop through it, i.e., zero contact resistance. In optoelectronic devices, realization of low-resistance ohmic contacts is a critical issue for low-voltage as well as high-efficiency operation. If the contact resistance is high, for instance, in laser diodes, an actual applied voltage becomes large due to a voltage loss at the contacts, which might heat up the devices and hence degrade the device performance and reliability. In representative electronic devices with compound semiconductors, such as metal-semiconductor field effect transistor (MESFET) and high electron-mobility transistor (HEMT), source and drain contacts must be ohmic. If their contact resistance is high, a parasitic series resistance decreases the effective transconductance [128].
Crystalline Silicon Photovoltaic Technologies
Published in Anco S. Blazev, Photovoltaics for Commercial and Utilities Power Generation, 2020
Contact resistance losses occur at the interface between the silicon solar cell and the metal contact. To keep top contact losses low, the top N+ layer must be as heavily doped as possible. However, a high doping level creates other problems. If a high level of phosphorus is diffused into silicon, the excess phosphorus lies at the surface of the cell, creating a “dead layer,” where light-generated carriers have little chance of being collected. Many commercial cells have a poor “blue” response due to this “dead layer.” Therefore, the region under the contacts should be heavily doped, while the doping of the emitter is controlled by the trade-offs between achieving a low saturation current in the emitter and maintaining a high emitter diffusion length.
Thermal modelling, performance analysis and exergy study of a concentrated semi-transparent photovoltaic-thermoelectric generator (CSPV-TEG) hybrid power generation system
Published in International Journal of Sustainable Energy, 2021
Abhishek Tiwari, Shruti Aggarwal
Ouyang and Li (2016) studied segmented TEGs through simulation of various TE materials spanning across a wide temperature range from 300 K to 1000 K. The results showed that combination of p type thermoelectric materials, namely BiSbTe, AgPbSbTe, MgAgSb,K-doped PbTeS and SnSe with n type thermoelectric materials, namely Cu doped BiTeSe, AgPbSbTe and SiGe in order to build segmented legs enabled thermoelectric modules to achieve electrical efficiencies up to 17% and 20.9% at the temperature differences of 500 and 700 K, respectively. Also, a high output power density of 2.1 W/cm2 was achieved at the temperature difference of 700 K. The effects of thermal radiation, electrical and thermal contact were also studied. Liang, Zhou, and Huang (2011) carried out a study of an analytical model of a parallel thermoelectric generator. The study included performance analysis of a parallel thermoelectric generator (TEG) by theoretical analysis and experimental test. The theoretical analysis and calculation were based on law of conservation of energy, semi-conductor thermoelectric theory and law of thermodynamics. The mathematical expressions of power output and current of parallel TEG were deduced by the analytical model. The results showed that parallel properties of TEG are the same as that of common DC power when all TE modules in parallel TEG have same inherent parameters and working conditions. The results also depicted that the thermal contact reduces the power output by reducing the temperature difference across the thermocouples and existence of contact resistance increases the thermoelectric module’s internal resistance.
Organic π-type thermoelectric module supported by photolithographic mold: a working hypothesis of sticky thermoelectric materials
Published in Science and Technology of Advanced Materials, 2018
Norifusa Satoh, Masaji Otsuka, Tomoko Ohki, Akihiko Ohi, Yasuaki Sakurai, Yukihiko Yamashita, Takao Mori
Additionally, the σ of ECAs strongly affects the total contact resistance because ECAs have two contacting interfaces with electrodes and with TE legs even though it assists the physical contact between electrodes and TE legs (Figure 10(a)). Contact resistance depends on σ of the two contacting materials; for example, semiconductor devices form high σ heavily doped regions under electrodes to make good electric contacts. When fabricating inorganic TE modules, we can braze electrodes and inorganic TE legs with filler metals to make good electric contact. Since organic materials cannot resist the brazing temperature, we need to use less conductive ECAs than brazed metals. Consequently, we cannot achieve good electric contacts in this scheme for organic π-type TE modules. To move the research of flexible TE modules forward, we also need to consider the other factors. In addition to the above disadvantage on contact resistance, ECAs do not have enough mechanical strength to hold the π-type TE module structure especially when the module is bent as a flexible module. Comparing the thickness of organic active layer ~100 nm in the other organic devices, such as organic light diodes and organic solar cells [20,21], we can expect that the TE leg thickness over 20 µm causes huge mechanical stress on the joints (Figure 10(b)). Furthermore, ECAs are generally expensive though this non-vacuum process should be economic. From a viewpoint to utilize the economic process, herein, we state a working hypothesis: low-κ TE materials like organics additionally acquire adhesive and transformable features; namely, sticky TE materials, in order that we can overcome the obstacles above on the flexible π-type TE modules. The low-κ feature is necessary for flexible sheet-type TE modules to maintain the ΔT. Sticky TE materials are favored as pressure-sensitive adhesives because they can adhere to electrodes after simple pressing [22]. By adhering to the electrodes and absorbing the mechanical stress, sticky TE materials enable a simple three-step fabrication process of reliable flexible TE sheets without expensive ECAs (Figure 10(c), (d)).