The development of stand-alone germanium solar cells is essential for application of this type of... more The development of stand-alone germanium solar cells is essential for application of this type of cell in highly efficient mechanically stacked solar cells and in Thermo Photo-Voltaic (TPV) systems. Up to now the highest efficiency reported for this type of cell is 6.4 percent (AM0). Simulations show that in order to obtain high efficiencies it is essential to create a shallow emitter and sufficiently passivate the front and back surfaces. The research presented in this paper makes use of a cheap and easy cell process using a spin-on diffusant source to realise the emitter. Passivation of the front surface is obtained by applying amorphous silicon deposited by PECVD. An innovative process is used to create the contact with the emitter through the passivating layer. As a result a cell efficiency of 6.7 percent (AM1.5) is obtained.
Significant improvements in the fill factor and open circuit voltage of large area (>100 cm2) ... more Significant improvements in the fill factor and open circuit voltage of large area (>100 cm2) n-type mc-Si rear junction cells have been obtained using a stack of pure AI and screen-printed AI paste. The AI-alloyed emitter of the cells was improved by using a thin 1-2 micron ...
N-type interdigitated back contact (IBC) silicon solar cells have been successfully applied indus... more N-type interdigitated back contact (IBC) silicon solar cells have been successfully applied industrially with high-efficiency of 23.4% by Sunpower and are being investigated by several research groups. However, the formation of p+ emitter is still an issue. A traditional method is boron ...
ABSTRACT This paper presents the development of single step processes and their integration into ... more ABSTRACT This paper presents the development of single step processes and their integration into a baseline for the lab scale manufacturing of high efficiency IBC cells. The main processes evaluated include cleaning, oxidation, boron and phosphorous doping. Three different cleaning treatments, combined with the optimization of thermal oxidation, have been studied. Lifetime values up to 8 ms at an injection level of 1.1015 cm-3 have been achieved on 280 μm, n-Si FZ wafers with a base resistivity of 1.9 Ω.cm. Boron diffusion is evaluated starting from a boron-doped SiOx CVD layer and compared to the diffusion from a BBr3 source. Both doping processes enable J0 values as low as 10 fA/cm2 with a thermal silicon oxide passivation. We present the evolution of the integration runs as a result from the introduction of the improved steps. With the latest improvements, IV characteristics progressed from efficiencies ∼20% up to 23.3% (calibrated IV values: 696 mV, 41.6 mA/cm2, FF= 80.4% with an efficiency of 23.3%).
Thin layers of intrinsic and doped amorphous silicon have been used as the emitter in a processin... more Thin layers of intrinsic and doped amorphous silicon have been used as the emitter in a processing scheme to form heterojunction interdigitated back contact (HJ-IBC) solar cells. Such processing involved depositing the emitter across the wafer, and subsequent patterning to define the base and emitter regions. Average cell efficiencies of 14.6% have been achieved (with a best cell efficiency of
Deep Level Transient Spectroscopy (DLTS) has been applied to Metal-Oxide-Semiconductor (MOS) capa... more Deep Level Transient Spectroscopy (DLTS) has been applied to Metal-Oxide-Semiconductor (MOS) capacitors fabricated on crystalline silicon n-and p-type substrates, with a SiO2 or a SiO2/SiNx bi-layer passivation stack, covered by an Al gate. It is shown ...
ABSTRACT Thermoelectric generators worn on a person’s body have demonstrated their capability to ... more ABSTRACT Thermoelectric generators worn on a person’s body have demonstrated their capability to power a variety of wireless sensor nodes that are to improve his/her health or comfort. In this article, the design, fabrication and performance of two prototypes of a battery-free wireless 2-channel electroencephalography (EEG) system are presented. The first system is powered solely by a thermoelectric generator that produces 2-2.5 mW of power and is worn as a headband. The second system resembles a diadem or headphones and uses a hybrid power supply that combines a thermoelectric generator and photovoltaic cells in one device. This portable EEG headset considerably improves the comfort of patients in clinical as well as in non-clinical environments and opens perspectives for a new range of non-clinical applications.
The development of stand-alone germanium solar cells is essential for application of this type of... more The development of stand-alone germanium solar cells is essential for application of this type of cell in highly efficient mechanically stacked solar cells and in Thermo Photo-Voltaic (TPV) systems. Up to now the highest efficiency reported for this type of cell is 6.4 percent (AM0). Simulations show that in order to obtain high efficiencies it is essential to create a shallow emitter and sufficiently passivate the front and back surfaces. The research presented in this paper makes use of a cheap and easy cell process using a spin-on diffusant source to realise the emitter. Passivation of the front surface is obtained by applying amorphous silicon deposited by PECVD. An innovative process is used to create the contact with the emitter through the passivating layer. As a result a cell efficiency of 6.7 percent (AM1.5) is obtained.
Significant improvements in the fill factor and open circuit voltage of large area (>100 cm2) ... more Significant improvements in the fill factor and open circuit voltage of large area (>100 cm2) n-type mc-Si rear junction cells have been obtained using a stack of pure AI and screen-printed AI paste. The AI-alloyed emitter of the cells was improved by using a thin 1-2 micron ...
N-type interdigitated back contact (IBC) silicon solar cells have been successfully applied indus... more N-type interdigitated back contact (IBC) silicon solar cells have been successfully applied industrially with high-efficiency of 23.4% by Sunpower and are being investigated by several research groups. However, the formation of p+ emitter is still an issue. A traditional method is boron ...
ABSTRACT This paper presents the development of single step processes and their integration into ... more ABSTRACT This paper presents the development of single step processes and their integration into a baseline for the lab scale manufacturing of high efficiency IBC cells. The main processes evaluated include cleaning, oxidation, boron and phosphorous doping. Three different cleaning treatments, combined with the optimization of thermal oxidation, have been studied. Lifetime values up to 8 ms at an injection level of 1.1015 cm-3 have been achieved on 280 μm, n-Si FZ wafers with a base resistivity of 1.9 Ω.cm. Boron diffusion is evaluated starting from a boron-doped SiOx CVD layer and compared to the diffusion from a BBr3 source. Both doping processes enable J0 values as low as 10 fA/cm2 with a thermal silicon oxide passivation. We present the evolution of the integration runs as a result from the introduction of the improved steps. With the latest improvements, IV characteristics progressed from efficiencies ∼20% up to 23.3% (calibrated IV values: 696 mV, 41.6 mA/cm2, FF= 80.4% with an efficiency of 23.3%).
Thin layers of intrinsic and doped amorphous silicon have been used as the emitter in a processin... more Thin layers of intrinsic and doped amorphous silicon have been used as the emitter in a processing scheme to form heterojunction interdigitated back contact (HJ-IBC) solar cells. Such processing involved depositing the emitter across the wafer, and subsequent patterning to define the base and emitter regions. Average cell efficiencies of 14.6% have been achieved (with a best cell efficiency of
Deep Level Transient Spectroscopy (DLTS) has been applied to Metal-Oxide-Semiconductor (MOS) capa... more Deep Level Transient Spectroscopy (DLTS) has been applied to Metal-Oxide-Semiconductor (MOS) capacitors fabricated on crystalline silicon n-and p-type substrates, with a SiO2 or a SiO2/SiNx bi-layer passivation stack, covered by an Al gate. It is shown ...
ABSTRACT Thermoelectric generators worn on a person’s body have demonstrated their capability to ... more ABSTRACT Thermoelectric generators worn on a person’s body have demonstrated their capability to power a variety of wireless sensor nodes that are to improve his/her health or comfort. In this article, the design, fabrication and performance of two prototypes of a battery-free wireless 2-channel electroencephalography (EEG) system are presented. The first system is powered solely by a thermoelectric generator that produces 2-2.5 mW of power and is worn as a headband. The second system resembles a diadem or headphones and uses a hybrid power supply that combines a thermoelectric generator and photovoltaic cells in one device. This portable EEG headset considerably improves the comfort of patients in clinical as well as in non-clinical environments and opens perspectives for a new range of non-clinical applications.
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Papers by N. Posthuma