Search

In this article, different in situ grown plasma‐enhanced chemical vapor deposition (PECVD)‐grown interfacial oxides for n‐type polysilicon‐passivating contacts are investigated. Herein, SiOx(Ny)/n‐type amorphous silicon stacks created from either N2O plasma or O2 plasma are applied to POLy‐silicon on Oxide interdigitated back‐contact (POLO IBC) solar cells using the structured deposition process through a glass mask to create the IBC layout. The impact of plasma exposure time for interfacial oxide growth on solar cell efficiencies is experimentally determined. In the POLO IBC cell results, it is shown that the PECVD oxides SiOxNy and SiOx with optimized plasma exposure time give similar maximum efficiencies of 23.8% and 23.7%, respectively. In these data, the feasibility to deposit a high‐quality in situ PECVD interfacial SiOx(Ny) layers for surface passivation and current transport of passivated contacts at the same time is demonstrated. For the SiOx/n‐type polysilicon stack, it is found that both plasma exposure time for interfacial oxide growth and polysilicon anneal temperature variations can lead to similar optimum of solar cell efficiencies. The current open‐circuit voltage losses due to metallization for the solar cells are analyzed and a realistic efficiency of 25.22% is calculated to achieve optimized POLO IBC solar cells applying the synergistic efficiency gain analysis on Quokka3 simulations. [ABSTRACT FROM AUTHOR]

Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities − a POLO2-IBC cell − has to electrically isolate the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH's 26.1%-efficient POLO2-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p+-(i)-n+ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p+-(i)-n+ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO2-IBC cell. We attribute this to the formation of a conductive channel between the p+ and n+ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack.

Polysilicon-on-oxide (POLO) passivating contacts and interdigitated back-contact (IBC) cell technologies have recently attracted a lot of interest as candidates for the implementation in the next generation of solar cells. An IBC cell with POLO junctions for both polarities − a POLO2-IBC cell − has to electrically isolate the highly defective p+ and n+ poly-Si regions on the rear side of the cell to avoid parasitic recombination. Inserting an initially undoped, intrinsic (i) region between the p+ and n+ poly-Si regions was demonstrated to successfully prevent the parasitic recombination in the transition region of ISFH's 26.1%-efficient POLO2-IBC cell. In order to further improve the conversion efficiency towards 27%, we apply hydrogen-donating dielectric layer stacks to the p+-(i)-n+ POLO interdigitating rear side to enhance the passivation quality of the POLO junctions. We indeed show a significant improvement of POLO junctions on symmetrical full-area homogenously doped reference samples, but when we apply a hydrogen-donating layer stack on the p+-(i)-n+ POLO interdigitating rear side, we observe a strong degradation in the performance of the POLO2-IBC cell. We attribute this to the formation of a conductive channel between the p+ and n+ poly-Si regions due to the strong negative charge density of the hydrogen-donating layer stack. [ABSTRACT FROM AUTHOR]

We introduce a rear-emitter inversion layer (IL) solar cell on n-type crystalline silicon (n-Si). The hole IL is induced by the high density of negative fixed charges in an aluminum oxide (Al2O3) surface passivation layer. For the formation of contacts to the inversion layer, we employ a single-step p+ laser doping process, using aluminum from the Al2O3 layer as dopant source. Lateral hole transport through the IL underneath the n-Si/Al2O3 interface is analyzed by electrical measurements. The IL hole mobility is shown to be only marginally reduced by scattering at the high density of fixed charges at the n-Si/Al2O3 interface, resulting in an inversion layer sheet resistance of 15-18 kΩ/sq (in the dark). The effective sheet resistance of the IL is shown to decrease to below 4 kΩ/sq under solar cell operating conditions. Based on two-dimensional device simulations, we show that the proposed type of n-type silicon IL solar cell has a very high efficiency potential exceeding 26% including contact recombination losses. [ABSTRACT FROM AUTHOR]

This article reports the recent progress of p‐type back junction solar cells featuring an aluminum front grid and an n+‐type passivating polysilicon on oxide (POLO) contact at the cell rear side. The best cell has an efficiency of 22.6% and an open‐circuit voltage of 716 mV, independently confirmed by Institute for Solar Energy Research Hamelin (ISFH) CalTeC. The cell area is 244.5 cm2. The increase in the SiNx capping layer thickness at the cell rear side reduces the deterioration of passivation quality of the POLO contact by screen‐printed silver. This increases the open‐circuit voltage by 22 mV compared with cells with a thinner nitride layer thickness. The investigation with scanning electron microscopy shows that the damage of the POLO contacts underneath the screen‐printed metal contacts is avoided by increasing the SiNx capping layer thickness. A contact resistivity of 2 mΩ cm2 is measured using the transfer length method. [ABSTRACT FROM AUTHOR]

The fabrication of a silicon solar cell on 6 in. pseudo‐square p‐type Czochralski grown silicon wafers featuring poly‐Si‐based passivating contacts for electrons at the cell rear side and screen‐printed aluminum fingers at the front side is demonstrated. The undiffused front surface is passivated with an Al2O3/SiNx stack, and the rear surface is covered with a thin oxide/n+‐poly‐Si/Al2O3/SiNx layer system, contacted by screen‐printed silver fingers. A loss analysis shows that the recombination losses at the metal contacts on both cell sides dominate the total energy losses. A voltage of 700 mV as the highest open‐circuit voltage from a batch of seven cells is achieved, and the best cell efficiency is 22.3%, independently confirmed. [ABSTRACT FROM AUTHOR]

We investigate the passivation quality of hole-collecting junctions consisting of thermally or wet-chemically grown interfacial oxides, sandwiched between a monocrystalline-Si substrate and a p-type polycrystalline-silicon (Si) layer. The three different approaches for polycrystalline-Si preparation are compared: the plasma-enhanced chemical vapor deposition (PECVD) of in situ p+-type boron-doped amorphous Si layers, the low pressure chemical vapor deposition (LPCVD) of in situ p+-type B-doped polycrystalline Si layers, and the LPCVD of intrinsic amorphous Si, subsequently ion-implanted with boron. We observe the lowest J0e values of 3.8 fA cm−2 on thermally grown interfacial oxide on planar surfaces for the case of intrinsic amorphous Si deposited by LPCVD and subsequently implanted with boron. Also, we obtain a similar high passivation of p+-type poly-Si junctions on wet-chemically grown oxides as well as for all the investigated polycrystalline-Si deposition approaches. Conversely, on alkaline-textured surfaces, J0e is at least 4 times higher compared to planar surfaces. This finding holds for all the junction preparation methods investigated. We show that the higher J0e on textured surfaces can be attributed to a poorer passivation of the p+ poly/c-Si stacks on (111) when compared to (100) surfaces. [ABSTRACT FROM AUTHOR]

We show that one-pulse laser-ablation of Al2O3/SiN x layer stacks from silicon wafers can produce substantial p+-type Al-doped regions in the substrate. We present doping profile measurements which show that the Al-doping profiles of the laser-treated region strongly depend on the laser ablation parameters and thickness of the Al2O3 layer. We find for non-passivated laser Al-doping profiles with sheet resistance Rsheet = 180 Ω □−1 a saturation current densities J0,surf = 4 pA cm−2, which is approximately the same recombination activity as that of a boron furnace diffused layer of the same sheet resistance. [ABSTRACT FROM AUTHOR]

The surface passivation properties of thermal-SiO2/plasma-enhanced chemical vapor deposition SiN stacks on 2.5 Ω cm n-type Czochralski silicon substrates have been investigated. By annealing these stacks in air we achieve surface recombination velocities (SRV) lower than 2.4 cm/s for thin SiO2 layers. We find a clear correlation between the thickness of the oxide layers and the annealing duration. We also show that the absolute passivation quality of the SiO2/SiN stacks correlates to the SiO2 thickness. We find that the SRV increases with increasing oxide thickness. We also present data of the surface passivation of these SiO2/SiN stacks after storage in the dark for several weeks. [ABSTRACT FROM AUTHOR]