P-type Crystalline Silicon Solar Cells Research Articles

Interfacial energy-band engineering for high open-circuit voltage of rear emitter p-type crystalline silicon solar cells

Rear emitter p-type crystalline silicon (c-Si) tunnel oxide passivating contact (P-TOPCon) devices with low-resistivity (≤1 Ω.cm) c-Si wafer and high-conductivity phosphorus doped (n-type) polysilicon passivating contact (n-poly-Si PC) are expected to achieve high built-in potential (Vbi) and thus open-circuit voltage (Voc). However, the results indicate that the high conductivity of n-poly-Si PC considerably deteriorates the interface passivation quality and lowers the device's Voc. A crucial factor to consider is that the hole and electron can tunnel and recombine together at the c-Si/n-poly-Si PC contact, resulting in a decrease in the quality of interfacial passivation. To inhibit carrier tunnel diffusion and enable energy band engineering at the interface for achieving high Voc, a thin intrinsic poly-Si buffer layer (10 nm) is inserted between SiO2 and n-poly-Si PC. When compared to a device without a buffer, a device with the buffer exhibits a significant improvement in passivation quality and hence Voc. The device with buffer has a Voc of 705 mV and an efficiency of 23.5 %, while that without buffer is 681 mV and 22.6 %, respectively. The introduced buffer has little effect on the industrial manufacturing process, but it does significantly enhance Voc. It has the potential to improve the efficiency of the P-TOPCon devices.

Solution-processed copper(i) iodide via co-doping for enhanced hole selective contacts in p-type crystalline silicon solar cells

We have demonstrated that solution-processed CuI films via Al3+ and I2 co-doping act as effective full-area hole-selective contact layers, generating a remarkable power conversion efficiency of 18.28% for Al3+–I2:CuI/p-Si heterojunction solar cells.

Elucidating the mechanism of potential induced degradation delay effect by ultraviolet light irradiation for p-type crystalline silicon solar cells

A mechanism of potential induced degradation (PID) delay effect by ultraviolet (UV) light irradiation during PID test for p-type crystalline silicon (c-Si) solar cells was proposed in this work. The degradation rate of the solar cell performances is slowed down by the UV light irradiation in the 300–390 nm wavelength range during PID test. The conductivity increase of the silicon nitride (SiNx) anti-reflection coating (ARC) layer on the solar cell surface under UV light irradiation during PID tests, which relates to the mechanism preventing the penetration of sodium ions into the active cell layer, induces the PID delay effect for the p-type c-Si solar cells. The PID delay effect was also analyzed by a microwave photo-conductance decay (μ-PCD) technique in this work. The reduction behavior of the components in the μ-PCD signal curves including rapid (τ1) and slow (τ2) decay time constants and the effective lifetime (τeff) presents a good correlation with the performance degradation behavior of the solar cells over PID test duration. Moreover, the reduction rate of these components is also slowed down under the UV light irradiation in the 300–390 nm wavelength range during PID tests. Notably, their reduction behavior was compatible with the mechanism of the conductivity increase of the SiNx ARC layer under UV light irradiation.

The influence of sodium ions decorated micro-cracks on the evolution of potential induced degradation in p-type crystalline silicon solar cells

In recent years, potential induced degradation (PID) has been a topic of interest to scientists because of its significant impact on performance deterioration of solar cells. Research has shown that the major cause of PID defects for p-type Si solar cells is sodium (Na) ion migration from the soda-lime glass through the encapsulation layer into the solar cell. However, limited scientific investigations have been done on the influence and mechanism of Na ion decorated micro-cracks on the evolution of PID. In this work, Na ion decoration in micro-cracks as the important mechanism causing PID in p-type crystalline Si solar cells is presented and discussed in detail. Furthermore, a model of PID mechanism due to micro-cracks is proposed.

23% efficient p-type crystalline silicon solar cells with hole-selective passivating contacts based on physical vapor deposition of doped silicon films

Of all the materials available to create carrier-selective passivating contacts for silicon solar cells, those based on thin films of doped silicon have permitted to achieve the highest levels of performance. The commonly used chemical vapour deposition methods use pyrophoric or toxic gases like silane, phosphine and diborane. In this letter, we propose a safer and simpler approach based on physical vapour deposition (PVD) of both the silicon and the dopant. An in-situ doped polycrystalline silicon film is formed, upon annealing, onto an ultrathin SiOx interlayer, thus providing selective conduction and surface passivation simultaneously. These properties are demonstrated here for the case of hole-selective passivating contacts, which present recombination current densities lower than 20 fA/cm2 and contact resistivities below 50 mΩ cm2. To further demonstrate the PVD approach, these contacts have been implemented in complete p-type silicon solar cells, together with a front phosphorus diffusion, achieving an open-circuit voltage of 701 mV and a conversion efficiency of 23.0%. These results show that PVD by sputtering is an attractive and reliable technology for fabricating high performance silicon solar cells.

Microscale Spatially Resolved Characterization of Highly Doped Regions in Laser-Fired Contacts for High-Efficiency Crystalline Si Solar Cells

Laser-fired contact (LFC) processes have emerged as a promising approach to create rear local electric contacts in p-type crystalline silicon solar cells. Although this approach has been successfully applied in devices showing efficiencies above 20%, there is still a lack of knowledge about some specific features of LFCs at the submicron level. In this study, we used micro-Raman and microphotoluminescence (PL) spectroscopies to carry out a highresolution spatially resolved characterization of LFCs processed in Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -passivated c-Si wafers. Relevant information concerning features such as local doping distribution and crystalline fraction of the laser-processed region has been obtained. In particular, interesting qualitative and quantitative variations concerning the doping profile have been observed between LFCs processed at different laser powers. Finally, conductive-atomic force microscopy measurements have allowed to identify the existence of highly conductive zones inside the LFCs greatly correlated with highly doped regions revealed by Raman and PL data. This study gives a detailed insight about the LFCs characteristics at the submicron level and their possible influence on the performance of final devices.

Feasibility of Antireflection and Passivation Coatings by Atmospheric Pressure PECVD

An innovative method to obtain antireflection and passivation coatings on p-type crystalline silicon solar cells is presented. The method consists in the growth of hydrogenated silicon nitride films (SiNx:H) by atmospheric pressure plasma enhanced chemical vapor deposition (AP-PECVD). Compared to industrial process, using this kind of processing may allow an augmentation of the silicon solar cell production throughput and yield enabling a reduction of the cost of photovoltaic systems. The optical and passivation properties of the SiNx:H films grown by AP-PECVD are determined and compared with the standard low pressure plasma enhanced chemical vapor deposition (LP- PECVD) films. Minority carrier lifetime of 1ms was reached. Solar cells coated with AP-PECVD SiNx:H films were made, and their performances were compared with standard SiNx:H coated cells. The same cell efficiency is obtained for the two groups of cells proving the interest of the AP-PECVD for the solar cell industry.

前瞻晶体硅太阳能电池未来产业化&amp;mdash;&amp;mdash;高效N型背结前接触和背结背接触晶体硅太阳能电池

In this article, high energy-conversion-efficiency N-type back-junction front-contact and back-junction back-contact mono-crystalline silicon solar cells are explored and reviewed in terms of their research and mass-production prospects. The basic physical mechanism of such two types of high-efficiency N-type solar cells is elaborated. Moreover, the current research on N-type IBC solar cells with screen-printed Aluminum belt-firing p+-type emitter is critically addressed. It is considered to be one of the most promising candidates for the evolution of the commercialized P-type crystalline-silicon solar cells.

Large-Area Crystalline Silicon Solar Cell Using Novel Antireflective Nanoabsorber Texturing Surface by Multihollow Cathode Plasma System and Spin-On Doping

We present 11.7% efficient p-type crystalline silicon solar cells with a nanoscale textured surface and no dielectric antireflection coating. We propose nanocrystalline-like textured surface consisting of nanocrystalline columnar structures of diameters from 50 to 100 nm and depth of about 500 nm formed by reactive-ion etching (RIE) in multihollow cathode system. This novel nano textured surface acts as an antireflective absorbing surface of c-Si abbreviate as ARNAB (antireflective nanoabsorber). Light shining on the surface of RIE-etched silicon bounces back and forth between the spikes in such a way that most of it never comes back. Radio frequency (RF) hollow cathode discharge allows an improvement of plasma density by an order of magnitude in comparison to standard RF parallel-plate discharge. Desirable black silicon layer has been achieved when RF power of about 20 Watt per one hollow cathode glow is applied for our multihollow cathode system. The RF power frequency was 13.56 MHz. The antireflection property of ARNAB textured surface has been investigated and compared with wet-textured and PECVD coated silicon samples. Solar cell using low-cost spin-on coating technique has been demonstrated in this paper. We have successfully achieved 11.7% efficient large area (98 cm2) ARNAB textured crystalline silicon solar cell using low-cost spin-on coating (SOD) doping.

Performance improvement of p-type silicon solar cells with thin silicon films deposited by low pressure chemical vapor deposition method

It is known that surface passivation plays a significant role in upgrading solar cell performance. In this study, silicon thin films deposited by LPCVD (low pressure chemical vapor deposition) are used to passivate the surface of solar-grade p-type crystalline silicon solar cells for the first time. Intrinsic amorphous silicon films and poly-silicon films were obtained on the front and rear surfaces of solar wafers at the deposition temperatures of 560°C and 620°C, respectively. Both kinds of silicon films proved to be effective in improving the open-circuit voltage owing to surface passivation for crystalline silicon solar cells. Optical spectral responses in the short and long wavelength ranges (e.g. the range 300–600nm and the range 850–1100nm, respectively) also showed an improvement in photogenerated current resulting from reduced surface recombination rates on the front and back surface.

Influence of the compensation level on the performance of p-type crystalline silicon solar cells: Theoretical calculations and experimental study

We have investigated the influence of the compensation level on the performance of p-type crystalline silicon solar cells by combining theoretical calculations and experiments. With the compensation level increasing, the fraction of ionized boron (B) atoms increases. The hole mobility is significantly reduced due to the increased ionized impurities scattering, while the electron mobility almost keeps constant due to the inverse contributions of ionized impurities scattering and electron–hole scattering. The carrier lifetime in compensated silicon, mainly dominated by high concentration of dopants, could get improved. Correspondingly, the minority carrier diffusion length increases, causing a higher short-circuit current. However, the open-circuit voltage first decreases and then increases with the increase of the compensation level, owing to the competition effect of the reduced net doping concentration and the increased excess carrier concentration. All these factors could finally result in a higher efficiency solar cell. These results suggest that intentional dopant compensation might be utilized for the improvement of solar cell efficiency, which is especially interesting for those based on highly-doped silicon feedstock.

Self-aligned local contacts through a-Si:H passivation layer

A novel method forms less than 100μm wide self-aligned local contacts through an amorphous silicon based passivation layer stack on crystalline silicon solar cells. Wire shading during the plasma deposition of the passivation layer enables local contact formation without the use of photolithography or laser processes. Subsequent full area aluminum evaporation and thermal annealing create good electrical contacts. The structure combines a low effective surface recombination velocity 36cm/s and high implied open circuit voltage 715mV with a good ohmic contact for the rear side of p-type crystalline silicon solar cells.

Influence of substitutional metallic impurities on the performances of p-type crystalline silicon solar cells: The case of gold

The influence of a gold bulk contamination on the performances of boron doped p-type crystalline silicon solar cells is investigated for different base doping levels and different kinds of materials, such as float zone Si, Czochralski Si, and multicrystalline Si. Solar cells are made from intentionally contaminated silicon wafers. By monitoring the evolution of the electrically active substitutional gold concentration by means of bulk lifetime and minority carrier diffusion length measurements, this paper highlights the eventual gettering or hydrogenation effects occurring throughout the whole process but also of the danger of such an impurity in materials containing large densities of extended defects generating recombination centers by means of the impurity-defect interaction.

Progress in Low-temperature Surface Passivation of Silicon Solar Cells using Remote-plasma Silicon Nitride

Using a remote-plasma technique as opposed to the conventional direct-plasma technique, significant progress has been obtained at ISFH in the area of low-temperature surface passivation of p-type crystalline silicon solar cells by means of silicon nitride (SiN) films fabricated at 350–400°C in a plasma-enhanced chemical vapour deposition system. If applied to the rear surface of the low-resistivity p-type substrates, the remote-plasma SiN films provide outstanding surface recombination velocities (SRVs) as low as 4 cm s−1, which is by a clear margin the lowest value ever obtained on a low-resistivity p-Si wafer passivated by a solid film, including highest quality thermal oxides. Compared to direct-plasma SiN films or thermally grown oxides, the remote-plasma films not only provide significantly better SRVs on low-resistivity p-silicon wafers, but also an enormously improved stability against ultraviolet (UV) light. The potential of these remote-plasma silicon nitride films for silicon solar cell applications is further increased by the fact that they provide a surface passivation on phosphorus-diffused emitters which is comparable to high-quality thermal oxides. Furthermore, if combined with a thermal oxide and a caesium treatment, the films induce a UV-stable inversion-layer emitter of outstanding electronic quality. Due to the low deposition temperature and the high refraction index, these remote-plasma SiN films act as highly efficient surface-passivating antireflection coatings. Application of these films to cost-effective silicon solar cell designs presently under development at ISFH turned out to be most successful, as demonstrated by diffused p-n junction cells with efficiencies above 19%, by bifacial p-n junction cells with front and rear efficiencies above 18%, by mask-free evaporated p-n junction cells with efficiencies above 18% and by MIS inversion-layer cells with a new record efficiency of above 17%. All cells are found to be stable during a UV test corresponding to more than 4 years of glass-encapsulated outdoor operation. © 1997 John Wiley & Sons, Ltd.