Interdigitated Back Contact Solar Cells Research Articles

Ion Implantation for All-alumina IBC Solar Cells with Floating Emitter

Interdigitated back contact (IBC) solar cells have a high efficiency potential. However, the fabrication of this cell structure is quite complex. Ion implantation for structured doping together with batch reactors for front and rear side passivation with Al2O3 could help to reduce the fabrication effort. Since Al2O3 gives a very good passivation on p-doped surfaces, we investigate n-type IBC solar cells with a low-dose ion-implanted front floating emitter (FFE) which we compare to a low-dose ion implanted front surface field (FSF) passivated by SiO2. We measured saturation current densities (J0) between 10 and 15 fA/cm2 for the SiO2 passivated FSF and down to 5 fA/cm2 for the Al2O3 passivated FFE on textured samples. The FFE has been successfully applied to fully implanted IBC cells (η = 21.8 %). Cells with FSF degraded strongly under UV-illumination due to the instable SiO2 passivation on the front side while the FFE cells with Al2O3 passivation were much less affected. IV measurements under low level illumination revealed a linear performance down to 0.01 suns for both, FSF and FFE.

Boron Implanted, Laser Annealed p+ Emitter for n-type Interdigitated Back-contact Solar Cells

Ion implantation and laser processing technologies are very attractive for the fabrication of industrially feasible interdigitated back-contact (IBC) solar cells. In this work, p+ emitters were fabricated by boron implantation and laser annealing, and the electrical properties of emitters were investigated. An emitter sheet resistance (Rsh) in the range of 30-200Ω/□ could be achieved by varying the implanted dose. The saturation current density (Joe) of the passivated p+ emitter with Rsh of ∼125Ω/□ reached 95 fA/cm2, and the contact resistivity was determined to be as low as 5×10-6Ω·cm2. Such localized p+ emitters can be applied to n-type IBC solar cells, which could avoid the high temperature thermal annealing step and related problems.

Capillary flow of amorphous metal for high performance electrode

Metallic glass (MG) assists electrical contact of screen-printed silver electrodes and leads to comparable electrode performance to that of electroplated electrodes. For high electrode performance, MG needs to be infiltrated into nanometer-scale cavities between Ag particles and reacts with them. Here, we show that the MG in the supercooled state can fill the gap between Ag particles within a remarkably short time due to capillary effect. The flow behavior of the MG is revealed by computational fluid dynamics and density funtional theory simulation. Also, we suggest the formation mechanism of the Ag electrodes, and demonstrate the criteria of MG for higher electrode performance. Consequently, when Al85Ni5Y8Co2 MG is added in the Ag electrodes, cell efficiency is enhanced up to 20.30% which is the highest efficiency reported so far for screen-printed interdigitated back contact solar cells. These results show the possibility for the replacement of electroplating process to screen-printing process.

Optimization of Metal Coverage on the Emitter in n-Type Interdigitated Back Contact Solar Cells Using a PC2D Simulation

In interdigitated back contact (IBC) solar cells, the metal-electrode coverage on a p-type emitter is optimized by a PC2D simulation. The result shows that the variation of the metal coverage ratio (MCR) will affect both the surface passivation and the electrode-contact properties for the p-type emitter in IBC solar cells. We find that when Rc ranges from 0.08 to 0.16Ω·cm2, the MCR is optimized with a value of 25% and 33%, resulting in a highest energy-conversion efficiency. The dependences of both Voc and fill factor on MCR are simulated in order to explore the mechanism of the IBC solar cells.

Large-Area Back-Contact Back-Junction Solar Cell With Efficiency Exceeding 21%

In this study, high-efficiency solar cells are presented with the use of low-cost industrially available technologies. This results in the so-called ZEBRA concept: a litho-free process in which standard 156 × 156 mm2 monocrystalline n-type Cz-Si wafers are processed into high-efficiency interdigitated back-contact solar cells. In our first attempt, we obtained energy conversion efficiencies of more than 20% on 239 cm2 area. With the help of a 3-D simulation of the device, a further improvement to more than 21.5% was determined.We indentify the open-circuit voltage and the large serial resistance as the main losses impeding from reaching the simulated efficiency. The cell results after an extensive optimization are presented in this study, focusing on the improvement of the fill factor of the cells. The optimized solar cells show an improvement in the energy conversion efficiency up to 21%. Furthermore, the simplemetallization and themodule interconnection design of the ZEBRA cells allow for a bifacial application. Indoor and outdoor I – V measurements on a bifacial one-cell-module show an enhancement in the total generated power of more than 12% as compared with a monofacial module.

The Emitter Having Microcrystalline Surface in Silicon Heterojunction Interdigitated Back Contact Solar Cells

In producing the Si heterojunction interdigitated backcontact solar cells, we investigated the feasibility of applying amorphous Si emitter having considerable crystalline Si phase at the facing to transparent conducting oxide (TCO) layer. Prior to evaluating electrical property, we characterized material nature of hydrogenated microcrystalline p-type silicon (µc-p-Si:H) as crystallized fraction, surface morphology, bonding kinds in thin films and then surface passivation quality finally. The diode and interface contact characteristics were induced by the simple test device and then current–voltage (I–V) curve showed more linearity in µc/hydrogenated amorphous silicon (a-Si:H) emitter case. We fabricated heterojunction back contact (HBC) solar cells using p/n interdigitated structure and acquired the 23.4% efficiency in cell size with performance parameters as open-circuit voltage (Voc) 723 mV, short-circuit current density (Jsc) 41.8 mA/cm2, fill factor (FF) 0.774, in the cell size (at 2×2 cm2).

The Emitter Having Microcrystalline Surface in Silicon Heterojunction Interdigitated Back Contact Solar Cells

In producing the Si heterojunction interdigitated backcontact solar cells, we investigated the feasibility of applying amorphous Si emitter having considerable crystalline Si phase at the facing to transparent conducting oxide (TCO) layer. Prior to evaluating electrical property, we characterized material nature of hydrogenated microcrystalline p-type silicon (µc-p-Si:H) as crystallized fraction, surface morphology, bonding kinds in thin films and then surface passivation quality finally. The diode and interface contact characteristics were induced by the simple test device and then current–voltage (I–V) curve showed more linearity in µc/hydrogenated amorphous silicon (a-Si:H) emitter case. We fabricated heterojunction back contact (HBC) solar cells using p/n interdigitated structure and acquired the 23.4% efficiency in cell size with performance parameters as open-circuit voltage (Voc) 723 mV, short-circuit current density (Jsc) 41.8 mA/cm2, fill factor (FF) 0.774, in the cell size (at 2×2 cm2).

Contacting Interdigitated Back-Contact Solar Cells With Four Busbars for Precise Current–Voltage Measurements Under Standard Testing Conditions

Increasing the area of interdigitated back-contact (IBC) solar cells featuring a busbar contact geometry requires the use of longer fingers. The finger resistance will, thus, be increased if the thickness of the metallization is kept constant. In order to maintain a thin metallization, it is beneficial to increase the number of busbars per contact. However, using more than one busbar for each polarity implies an asymmetric contact geometry. As a consequence, under operation, the busbars of the same polarity carry different currents. Due to voltage drops over unavoidable electrical resistances, this may lead to significant potential differences between these busbars. Since current–voltage characteristics are usually measured using separate sense contacts for the voltage measurement, the position and number of these contacts may considerably affect the shape of the resulting current–voltage characteristic and, thus, the fill factor. By means of simulations with the circuit simulator LTSpice, we show that a permanent contacting with soldered tabs allows for a correct determination of the fill factor. A chuck used for temporary contacting should feature at least one sense contact per busbar and pin contacting resistances below 30 mΩ in order to keep the fill factor error below 0.5% absolute.

Simple power-loss analysis method for high-efficiency Interdigitated Back Contact (IBC) silicon solar cells

A simple analytical method is presented to perform a power-loss analysis of high-efficiency silicon Interdigitated Back Contact (IBC) solar cells. The method assumes one-dimensional current flows for both minority and majority carriers, as well as a constant gradient (or linear profile) of minority carrier concentration from the front to the back of the solar cell. The power-loss analysis method is applied to a real IBC silicon solar cell with a conversion efficiency of 23.3%.

Screen-Printed Aluminum-Alloyed $\hbox{P}^{+}$ Emitter on High-Efficiency N-Type Interdigitated Back-Contact Silicon Solar Cells

We demonstrate the use of industrial-orientated screen-printed aluminum-alloyed emitter for high-efficiency n-type interdigitated back-contact silicon solar cells. Different cell designs with various pitch sizes and emitter fractions have been studied. With an improved front surface field (FSF), short-circuit current densities up to 40 can be obtained. By combining the best cell design and the improved FSF, a high conversion efficiency of 19.1% with Czochralski n-type material has been achieved.

Realization of Self-Aligned Back-Contact Solar Cells

Among high-efficiency cells, interdigitated back-contact (IBC) solar cells present many advantages over conventional structures. In most cases, fabrication processes involving many masks and alignments are needed. In this paper, we present an alternative approach to simplify the IBC solar cell fabrication process. Here, only one mask without alignment was used to define the total solar cell. Separation between emitter and base comb is reached by cantilevers which prevent interconnections during Al deposition. Cantilevers are formed by a low-cost chemical etching solution. With this process, we have obtained cells with a fill factor of 77%.

MIS-stimulated back-surface passivation of interdigitated back-contacts solar cells

The possibility of surface recombination losses reduction on the rear side of interdigitated back-contact solar cells by field-effect passivation is investigated. To provide field-effect passivation, an additional biased metal/insulator/semiconductor (MIS) structure is formed between n ++ and p + -doped regions. The source of the bias is the potential that appears in the solar cell under illumination. Two-dimensional (2D) numerical simulations were performed to determine the best passivation conditions. In particular, the influence of symmetric and asymmetric capture cross sections for electrons and holes at the rear side of the cell is simulated and the advantage of symmetric capture cross section for this type of passivation is discussed. Experimental and calculated data are compared for Si/SiO 2 interface.

Measurement of diffusion length and surface recombination velocity in Interdigitated Back Contact (IBC) and Front Surface Field (FSF) solar cells

A method is proposed for measuring the diffusion length and surface recombination velocity of Interdigitated Back Contact (IBC) solar cells by means of a simple linear regression on experimental quantum efficiency values versus the inverse of the absorption coefficient. This method is extended to the case of Front Surface Field (FSF) solar cells. Under certain conditions, the real or the effective surface recombination velocity may be measured.

Determination of diffusion length and surface recombination velocity in interdigitated back contact (IBC) solar cells

A method is presented for measuring the diffusion length and surface recombination velocity of Interdigitated Back Contact (IBC) solar cells. The quantum efficiency of these cells can, under appropriate conditions, be approximated by a linear relationship with respect to the inverse of the absorption coefficient. A simple linear regression on experimental values allows to determine the surface recombination velocity and the diffusion length. Experimental results are presented for some IBC and Front Surface Field (FSF) solar cells.

An interdigitated back contact solar cell with high-current collection

Internal current-collection efficiencies greater than 90 percent and energy-conversion efficiencies of 18-percent at 30 suns have been measured on a laboratory version of the interdigitated back contact (IBC) solar cell. The quantum efficiency at 600 nm was greater than 90 percent which implies a minority carrier lifetime of greater than 350 µsec and a front surface recombination velocity of less than 30 cm/sec on the better devices. The processing steps on which the high-current collection in the IBC cell depends will be discussed.