The solar industry’s road for solar panels with a higher power is paved with different solar cell technologies that attempt to reduce power losses, increase efficiencies, and reduce production costs for photovoltaic (PV) modules. One of the most innovative methods to have proven higher efficiencies using crystalline silicon (c-Si) cells is the Interdigitated Back Contact (IBC) solar cell technology.
IBC solar cell technology has proven to be superior to traditional Aluminum Back Surface Field (Al-BSF) options, but it has the downside of having a more expensive and complex manufacturing process. In this article, we explain everything about IBC technology, including the components, structure for IBC solar cells, operating principle, and even compare IBC against other PV technologies.
Table of Contents
What is an IBC solar cell and how does it work?
IBC solar cell technology restructures components in the solar cell and includes additional ones to increase efficiency for the cell, and provide additional benefits. In this section, we explain the materials and the structure of IBC solar cells, and we explain the operating principle for the technology.
Materials & components of the IBC solar cell
The main component featured in most IBC solar cells is a c-Si wafer that acts as the n-type wafer absorber layer, but p-type wafers are also used. Monocrystalline silicon (mono c-Si) is the most common option due to its higher efficiency, but polycrystalline silicon (poly c-Si) can also be used.
An anti-reflective and passivation layer is placed on one of the two sides of the c-Si wafer, being manufactured with a thin layer of silicon dioxide (SiO2) placed through a thermal oxidation process. Materials like Silicon Nitride (SiNx) or Boron Nitride (BNx) are also suitable.
For IBC solar cells to relocate frontal contacts at the rear side of the cell, they require interspersed or interdigitated layers of n+ and p+ emitters called the diffusion layer. To create it, layers of the n-type wafer are doped with boron through masked diffusion, masked ion-implantation, or laser doping, creating the p-type (p+) digitation, while the n-type layers stay intact (n+).
Metal contacts are also placed by laser ablation or wet chemical deposition, using regular metals like silver, nickel, or copper for the contacts of the IBC solar cell.
This is one of the most popular approaches for manufacturing IBC solar cells, but there are different approaches available (Figure 1), which might require different materials for manufacturing the diffusion layer.
Structure of the IBC solar cell
Manufacturing IBC solar cell can be quite complex considering the creation of the diffusion layer, but understanding its structure is relatively simple.
The main layer for the IBC solar cell is the n-type or p-type c-Si wafer functioning as the absorber layer. This layer is manufactured by doping a c-Si layer with boron or phosphorous, to create a p-type or n-type doped wafer. Then, an anti-reflective and passivation coat usually made out of SiO2 is placed on one or two sides of the solar cell (Figure 2).
The major structural design modification for the IBC solar cells is the inclusion of a diffusion layer, which features interdigitated n-type and p-type layers allowing for the installation of rear side metal contacts (Figures 2 & 3).
Finally, every metal contact for the IBC solar cell is placed in the back of the cell, leaving the front of the cell entirely free from shading materials. This also allows for installing contacts in a wider area, causing series resistance for the cells to be lowered.
Working principle of the IBC solar cell
IBC solar cells generate solar power under the photovoltaic effect as Al-BSF solar cells do. The load is connected between positive and negative terminals of the IBC solar panel, with photons being converted into electricity, creating solar power to energize the load.
Alike traditional solar cells, photons impact the IBC solar cell absorber layer, exciting electrons and creating an electron-hole (e-h) pair. Since IBC solar panels do not feature frontal metal contacts that shade the cells, these solar cells have a higher area of conversion for photons to impact.
The e-h pair formed at the front of the IBC solar cell is then collected by a p-type interdigitated layer at the back. Collected electron flows from p+ metal contacts to the load, generating electricity, and then going back to the IBC solar cell through the n+ metal contact, ending that particular e-h pair.
IBC solar cells vs. Traditional cells
After understanding more about IBC solar cells, it is important to compare them to the well-known traditional Al-BSF technology. In this section, we compare both options considering different aspects.
| Aluminum Back Surface Field (Al-BSF) | Interdigitated Back Contact (IBC) | ||
| Monocrystalline Silicon (mono c-Si) | Polycrystalline Silicon (poly c-Si) | ||
| Structure (Contact Positioning) | Front/rear side | Front/rear side | Rear side |
| Aesthetics | Traditional aesthetic (showing front contact) | Traditional aesthetic (showing front contact) | Increased aesthetic (no visible contacts) |
| Highest Recorded Efficiency | 25.4% | 24.4% | 26.7% |
| Lifespan | 25-30 years | 30 years | |
| Temperature Coefficient | -0.446 %/ºC | -0.387 %/ºC | -0.29%/ºC |
| Price | $0.16/W -$0.46/W | $0.24/W | $0.30/W1 |
| Applications | Residential & Industrial | Residential & Industrial | Residential, Industrial, and Concentrated Photovoltaic (CPV) |
One structural problem that IBC solar cells improve from the design of traditional Al-BSF cells, is removing the front metal contact at the cell. This provides two advantages for IBC solar cell technology: reduced shading by locating metal contacts at the rear side of the cell and increasing power density by allowing installation of solar cells without space in between on the IBC solar panel.
Due to the improvements in IBC solar cells, IBC technology has achieved a recorded efficiency of 26.7%, which is 1.3% more than traditional technologies. IBC solar cell technology does not stop there, since researchers expect to achieve an efficiency of 29.1% for IBC solar cells.
IBC solar cell technology improves the temperature coefficient from -0.387%/ºC to -0.446%/ºC for traditional options, down to -0.29%/ºC. As a result, an IBC solar panel can deliver a better performance in hot climate installation.
While IBC solar cell had a high production cost and features a complex manufacturing process, the cost for this technology has been reduced to $0.30/W. With higher efficiency and only a slightly higher price, IBC solar cell technology is a compelling option for residential and industrial applications, which could cause IBC technology to take control of around 35% of the market share by 2025.
While Al-BSF and IBC solar panels can be used for residential and industrial applications, IBC solar cell technology has the upper hand in CPV applications. This is caused by IBC solar panels having a lower series resistance, higher bulk lifetime, and lower surface recombination, making it ideal for these applications with increased solar concentration which provides several interesting advantages.
IBC solar cells vs. PERC cells
Passivated Emitter and Rear Contact (PERC) and IBC solar panels share interesting design improvements from Al-BSF technology. Both technologies share higher efficiencies, better temperature coefficients, and larger areas for photon absorption.
PERC and IBC technologies share the reduction of the surface area occupied by the busbars or metal contacts, delivering similar advantages. While PERC technology only reduces the busbars, IBC solar panel technology eliminates it, further increasing the effective surface area for photon absorption.
IBC technology surpasses PERC technology in its efficiency, due to PERC technology only achieving an efficiency of 25.4%, while IBC solar panel technology achieved recorded efficiencies of 26.7%.
The major point in favor of PERC against IBC solar cell technology is that IBC technology is more expensive to manufacture than PERC technology.
While both technologies have their differences, they are an improvement from traditional Al-BSF options, and the major point in favor of both is that they can be combined. This opens a way for the creation of PERC-IBC solar panels, featuring additional advantages against traditional technologies.
Roundup: The benefits of IBC solar cells
IBC solar panels have many benefits that make them outstand from traditional Al-BSF technology and others. In this section, we round up the benefits of IBC solar cell technology.
Reduced losses by shading
IBC solar cell restructuration places frontal metal contact on the rear side of the cell, eliminating shade caused by the busbars. By doing this, IBC solar cell increases the photon effective absorption which results in reduced power losses and several other benefits.
Reduced series resistance
IBC solar cells lower the series resistance at the cell from traditional Al-BSF cells, by being able to place larger metal contacts at the rear side of the cell, becoming a key factor for CPV applications.
Increased power output per square meter
With an increased efficiency for IBC solar cells, an IBC solar panel can be manufactured without space between cells, further increasing the power output per square meter for a single module. This makes IBC solar cell technology more compelling for applications with limited space.
Independent optical/electrical optimizations
Since IBC solar cells relocate metal contacts at the back, the optical and electrical optimizations for the cell are decoupled, making each optimization completely independent from the other, making it easier for researchers to improve one or the other separately.
Who manufactures IBC panels?
IBC solar panels are manufactured by a few companies in the US, with the two most popular ones being SunPower and Trina Solar.
SunPower: Maxeon® solar panels
SunPower is a solar company manufacturing solar panels in the US for more than 35 years. This company delivered the first commercial IBC solar panels to the US, producing high-quality modules with excellent performance, with their Maxeon® solar panels.
Maxeon solar panels achieved one of the highest efficiencies for PV modules in the market. These modules feature a copper substrate that increases strength and resistance to corrosion, featuring high-quality silicon layers for the solar cells that produce 60% more power than other technologies in the market.
Trina Solar
Trina Solar has provided some of the most cost-effective solar solutions in the US solar market for around 25 years, ideal for residential, commercial, and utility-scale applications. The company focuses on improving PV technology, known for setting a new record for mono c-Si IBC solar cells in 2018.
This company is one of the largest IBC solar panel producers in the US. Trina Solar has shipped over 80GW in solar panels worldwide and performed grid-tied installations for over 5.5GW in the US.
