?Next PV Module Mainstream

In recent years, a large number of technologies and sub-technologies have emerged to enhance the efficiency and production of photovoltaic modules. The main goal of these innovations and technologies is to maximize the performance of the photovoltaic module.

In the simplest, the performance of a module can be translated into #powerdensity, which is the power output relative to the module's dimension. Therefore, power density means more out per unit area.

However, efficiency is not the only parameter for choosing one module over another. Other considerations include price, degradation, temperature coefficient, etc. If this is of interest it can be addressed in another article.

Below are summarized the four main solar module technologies:

PERC (Passivated Emitter Rear Contact)

PERC technology, widely used from 2017 to 2022, combines rear surface passivation and local rear contacts (Al?O?). The dielectric passivation layer improves electron movement within the cell and reflects light into the cell, giving the cell a second chance to capture electrons that would otherwise simply pass through.

PERC technology increases power density and efficiency while reducing module temperature because the sunlight that was previously not absorbed would be converted into heat. Though still in use, PERC has lost market share to technologies like #topcon, #HJT, and #XBC in 2023.

TOPCon (Tunnel Oxide Passivated Contact)

It is said that #TOPCon is the natural transaction from P-Type (PERC) technology), because both cell structures are very similar (texturing, diffusion, etching...), TOPCon technology started gaining market share above all in 2023, providing greater efficiency than PERC. Using n-type cells, TOPCon technology adds an ultrathin silicon oxide layer and phosphorous-doped poly-Si layer.

Benefits????

• Higher efficiency compared to the P-Type PERC technology;
• The silicon oxide layer uses the quantum tunneling effect to transfer current without the electrode coming into contact with the wafer of silicon, which reduces the loss of efficiency;
• Switch to using n-type Si-wafer which results in lower degradation over time (no boron-oxygen complexing in Si-bulk).

Drawbacks????

• Front contact is not passivated, so front-side recombination losses remain due to boron diffusion and metal/Si contact areas.
• It has burbars on the front side which lead to optimal shading losses between 3-5% compared to Back Contact technology.
• The n-poly-Si layer is added during the annealing process at a very high temperature, between 850-1000oC, which can lead to the generation of concentric circles in the cell.
• Extra silver is needed for front metal compared to PERC, meaning extra cost
• It is not possible to improve cell efficiency beyond 26%.
• The aluminum oxide passivation layers in TOPCon cells are prone to UV degradation. While PERC technology is not significantly affected due to the aluminum being on the back side, TOPCon is more sensitive because the aluminum oxide passivation layers are located on the light-exposed front side.

Back Contact Technology

In the 1970s, SunPower introduced the concept of back-contact solar cells and developed interdigitated back-contact (IBC) solar cells. The most significant features of IBC cells are the absence of front metal contact and isolated P and N regions arranged in interdigitated patterns at the rear side where metal contacts are attached.

XBC solar cells are c-Si wafers that act as n-type wafer absorber layers, but p-type wafers are also used. Then an anti-reflective and passivation coat usually made out of SiO2 is placed on one or both sides of the solar cells. The major structural design modification for XBC solar cells is the inclusion of a diffusion layer, which features interdigitated n-type layers allowing for the installation of the rear side metal contacts.

Benefits ????

• Higher power efficiency ???? no front shading contributes to high conversion efficiency.
• Reduction in series resistance because of placing larger metal contacts at the rear side of the cell.
• Increase Power Output per square meter since XBC is manufactured without space between cells thanks to all contacts being on the rear side ???? more compelling for applications with limited space.
• High reliability???? full-back-side soldering technology with minimal risk of cell cracking.
• Good aesthetics thanks to the absence of metal contact patterns on the front side make it suitable for PV applications.

Drawbacks????

• Complex architecture and difficult manufacturing processes resulted in high costs and difficulties in industrialization. Therefore, XBC manufacturers need to possess comprehensive capabilities (doping, deposition of passivation layers, metallization, rear patterning, and selective etching technologies).
• The practical limit of c-Si solar cells is 27.5%

Heterojunction

#HJT Technology combines two different technologies, crystalline and amorphous materials in a single cell. A crystalline silicon cell, normally Type N, inserts two layers of “thin film” amorphous silicon. The intrinsic quality of the a-Si layer is essential for the passivation effect. It also has another layer of #TCO to conduct current.

Benefits????

• Both the front and rear sides of the wafer are passivated by undoped amorphous silicon (a-Si) layers, while entirely avoiding diffusion.
• Hole/electron collection on the front/rear ensured by p-type/n-type a-Si, all deposited using the same equipment as undoped a-Si.
• Extremely good Si surface passivation enabling world record high open circuit voltages and efficiencies higher efficiency compared to the P-Type PERC technology

Drawbacks ????

• a-Si and transparent conductive oxides (TCOs) such as indium tin oxide (ITO) needed to collect current at metal contacts ????challenges optical transparency of an a-Si and TCO + costs of indium.
• Low-temperature silver paste is needed for metallization on temperature-sensitive of a-Si layers ????inferior conductivity compared to high-temperature metallization used in PERC and TOPCon.
• More silver is needed when compared to TOPCon ???? extra costs
• Equipment needed for a-Si deposition needs regular cleaning.
• It has burbars on the front side which leads to optimal shading losses between 3-5% compared to Back Contact technology.

How are ranked these technologies?

Now, all these technologies show many benefits in terms of efficiency and improvement over the time, nevertheless, taking into consideration the ranking of TaiyangNews from June 2024, from Top ?? to ??are #backcontact technology.