Bifacial Solar Cells: Structure & Working

 

Description

Learn about bifacial solar cells, their structure, PERC vs TOPCon architecture, bifacial gain, efficiency, and applications.

Introduction

Bifacial solar cells generate electricity from both their front surface (direct and diffuse sunlight) and their back surface (reflected albedo light from the ground and surroundings). Modern bifacial solar technology based on PERC (Passivated emitter and rear cell) and TOPCon (Tunnel oxide passivated contact) architectures, accounting for over 80% of new global PV installations as of 2024.

Structure

The standard bifacial PERC cell is built on a p type boron doped crystalline silicon wafer. The PERC innovation adds a dielectric passivation layer to the rear surface. The complete structure of PERC bifacial solar cell is explained here. 

 

 

 Structure of PERC Bifacial Solar Cell

 

1. Tempered glass with anti-reflection coating (front)

This glass protects the solar cell from environmental damage while allowing sunlight to enter. The anti-reflection coating minimizes light reflection, increasing the amount of light reaching the cell.

2. Silver busbars and finger contacts (front)

Silver fingers collect the electrical current generated by the cell and transport it to the busbars. The busbars carry the collected current to the external circuit with minimal electrical loss.

3. Silicon nitride (SiNx) anti-reflection layer

The silicon nitride coating reduces optical reflection and improves light absorption. It also provides surface passivation by reducing carrier recombination at the front surface.

4. n+ Emitter (Phosphorus Diffused)

The emitter is formed by diffusing phosphorus into the front surface of the silicon wafer. It creates the p–n junction where sunlight generates electron-hole pairs.

5. p-Type crystalline silicon Bulk

This layer acts as the main absorber of solar energy and generates most of the charge carriers. It provides the base material through which electrons and holes move toward their respective contacts.

6. Al₂O₃ / SiNx rear passivation stack

The rear passivation stack suppresses carrier recombination by passivating surface defects. It also reflects unabsorbed light back into the silicon, improving overall efficiency.

7. Local Aluminum BSF contacts

Aluminum is deposited only at localized openings in the passivation layer to form the back surface field (BSF). This structure improves carrier collection while maintaining excellent rear surface passivation.

8. Open rear contact grid

The rear metal grid provides electrical conduction while leaving much of the rear surface open for light entry. This open structure allows the cell to generate electricity from reflected sunlight reaching the rear side.

PERC Versus TOPCon Architecture

Standard PERC uses an Al2O3/SiNx dielectric passivation layer with local laser drilled contact openings. TOPCon (Tunnel Oxide Passivated Contact) upgrades this with an ultra-thin (~1.5 nm) silicon oxide tunnel layer plus a heavily doped polysilicon layer, providing full area rear passivation — achieving cell efficiencies of 24–25% versus ~23% for standard PERC. TOPCon is now replacing PERC as the new baseline technology across major manufacturers.

Bifacial Gain

The additional energy contributed by the rear surface is termed as the bifacial gain (BG), which depends on the bifacial factor of the cell (typically 70–90%) and the ground albedo coefficient (the fraction of sunlight reflected by the ground surface). The annual bifacial gain typically ranges from 5% (dark soil) to 30% (white gravel, snow, or white rooftop membrane).

Salient feature of the bifacial solar cells

The following are the salient feature of the bifacial solar cells

• The efficiency of single bifacial solar cell is in the range of 22 to 25%
• The TOPCon bifacial solar cell module power output range from 400 to 660 W
• The bifacial gain of 5% to 30% due to additional energy from rear (back) side of the solar cell.
• The temperature coefficient is -0.35%/°C (PERC), -0.30%/°C (TOPCon) solar cell.
• The bifacial solar cell has achieved 80% market share as per 2024 data.
• The ideal installation of bifacial solar panel is on the ground mounted and elevated racking where reflected albedo surface.

FAQs

What is a bifacial solar cell?

It generates electricity from both front and rear surfaces.

What is bifacial gain?

Extra energy generated from reflected light reaching the rear side.

What is the difference between PERC and TOPCon?

TOPCon offers better passivation and higher efficiency than PERC.

Where should bifacial panels be installed?

On elevated or ground-mounted systems with reflective surfaces.

What is the efficiency of bifacial solar cells?

Typically 22–25% for commercial cells.