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.

 

Tandem Solar Cells: Working Principle, Structure, Efficiency & Advantages

 

Description 

Learn about tandem solar cells, their working principle, structure, efficiency, advantages, challenges, and future.

Introduction

The theoretical limits of single solar cell are 30%. The William Shockley and Hans Joachim Queisser made discovery about 50 years ago, called it Shockley – Quisser limit. They theoretically calculated that solar panels with one single layer suffer efficiency limitations as they are unable to absorb full solar light. In the tandem cell, two solar cells stack one on top of the other in which top cells are transparent, convert high energy photons into electricity. The bottom cell absorbs lower energy photons. The solar spectrum splits into two layers dramatically reduces thermalization losses. This will enable theoretically efficiency far better than single layer cells.

Operating Principle

In a tandem cell, the incident sunlight passes through the top sub cell first. High energy photons (blue and green wavelengths) are absorbed by the wide band gap perovskite layer, converting them at higher voltage similarly lower energy photons (red and near-infrared) transmitted through the top cell are captured by the silicon bottom cell. This spectrum splitting dramatically reduces thermalization losses in single junction cells.

Structure

The tandem devices are commonly fabricated in either two terminals or four terminals’ configurations. The sub cells are electrically connected in series and same current flows through all layers in the two terminals tandems. This design offers simple module integration and reduced wiring complexity but current matching between top and bottom cells.

The perovskite silicon tandem solar cells have strong efficiency potential. The perovskite layer absorbs high energy protons, while the silicon cell converts the lower energy photons. The structure of Perovskite tandem solar cell and function of each layer is explained here.

 

Structure of Perovskite Tandem solar cell

 

The function of each layer is given here.

 

Layer	Function
Glass substrate	Provide mechanical support and protects solar cell from environment
Anti reflection coating (ARC)	Minimizes light reflection and increases the amount of sunlight entering the cell
Transparent conductive oxide (TCO)	Conducts electrical current, when sunlight pass through it
Electron transport layer (ETL)	Extracts and transports electrons from the perovskite absorber to the electrode while blocking holes.
Perovskite absorber (Top Cell)	Absorbs high energy (short-wavelength) sunlight and generates electron-hole pairs
Hole transport layer (HTL)	Extracts and transports holes from the perovskite layer while blocking electrons
Recombination / Interconnection Layer	Electrically connects the top and bottom cells and enables carrier recombination between them
N type silicon layer	Selectively collects electrons and reduces recombination losses in the silicon cell.
Silicon absorber (Bottom Cell)	Absorbs lower energy (long wavelength) light that passes through the perovskite layer
P type Silicon Layer	Collects holes generated in the silicon absorber and transports them to the electrode
Rear TCO (if present)	Provides a conductive path and improves current collection.

 

Recombination Junction

The junction is the most critical component unique to tandem cells. It must allow electrons flow from the bottom sub cell to recombine with holes from the top sub cell (completing the internal circuit) with minimal optical absorption and electrical resistance. Transparent conductive oxides (ITO, AZO) or ultrathin metallic layers are commonly used.

Current Matching

In a two terminal series connected tandem, the sub-cell generating the lower photocurrent than total output — a condition known as current matching. The perovskite layer thickness and band gap must be precisely tuned so that both sub cells produce equal photocurrents under the AM1.5G (Air mass 1.5 Global) solar spectrum.

AM1.5G* - Air mass is the path length in which light takes through atmosphere normalized to the shortest possible path length to surface when sun is directly overhead. The 1.5 means sun light travelled through path length 1.5 times longer than direct overhead sunlight at sea level (AM 1.0G)

Salient Feature of the Perovskite Tandem Solar Cells

The following are the salient feature of the Perovskite Tandem Solar Cells.

•        The laboratory efficiency as per LONGI (Green energy Technology Company) achieves 33.9% efficiency in 2024.

•        The theoretical efficiency of two junction solar cell roughly 45% to 47% under concentrated sunlight.

•        It can capture both high energy and low energy solar photons

•        The standard monocrystalline silicon solar panel efficiency around 22 – 24% in commercial models. Its efficiency needs to reach around 33 – 36% to produce 50% more efficiency per unit area. An individual solar cell cannot achieve this due to Shockley – Queisser limit caps them at around 29.4%. The tandem solar cells drastically increase power output.

•        The perovkites degraded when exposed to heat, moisture, UV light during fabrication processes.

•        In a monolithic two terminal tandems, the entire device output is limited by lowest performing sub cell.

•        The mismatch of wavelength lead to unused photons resulting significant leakage current. 

FAQs 

What are tandem solar cells?

Tandem solar cells combine two photovoltaic materials to improve efficiency.

How efficient are tandem solar cells?

Laboratory efficiencies exceed 33%, with theoretical efficiencies of about 45–47% under concentrated sunlight.

Why is perovskite used?

It efficiently absorbs high-energy photons while silicon absorbs lower-energy photons.

What are the challenges?

Stability, moisture, UV degradation, and current matching.

Are tandem solar cells the future?

They are among the most promising next-generation solar technologies.

Perovskite Solar Cells: Structure, Working Principle, Advantages, Efficiency & Future (2026)

 

Introduction

Perovskite solar cells (PSCs) are among the most promising next-generation photovoltaic technologies. They use a metal-halide perovskite absorber with an ABX3 crystal structure. Since 2009, their certified efficiency has rapidly increased from 3.8% to over 26%, making them one of the fastest-developing solar technologies.

Structure of Perovskite Solar Cell

1. Glass Substrate

Mechanical support and light entry.

2. Transparent Conductive Oxide (ITO/FTO)

Transparent front electrode

3. Electron Transport Layer (TiO2/SnO2)

Extracts electrons

4. Perovskite Absorber Layer

Absorbs sunlight and generates charge carriers.

5. Hole Transport Layer

Extracts holes while blocking electrons

6. Metal Back Contact (Au/Ag)

Collects holes and completes the circuit.

Salient Features

·        Laboratory efficiency exceeds 26%

·        Band gap: 1.2–2.3 eV

·        High absorption coefficient enables very thin films

·        Low-temperature fabrication can reduce manufacturing costs

·        Suitable for tandem solar cells

Advantages

·        High efficiency

·        Low manufacturing cost potential

·        Lightweight and thin-film

·        Excellent low-light performance

Disadvantages

·        Long-term stability challenges

·        Moisture and heat sensitivity

·        Lead toxicity concerns

Applications

Building-integrated photovoltaics, portable electronics, tandem silicon-perovskite modules, and space applications

Conclusion

Perovskite solar cells have emerged as a leading photovoltaic technology due to their exceptional efficiency and low-cost manufacturing potential. Continued research is expected to improve durability and accelerate commercialization.

Frequently Asked Questions (FAQs)

1. What are Perovskite Solar Cells?

Perovskite solar cells are next-generation photovoltaic devices that use metal-halide perovskite materials as the light-absorbing layer.

2. How do Perovskite Solar Cells work?

They absorb sunlight in the perovskite layer, generate electrons and holes, and transport them through ETL and HTL to produce electricity.

3. What is the efficiency of Perovskite Solar Cells?

Laboratory-certified efficiencies have exceeded 26%.

4. What are the main layers?

Glass substrate, TCO, ETL, perovskite absorber, HTL, and metal back contact.

5. What are the advantages?

High efficiency, lightweight design, low-cost manufacturing potential, and tandem compatibility.

6. What are the disadvantages?

Moisture sensitivity, long-term stability issues, and lead-related concerns

7. Where are Perovskite Solar Cells used?

Building-integrated PV, tandem modules, portable electronics, and research applications

8. Can they replace silicon solar cells?

They are expected to complement silicon, especially in tandem solar cells.

9. Why are they important?

They promise higher efficiencies with potentially lower production costs.

10. What is the future scope?

Improved durability and commercial-scale production are expected to drive adoption.

 

 

FAME II Scheme Explained – Objectives, Incentives & Benefits

FAME II Scheme: Complete Guide to India’s Electric Vehicle Policy

The FAME II Scheme (Faster Adoption and Manufacturing of Electric Vehicles in India) is one of India’s most significant initiatives to promote electric mobility and reduce dependence on fossil fuels. The scheme encourages the adoption of electric vehicles through financial incentives, charging infrastructure development, and support for domestic manufacturing.

The Government of India launched this scheme to accelerate the transition towards clean transportation while reducing air pollution and greenhouse gas emissions.

What is the FAME II Scheme?

The FAME II Scheme is the second phase of the Faster Adoption and Manufacturing of Electric Vehicles (FAME India) programme. It was approved by the Cabinet Committee on Economic Affairs (CCEA) on 28 February 2019.

The scheme focuses on:

·        Promoting electric vehicles

·        Supporting EV manufacturing

·        Developing charging infrastructure

·        Reducing fuel imports

·        Encouraging sustainable transportation

Duration of FAME II Scheme

·        Launch Year: 2019

·        Duration: 5 Years

·        Total Budget Allocation: ₹10,000 Crore

·   Nodal Agencies: Ministry of Heavy Industries (MHI) and Bureau of Energy Efficiency (BEE)

Objectives of the FAME II Scheme

The major objectives include:

·        Encourage faster adoption of electric vehicles.

·        Strengthen India’s EV manufacturing ecosystem.

·        Reduce dependence on imported crude oil.

·        Lower greenhouse gas emissions.

·        Improve urban air quality.

·        Develop nationwide EV charging infrastructure.

·        Generate employment in the clean energy sector.

Strategic Goals of FAME II

The government has set ambitious goals under the scheme:

·        Achieve 30% electric vehicle penetration by 2030.

·        Increase investment in EV manufacturing and research.

·        Electrify public transport, including buses and three-wheelers.

·        Promote indigenous manufacturing through localization.

·        Position India as a global EV manufacturing hub.

Vehicle Deployment Targets

The FAME II Scheme supports large-scale deployment of electric vehicles across multiple categories.

Vehicle Category	Target
Electric Buses	7,090
Electric Three-Wheelers	5,00,000
Electric Four-Wheelers	35,000
Electric Two-Wheelers	10,00,000
Total Vehicles	Approximately 15.4 lakh

 

Charging Infrastructure Targets

To support EV adoption, the scheme includes extensive charging infrastructure development.

Key targets include:

·        Around 2,700 public charging stations

·        Charging station every 3 km in major cities

·        Charging station every 25 km on highways

·        Fast-charging corridors on major expressways

·        Smart grid-connected charging stations

Financial Allocation under FAME II

The ₹10,000 crore budget is distributed as follows:

Category	Allocation
Demand Incentives	₹8,596 Crore
Charging Infrastructure	₹1,000 Crore
Administration & Capacity Building	Remaining Budget

 FAME II Incentive Structure

Eligible electric vehicle buyers receive upfront subsidies based on battery capacity.

Electric Two-Wheelers (e-2W)

·        ₹15,000 per kWh

·        Maximum subsidy: ₹40,000

·        Minimum 40% localization required

Electric Three-Wheelers (e-3W)

·        ₹10,000 per kWh

·        Maximum subsidy: ₹50,000

·        Commercial vehicles only

Electric Four-Wheelers (e-4W)

·        ₹10,000 per kWh

·        Maximum subsidy: ₹1.5 lakh

·        Commercial and fleet vehicles only

Electric Buses

·        Up to ₹50 lakh subsidy per bus

·        Applicable for government procurement

Localization Requirements

The scheme encourages domestic manufacturing.

Major localization requirements include:

·        Motors

·        Motor Controllers

·        On-board Chargers

·        Battery Packs

·        Locally manufactured EV components

Vehicles failing to meet localization norms are not eligible for incentives.

Additional Benefits of FAME II Scheme

The policy also offers several additional benefits:

·        GST on EVs reduced from 12% to 5%

·        GST on EV chargers reduced to 5%

·        Income tax deduction up to ₹1.5 lakh under Section 80EEB

·        Road tax exemption in many states

·        Priority procurement of EVs by government departments

·        Financial support for charging infrastructure

Expected Impact of FAME II

The scheme is expected to create significant environmental and economic benefits.

Fuel Savings

Approximately 9.5 billion litres of fuel savings.

Reduction in Carbon Emissions

Around 2.5 crore tonnes of CO2 emissions expected to be reduced.

Employment Generation

Approximately 10 lakh direct and indirect jobs.

Foreign Exchange Savings

Reduction in crude oil imports leading to substantial foreign exchange savings.

Industry Growth

Private investment of over ₹50,000 crore expected in India’s EV ecosystem.

Advantages of the FAME II Scheme

·        Faster EV adoption

·        Cleaner environment

·        Lower fuel imports

·        Reduced pollution

·        Increased employment

·        Improved charging infrastructure

·        Growth of domestic EV manufacturing

Frequently Asked Questions (FAQs)

What is the full form of FAME II?

FAME stands for Faster Adoption and Manufacturing of Electric Vehicles in India.

Who launched the FAME II Scheme?

The Government of India launched the FAME II Scheme under the Ministry of Heavy Industries.

What is the budget of the FAME II Scheme?

The total financial outlay is ₹10,000 crore.

Who can receive FAME II incentives?

Eligible buyers of approved electric two-wheelers, three-wheelers, four-wheelers, and electric buses that satisfy localization requirements.

What is the main objective of the FAME II Scheme?

The primary objective is to accelerate electric vehicle adoption while promoting clean transportation and domestic EV manufacturing.

Conclusion

The FAME II Scheme represents a major milestone in India’s transition toward sustainable transportation. Through financial incentives, charging infrastructure, localization requirements, and manufacturing support, the scheme aims to accelerate EV adoption across the country. As India moves toward its clean energy goals, FAME II continues to play a vital role in reducing emissions, creating employment, and building a strong electric mobility ecosystem.