Guides · Faisalabad, Lahore, Punjab
TOPCon vs HJT vs Back-Contact Panels
Short answer
TOPCon, HJT (heterojunction) and back-contact (BC) are the three main N-type cell designs in today's solar panels. TOPCon is the mainstream choice with the best value per watt; HJT usually has the best heat behaviour and rear-side (bifacial) output but costs more and is less common in Pakistan; back-contact gives the highest front-side efficiency and a clean all-black look, at a higher price per watt and with less bifacial gain. For most Punjab homes and factories, a genuine panel of any of the three, correctly installed, will serve well. The right choice depends on roof space, structure height and budget.
This guide assumes you already know what N-type means. If not, start with N-type vs P-type and bifacial panels.
How each design is built, in brief
TOPCon (tunnel oxide passivated contact)
TOPCon adds an extremely thin oxide layer and a layer of doped silicon at the back of an N-type cell. This reduces the energy lost where the metal contacts touch the silicon. The process is an upgrade of the older PERC production lines, so manufacturers could scale it quickly and cheaply. That is why most N-type panels sold today are TOPCon. Industry analysts put TOPCon at roughly 70% of the market by the end of 2024.
HJT (heterojunction)
HJT sandwiches a crystalline N-type wafer between very thin layers of amorphous silicon. The structure is symmetrical, so HJT cells are naturally bifacial, and they keep their output well in heat. The drawbacks are cost (special equipment and more silver or alternative metals) and smaller production volumes, so HJT panels are less common in the Pakistani market.
Back-contact (BC, including HPBC and ABC)
A back-contact cell moves all its electrical contacts to the rear. With no metal lines on the front, more of the surface catches light, which gives high front-side efficiency and a uniform dark look. LONGi uses this approach in its HPBC ranges and AIKO across its ABC range. Back-contact cells are harder to make, so the price per watt is usually higher, and their rear side collects less light than TOPCon or HJT.
TOPCon, HJT and back-contact
TOPCon
Mainstream N-type
HJT
Low temperature loss
Back-contact
No front busbars
Side-by-side comparison
Ranges below are typical published figures for commercial modules, for orientation only. They differ by source and product generation.
| TOPCon | HJT | Back-contact | |
|---|---|---|---|
| Typical module efficiency | About 22 to 24% | About 23 to 25% | About 24 to 25% |
| Temperature coefficient of Pmax | About −0.28 to −0.32%/°C | About −0.24 to −0.27%/°C | About −0.24 to −0.29%/°C |
| Bifaciality (rear vs front) | Around 75 to 85% | Around 85 to 95% | Lower; varies widely by generation |
| Price per watt | Lowest of the three | Higher | Highest, usually |
| Availability in Pakistan | Widest | Limited | Good from LONGi and AIKO |
| Best suited to | Most roofs and large arrays | Hot sites, elevated or ground mounts | Small or visible roofs, tight spaces |
Efficiency is explained in solar panel efficiency: what the percentage means. Remember that higher efficiency means more watts per square metre, not more units per kW.
What the differences mean on a Punjab roof
Heat
Punjab summers push cell temperatures well above the 25°C used in testing. A temperature coefficient closer to zero means less power lost at midday.
For example, if cells reach 65°C (40°C above test temperature), a panel at −0.30%/°C loses about 12% of its rated power at that moment, while one at −0.25%/°C loses about 10%. Over a whole summer that gap is real but modest, and good airflow under the panels can matter as much. See solar panels in Punjab summer heat.
Bifacial gain on elevated structures
If you are building an elevated structure over a white or light roof, the rear of a bifacial panel can add output. TOPCon and especially HJT have high bifaciality; back-contact panels generally have less. On a low structure over a dark roof, the rear gain is small for all three. See bifacial panels on white roofs and elevated structures and L2, L3 and elevated structures.
Partial shading
Some back-contact makers claim better output under partial shade, because of how their cells and bypass circuits are arranged. Treat this as a model-specific claim to check on the datasheet, not a general rule. On any panel, a water tank shadow across one row still costs output. See how shading cuts solar output and bypass diodes and junction boxes explained.
Price per watt and roof space
On a large, open factory roof, TOPCon usually gives the most kW for the money. On a small home roof with tanks and a stair tower, a back-contact panel can fit more kW in the usable space, which may justify its higher price per watt. Compare today's rates on our solar panel price in Pakistan page.
Reliability and build quality
Independent testing finds that build quality varies between factories more than between cell types. A genuine panel from an established manufacturer, with its warranty in writing, matters more than the cell label. Always check the serial number: see how to check genuine solar panels.
Which approved brands use which design
| Brand | Range commonly seen in Pakistan | Cell design | More |
|---|---|---|---|
| JinkoSolar | Tiger Neo | N-type TOPCon | JinkoSolar panels |
| JA Solar | DeepBlue 4.0 | N-type TOPCon | JA Solar panels |
| Canadian Solar | TOPBiHiKu and others | N-type TOPCon | Canadian Solar panels |
| LONGi | Hi-MO X10, Hi-MO 9 | Back-contact (HPBC 2.0) | LONGi panels |
| AIKO | Neostar, Comet | All-back-contact (ABC) | AIKO panels |
| Cora Dawn, Jasco | Per model | Ask for the datasheet |
Ranges available change with distributor stock. For a fair brand comparison, see best solar panels in Pakistan.
Which should you choose?
| Your situation | Sensible starting point |
|---|---|
| Large factory roof or ground array, budget-led | TOPCon, bifacial if the structure is raised |
| Elevated structure over a white roof | TOPCon bifacial, or HJT if available at a sensible price |
| Small home roof, space is the limit | Back-contact or top-efficiency TOPCon |
| Visible roof where looks matter | All-black back-contact |
| Very hot site with good airflow | Any; HJT and BC have a slight heat advantage on paper |
Do not mix cell types or wattages in one string. Each string should use identical panels.
How Solar Works Pakistan chooses the cell type
Our in-house engineers compare panels on price per watt, efficiency, temperature behaviour and bifaciality against your roof layout and structure, then name the exact brand and model in the quotation. We design structures in-house and our teams fabricate and assemble them on site, with a 3-year structure warranty. Panels carry their manufacturer's warranty per product.
Get today's price or a free site survey
Tell us your roof size and structure plan, and we will suggest which cell type fits, with today's rates.
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM daily
We serve customers throughout Punjab, with site surveys normally free. See our Faisalabad and Lahore pages, or contact us.
Frequently asked questions
Is TOPCon or HJT better?
HJT usually handles heat slightly better and has higher bifaciality, while TOPCon costs less per watt and is far more widely available. For most roofs in Punjab, TOPCon is the practical value choice; HJT can make sense on elevated or ground mounts if priced sensibly.
Is back-contact better than TOPCon?
Back-contact panels give more watts per square metre and a cleaner look, which helps on small or visible roofs. On large open roofs, TOPCon usually gives more kW for the same budget, and it collects more light from the rear on elevated structures.
Are LONGi Hi-MO X10 panels TOPCon?
No. The Hi-MO X10 uses LONGi's back-contact cell design (HPBC 2.0). JinkoSolar's Tiger Neo and JA Solar's DeepBlue 4.0 are TOPCon.
Are back-contact panels bifacial?
Some are offered in bifacial versions, but their rear-side output is generally lower than TOPCon or HJT. Check the bifaciality figure on the exact model's datasheet.
Does HJT perform better in Pakistan's heat?
On paper, HJT panels usually have a temperature coefficient closer to zero, so they lose a little less power on hot afternoons. Mounting with good airflow also makes a meaningful difference for any panel.
Can I mix TOPCon and back-contact panels in one system?
Not in the same string. Different panels have different voltages and currents. They can sometimes be used on separate inverter inputs if the design allows, which your engineer should check.
Sources
- EnergyTrend, analysis of TOPCon, HJT and BC technologies (market share, bifaciality, cost and shading notes; November 2024)
- SurgePV, TOPCon vs other solar technologies (typical efficiency, temperature coefficient and bifaciality ranges; publisher discloses a commercial relationship)