How to Read Solar Cell Technology Routes — PERC, TOPCon, HJT and Back Contact: What Each Name Means, Which Datasheet Numbers Change, Which Degradation Tests Apply, and What China's Norms Require

Short answer. The route names on a module datasheet describe how the cell's surfaces are passivated and contacted, and they move three things a buyer can check: the average-efficiency conditions MIIT's 2024 norms set for enterprises by cell type, the bifaciality and temperature-coefficient ranges typical of the architecture, and the degradation mechanisms the module should have been tested against. The industry has shifted from p-type PERC to n-type routes — IEA PVPS puts n-type at 70% of global production — and the IEA and NREL describe TOPCon, heterojunction and back contact as the routes expected to deliver higher efficiency. This guide explains the vocabulary from those public sources and lists the questions to ask; it does not say which route is best and rates no supplier.

What the names mean

The IEA's 2022 supply-chain report traces the sequence: multicrystalline BSF cells were gradually replaced by more efficient PERC cells from 2015, with monocrystalline wafers and process improvements making PERC the dominant technology; greater market shares were anticipated for heterojunction (HJT), TOPCon and back-contact cells, with modules using such cells reaching 22% efficiency in real-life conditions; and mass manufacturing of silicon–perovskite tandems was under consideration, with potential cell efficiencies above 30%. NREL's 2020 module-technology benchmark describes PERC as having displaced full-area Al-BSF owing to a 1.0–1.5% absolute module-area efficiency gain, and names interdigitated back contact (IBC), PERT/PERL and silicon heterojunction (SHJ) as architectures that could deliver higher efficiencies; PERC is shown monofacial, though bifacial configurations are also used.

In that vocabulary, the three routes in this guide's title sit as follows: TOPCon is a passivated-contact design on an n-type wafer (NREL's p-type passivated-contact and PERT/PERL categories are its neighbours); HJT is NREL's SHJ; and "BC" is back contact, of which IBC is the monocrystalline form. The IEA notes that cell processing differs by route — at least 8 process steps for heterojunction cells and 11 for TOPCon cells — including texturing, cleaning, doping, etching and printing silver-paste contacts. Step count is a manufacturing fact, not a quality ranking.

Which datasheet numbers change with the route

NREL's 2020 benchmark Table 1 gives expert-workshop values of bifaciality factor and power temperature coefficient by architecture: PERC 0.65–0.80 and −0.25 to −0.40 %/°C; PERT/PERL 0.85–0.90 and −0.40 to −0.45 %/°C; SHJ 0.80–0.95 and −0.25 to −0.30 %/°C; back contact 0.40–0.50 and −0.25 to −0.30 %/°C (Al-BSF −0.35 to −0.40 %/°C, no bifaciality); the bifaciality factor is measured indoors as rear-side versus front-side generation under the same illumination and temperature. These are 2020 reference ranges, not current product values, and a datasheet value outside them is not wrong — but it should be explained by the supplier's own measurements. Bifacial I-V measurement has its own procedure: IEC TS 60904-1-2:2019 describes the measurement of current-voltage characteristics of bifacial PV devices (cells, sub-assemblies or modules) in natural or simulated sunlight, as additional requirements to standard I-V measurement.

Two more route-dependent facts from NREL's 2020 benchmark: all n-type architectures together were roughly 11 GW (10% of cell production) in 2019 per ITRPV, n-type wafers had become available at prices within 5–10% of p-type monocrystalline wafers, all n-type architectures shown have fully licensable intellectual property, and, except for IBC, all have multiple turnkey equipment vendors at scales from 50 MW to multiple gigawatts. Back-contact growth may be driven by higher efficiencies and smaller temperature coefficients but hindered by higher manufacturing costs from process complexity, and an all-screen-printed IBC cell does not clearly outperform passivated contacts on p-type monocrystalline or SHJ cells.

The shift has since happened. The IEA PVPS Trends in Photovoltaic Applications 2025 report page states that module efficiencies continue to improve, with n-type technologies now representing 70% of global production, and that bifacial modules make up over 75% of production. NREL's Winter 2025 Solar Industry Update reports, citing Clean Energy Associates, slowing efficiency improvements due to R&D cuts and delayed equipment investment under reduced margins and growing patent litigation related to new technologies such as TOPCon, and the view that litigation may keep PERC dominant in the United States with efficiencies below 24% for the foreseeable future. CNWattHub editorial method: for an n-type route, ask the supplier to state its licensing position for the cell architecture in the destination market; NREL's 2020 note that the n-type architectures' intellectual property is licensable is not a statement that any particular maker holds a licence.

What China's norms require by route

MIIT's 2024 PV Manufacturing Industry Norms (公告2024年第33号) set minimum average cell efficiencies for existing enterprises of 21.4% (multicrystalline), 23.2% (p-type mono) and 25% (n-type mono), and for new or expanded projects 21.7%, 23.7% and 26% (bifacial cells by front-side efficiency); module minimums for existing enterprises are 19.4%, 21.2% and 22.3%. The Norms also set wafer minority-carrier-lifetime minimums that distinguish heterojunction: for existing enterprises n-type mono wafers ≥800 μs (carbon/oxygen <1 ppma/12 ppma) but n-type wafers for heterojunction cells ≥500 μs (carbon/oxygen <1 ppma/14 ppma); for new or expanded projects ≥1,000 μs and ≥700 μs respectively. So the Norms do not name TOPCon or BC; they distinguish p-type from n-type and single out HJT wafers. These are average photoelectric-conversion-efficiency conditions for the enterprise categories the Norms cover (existing enterprises; new or expanded projects). Compare a supplier's average cell efficiency with the figure for its enterprise category only when checking whether that enterprise meets the Norms. The indicators cannot on their own verify an "N-type" label, and they are not a mandatory minimum efficiency for every product.

Policy direction is explicit. The NEA-led 2025 Guiding Opinions on energy equipment (国能发科技〔2025〕78号) call for breakthroughs in high-efficiency silicon–perovskite tandem, heterojunction and back-contact module technologies and in high-efficiency PV systems and high-voltage string inverters.

Which degradation tests apply

Route changes the degradation questions. IEC TS 63342:2022 (published 20 July 2022) assesses light- and elevated-temperature-induced degradation (LETID) by current injection at higher temperatures; it does not address boron–oxygen or iron–boron degradation, and can reveal sensitivity to LETID but does not provide an exact measure of field degradation. IEC TS 62804-1:2025 defines procedures to evaluate crystalline-silicon module durability under short-term high-voltage stress, primarily potential-induced degradation (PID), with dark tests for PID-shunting and UV-including tests for PID-polarisation plus a recovery test. Both sit on top of design qualification: IEC 61215-2:2021 lays down design-qualification requirements for terrestrial PV modules for long-term open-air operation, applying to all flat-plate module materials including crystalline silicon and thin film, with a test sequence intended to determine electrical characteristics and show the module can withstand prolonged outdoor exposure; the 2021 edition added cyclic (dynamic) mechanical load testing (MQT 20).

CNWattHub editorial method: ask for the IEC 61215 report plus, by route, the LETID and PID reports and the bifacial I-V report, and check that the sample tested is the cell and module type offered.

Reading a record claim

Suppliers cite "record" efficiencies. NLR (NREL) maintains the Best Research-Cell Efficiency Chart of the highest confirmed research-cell efficiencies by technology since 1976; entries must be confirmed by independent recognised test laboratories (e.g. NLR, AIST, JRC-ESTI, Fraunhofer ISE) and reported with respect to standard test or reporting conditions. A research-cell record is a laboratory cell measured under standard conditions; it is not a production-module efficiency, and the chart's values are not quoted here.

Checklist by route

Scope limits

Standards are described from webstore abstracts; the IEA, NREL and IEA PVPS documents are quoted for their descriptions and summary figures only. No 2024–2025 share by individual route was found in an official source. The NREL 2020 ranges are presented as a 2020 reference. No supplier, product, price or efficiency claim is compared or recommended.