GCL Highlights 4T Tandem Architecture For Next-Generation PV

As silicon solar cells approach their practical efficiency limits, tandem architectures are increasingly being explored as the next pathway for improving PV performance. The industry focus is also shifting toward higher efficiency. Modules now account for a smaller share of total system costs, while balance-of-system expenses continue to gain importance. Silicon PV is also nearing its theoretical efficiency ceiling, with the silicon Auger limit at 29.43% and laboratory silicon cell efficiencies already approaching 28%.

At the recent TaiyangNews Conference on Next-Generation PV Technologies, Bin Fan, Founder and CEO of GCL Optoelectronics, presented the company’s approach to perovskite-silicon tandem photovoltaics. He discussed the 4-terminal (4T) tandem architecture as a commercially scalable alternative to monolithic 2-terminal (2T) tandems. In his presentation titled Tandem at the Module Level: GCL’s Simplified Route to Next-Generation PV, Fan focused on the manufacturing flexibility, field-performance advantages, and material-selection freedom associated with the 4T approach.

A major focus of the presentation was GCL’s preference for 4T tandem architecture over monolithic 2T designs. In the 2T approach, the perovskite layer is deposited directly on the silicon wafer, and both sub-cells are electrically connected in series. This makes the total current dependent on the weaker sub-cell. In the 4T route, the perovskite module is separately fabricated on glass and later stacked with the silicon module. Both sub-cells remain electrically independent and operate at their own maximum power points.

Manufacturing simplicity formed one of the central arguments for the 4T approach. Monolithic 2T tandems require perovskite deposition directly on textured silicon wafers, making large-area uniform coating more challenging. Different silicon technologies, such as TOPCon, HJT, and IBC, also require separate process integration approaches. In contrast, the 4T route processes the perovskite layer on flat glass substrates and integrates the stack at the module level. According to Fan, the same perovskite top module can therefore be combined with TOPCon, HJT, IBC, or PERC bottom cells without redesigning the perovskite process.

The company also linked the 4T structure to improved field performance. Spectral variation, changing air mass, cloud cover, and temperature shifts continuously alter the current-matching point in 2T tandems. GCL estimated that these mismatch effects could translate into around 7% annual energy-yield loss in 2T systems. In the 4T architecture, each sub-cell operates with independent MPPT control and DC-DC optimization, enabling real-time voltage matching and potentially delivering a 2% to 4% energy-yield advantage.

Another major discussion point was the operating window of both tandem architectures. According to GCL's calculations, the 2T structure reaches peak efficiency only near an optimal bandgap of ~1.73 eV, beyond which efficiency rapidly declines due to current mismatch. The efficiency window above 40% spans only ~0.22 eV for 2T tandems, compared to ~0.95 eV for 4T architectures.

GCL linked this wider operating window to greater flexibility in perovskite material selection. The wider bandgap tolerance allows researchers to optimize perovskite materials simultaneously for efficiency, stability, and processability. The company described the 4T structure as an ‘open platform’ capable of accommodating future perovskite compositions without redesigning the full tandem stack.

Fan’s presentation also focused heavily on reliability and long-term stability. He noted that 2T tandems are generally constrained to mixed-halide perovskites in the 1.7-1.8 eV range, where light-induced halide segregation remains a challenge. The 4T route instead uses single-halide perovskites around 1.53 eV, which the company described as more stable under thermal and light exposure. GCL added that its tandem modules have already received IEC 61215 certification from TÜV Rheinland, including extended 3× IEC testing.

He also highlighted silver consumption and metallization as differentiating factors. 2T tandem structures rely on low-temperature silver paste for front-side metallization, increasing both silver consumption and degradation risks. Fan pointed to the potential formation of insulating AgI compounds through silver-iodide reactions in perovskite structures. GCL’s 4T architecture instead uses transparent conductive oxide (TCO) front electrodes, eliminating direct silver-perovskite contact.

Fan also attempted to address concerns around system integration. He explained that the 4T architecture can still provide a standard 2-terminal module output via voltage matching and DC-DC optimization, allowing compatibility with existing inverter infrastructure and BOS components.

Alongside the technical discussion, Fan shared updates on GCL’s tandem manufacturing roadmap. The company reported a 29.51% tandem module efficiency on a 2,048 cm² module and 27.06% efficiency on a 1.71 m² near-commercial-size module. It now targets 27% efficiency on a full-size 2.76 m² tandem module measuring 2,400 mm × 1,150 mm.

GCL has built a 500 MW tandem-module production line and aims to produce and ship around 100 MW of tandem products in 2026. The company’s longer-term target is to expand tandem-module manufacturing capacity to around 2 GW.

The TaiyangNews Cell & Module Technology Trends 2026 report also covered GCL’s views on energy consumption and production scale in polysilicon manufacturing.