At a recent TaiyangNews conference, Menglei Xu, R&D Director at JinkoSolar, presented advancements in this field, including a perovskite-TOPCon tandem cell achieving a conversion efficiency of 34.76%. This milestone was enabled by the use of commercial TOPCon cells with efficiencies above 27% and open-circuit voltages (Voc) exceeding 748 mV, underscoring the importance of high Voc in two-terminal (2T) tandem configurations.
JinkoSolar’s approach involves depositing the perovskite layers on the rear side of the TOPCon cell, effectively flipping the structure to form the tandem device. Since the rear surface is initially planar, it must first be textured to form pyramidal features approximately 0.6-0.7 µm in size to enhance light management. Using a configuration with n-type poly-silicon fingers on the front and a full-area p-type poly layer on the rear, the team achieved an efficiency of 32.73%. However, parasitic absorption in the rear p-poly layer limited the short-circuit current density (Jsc) to 20.4 mA/cm², highlighting a key area for further optimization.
On the perovskite side, several material and interface improvements contributed to performance gains. The introduction of a self-assembled monolayer (SAM) on the NiOx hole transport layer improved hole selectivity and enabled a tandem Voc of 2.01 V. Stability was addressed through additive engineering in the perovskite precursor, including the use of thioacetylacetamide hydrochloride (TAACl), which improved bromine distribution and reduced phase segregation during operation.
Additional additives such as 2-mercaptobenzothiazole were explored to improve crystallization dynamics. This is particularly important in tandem devices, where perovskite films crystallize more rapidly than in single-junction cells, often leading to poorer film quality. With these optimizations, a tandem device achieved 32.76% efficiency while retaining 91% of its initial performance after 1,700 hours of continuous operation.
Further improvements were demonstrated using potassium salt additives to enhance perovskite layer uniformity on textured surfaces. This resulted in a device efficiency of 33.65%, which maintained over 80% of its performance after 1,000 hours of maximum power point tracking at 85°C.
Xu emphasized that while multiple tandem configurations - including 2T, 3T, and 4T - remain promising, the key challenge lies in scaling these technologies for commercial deployment. He projected that a pilot production line with hundreds of megawatts capacity could be operational within approximately three years, followed by gigawatt-scale manufacturing within four to five years.
