A heterojunction cell, also called SHJ or HJT, is a crystalline silicon cell structure. Its junction is formed by amorphous silicon (a-Si:H) passivation layers on a crystalline silicon wafer. Along with TOPCon, it is one of the newer cell technologies whose long-term reliability is still being studied. Fielded SHJ modules degrade at about the same yearly rate as conventional silicon modules. The loss shows up mainly as lower voltage, not lower current. This voltage loss is linked to weathering-related defects near the boundary between the wafer and the a-Si:H layer, which raise recombination. SHJ cells can lose Voc under UV light because the front passivation weakens. Moving to rear-emitter designs historically solved this, and light soaking may recover UV losses. A possible new potential-induced degradation mechanism has been found for SHJ modules, but no affected modules have been seen in the field yet. Heterojunction modules have low temperature coefficients, so they are a good choice for hot sites.
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subclass_ofc1 drafted · lead Crystalline silicon PV
HJT is listed among current c-Si cell structures together with TOPCon, PERT and PERC.
sec=2.6.3 h=447bcab4e244review note: support check: partial - Passages list HJT among current c-Si cell structures, but "kind of crystalline silicon PV" is only implied (c-Si/a-Si:H, 'current c-Si cell structures').
related_toc2 verified · fact TOPCon cell
Both are newer cell designs whose reliability, including UV-induced and potential-induced degradation, is assessed side by side.
sec=2.6.3 h=447bcab4e244sec=h15 h=1e249684bb32verified by: review-workflowverified on: 2026-10-24
Field degradation of SHJ modules was compared with PERC; PERC losses come mainly from Isc, while SHJ losses come mainly from voltage.
sec=2.6.3 h=447bcab4e244c4 drafted · lead UV-induced degradation proposed
In SHJ cells, UV exposure lowers Voc because the front passivating layers partly lose their properties. Light soaking may recover the loss.
sec=2.6.3 h=447bcab4e244sec=h15 h=1e249684bb32c5 drafted · lead Potential Induced Degradation (PID)
A new possible PID mechanism has been identified for SHJ modules, but no field modules affected by it have been found yet.
sec=h15 h=1e249684bb32fig=69 h=ac9e8219941fc6 drafted · lead Temperature coefficient
Heterojunction modules are named as having low temperature coefficients, which makes them suitable for hot sites.
sec=6.5 h=778f245ec3d5degradation_ratec7 drafted · lead nominal -0.51 PERCENT-PER-YR
Conditions: Observed degradation rate of fielded SHJ modules (Jordan et al.), on par with conventional Si cell technologies
sec=2.6.3 h=447bcab4e244typical_power_lossc8 drafted · lead 1–2.5 PERCENT
Conditions: Power degradation of 2 SHJ module types after an accelerated UV test dose of 60 kWh/m² under short-circuit conditions
sec=2.6.3 h=447bcab4e244related_to c2