Where photons should be regulated: Optically first charge-transport layers for bifacial perovskite photovoltaics

Bifacial perovskite photovoltaics offer strong potential for multidirectional light harvesting, yet their commercial deployment is constrained by parasitic optical loss and ultraviolet (UV)-driven chemical degradation. To suppress UV-initiated degradation at its origin, we introduce a photon-energy regulation strategy integrated directly into the optically first charge-transport layers (OF-CTLs) on both sides of the device. Through rare-earth spectral engineering, europium functions as a multifunctional dopant, enabling UV-to-visible down-conversion while preserving and improving bidirectional charge transport. Guided by optical transfer-matrix modeling, this dual-side architecture reshapes the internal optical field, suppresses UV-induced defect formation, and enhances visible-photon utilization. Implemented in bifacial perovskite modules, this strategy delivers a certified front-side efficiency of 18.48% in 30 × 30 cm 2 submodules, together with exceptional UV resilience and sustained outdoor operational stability. This work repurposes native transport layers as active OF-CTLs for durable, high-efficiency optoelectronics.