Transparent Luminescent down-conversion coating for improved performance and enhanced stability of carbon-based perovskite solar cells

Methylammonium lead halide-based perovskite solar cells (PSCs) perform superior photovoltaic performance, nevertheless, demonstrate limited light utilization and instability within the ultraviolet (UV) range. Lanthanidebased down-conversion (DC) materials can mitigate the photoinduced deterioration by resolving spectrum mismatched losses. Particularly, lanthanide complexes possess a broad UV absorbing region thus can convert absorbed UV light to visible or near-infrared light, exhibiting large pseudo-Stoke's shift while they could allow spectrum responsiveness of the PSCs in the UV. Therefore, the DC material may enhance the photovoltaic performance by converting high-energy photons to low-energy photons whilst may also perform as UV shielding material, and finally may both develop PSCs' efficiency and stability. Herein, a novel transparent luminescent down-converting layer (LDC) based on a highly emitting Europium complex in a siloxane matrix was used as an external coating to PSCs with the purpose of improving the solar cells' performance extending their response in the UV region while improving cells' photostability. The conducted studies indicated that the LDC coating may additionally serve as an anti-reflective and UV-shielding layer simultaneously, resulting in better light-harvesting ability of the perovskite. As a result, short circuit current (Jsc) amplification by the presence of LDC re-emitting the absorbed UV light to the visible and the best carbon-based perovskite solar cell (C-PSC) revealed a 16.13 % overall performance in comparison to the 15.38 % obtained for the control device. Furthermore, photostability tests demonstrated that the unencapsulated LDC-modified devices prepared under ambient conditions retained 75 % of their initial PCE after 8 h under artificial solar light illumination whereas the control devices remained at 40 % at the same conditions. These findings suggest that the LDC layer decreases the UV degradation for PCEs, resulting in PCE and stability enhancement.