Synchronous spectral management and UV tolerance in carbon-based perovskite solar cells by Eu3+ doped BaTiO3/TiO2 nanocomposite ETL

Down-conversion, a Stokes emission, is a solution for overcoming UV-driven deterioration and maximizing current collection in the perovskite solar cells. Down-conversion nanophosphor plays a crucial role in converting a single high-energy UV photon into multiple low-energy visible photons; thus, it aids the perovskite layer to absorb multiple photons, resulting in increased carrier generation. For the first time, Eu 3+ :BaTiO 3 /TiO 2 nanocomposite was used as the electron transport layer in the carbon electrode-based perovskite solar cells. This Eu 3+ :BaTiO 3 owns unique benefits possessed by the Lanthanide doping onto the perovskite oxide host matrix. The optimization of nanophosphor involved varying the concentrations of the Eu dopant (0, 1, 3, 5, 7 & 9 mol%). Based on the performance, 5 % Eu concentration was selected as the optimal version, corroborated by suitable material characterizations. On compositing this 5 mol% Eu 3+ :BaTiO 3 with TiO 2 in different wt% (0, 20, 40, 60, 80 and 100), the superior variant (40 %Eu-BTO-based-device) produced the highest efficiency (η) = 11.4 %, J sc = 22.28 mA/cm 2 and FF = 53.5 % among others. This champion device retained 83 % of its initial efficiency after 40 days under ambient conditions (relative humidity ∼50 %) and 72 % of its initial efficiency after 48 h under continuous UV illumination. The reproducibility and the cell performances were examined by adequate studies and the evidence supporting the results was discussed. This research demonstrated that the remarkable Eu-BTO/TiO 2 nanocomposite, used for electron transportation in the economical perovskite solar cell, enhanced device stability by reducing degradation caused by environmental moisture and UV irradiation. • For the first time, the rare-earth lanthanide (Eu)-doped perovskite oxide (BaTiO 3 ) is employed as a down-conversion nanophosphor in HTL-free C-PSCs. • The add-on novelty of this work lies in the selection of the electron transport material i.e, Eu 3+ :BaTiO 3 +TiO 2 nanocomposite and its economical device architecture, FTO/c-TiO 2 /Eu 3+ :BaTiO 3 +TiO 2 /CH 3 NH 3 PbI 3-x Cl x /Carbon, which is found reported nowhere. • The champion device attained an efficiency of 11.4 % with 53.5 % of FF, 955 mV of V oc and a P max of 2.85 mW. The highest current collection obtained with the optimized ETL nanocomposite is 22.28 mA/cm 2 , which is 81.9 % of the theoretical maximum. • This nanophosphor-embedded device exhibited excellent moisture stability by retaining 83 % of its initial efficiency after 40 days under ambient conditions (relative humidity ∼50 %). • In addition, it effectively maintained 72 % of its original efficiency after 48 h of continuous UV exposure by mitigating the thermalization losses, thereby promoting the photostability.