The electric field inside a closed conducting shell (electrostatic shielding/Faraday cage principle) is zero when only external charges are present. No citation is needed as this is a fundamental, standard result of classical electrostatics.
The claim is a direct textbook principle of electrostatics (electrostatic shielding/Faraday cage effect), making it common knowledge. None of the retrieved papers specifically test or discuss this elementary shielding property for hollow conducting shells under external charges; instead, they cover unrelated topics such as 3D printed sensors, triboelectric nanogenerators, and superconductor E-J characteristics.