The perovskite device with a single TPBi ETL (Figure ) was fabricated using the above methods. However, 40 nm of TPBi was deposited replacing the 20 nm of TmPyPB. The TPBi EL device (Figure ) was fabricated using the same PEDOT: PSS deposition techniques and subsequently 40 nm of TPBi replaced the original TmPyPB/TPBi layer. No perovskite layer was deposited.