What is a quantum cryptography protocol that ensures the maximum distance in the case of a strictly single-photon source?

The distance of secret key distribution in the case of a strictly single-photon source has been analyzed for the BB84 protocol and phase time coding (the PTC protocol) protocols. It has been shown that the distance of secret key distribution ensured by the PTC protocol is almost 100 km longer than that by the BB84 protocol (the other parameters of the system being the same).