Most mains powered Zigbee devices act as extenders in this sense.(they are usually referred to as “repeaters“ because you get more range because they can repeat the signal for other devices.)
For outdoor use, it is quite common to just put a outlet protectant box around an existing outlet and then use any inexpensive repeating smart plug you like. What country are you in? The device selection does vary. There are many different brands of these boxes, but typically you should be able to get them for less than €10. Just don’t get one that is metal or blue plastic as they tend to reduce signal. Other colors of plastic are usually fine.
Otherwise you have to look for a outdoor rated smart plug.
(The Hue outdoor motion sensor battery which was suggested won’t help: it’s a battery powered device and not a repeater. It should have the same range as your other Zigbee sensor and doesn’t repeat for other devices)
Do not try to use a hue bulb as a repeater: you will not be happy with the results.
FAQ: Are Smart Bulbs Repeaters? (Updated 2019: the new answer is yes, but may be inconsistent)