The disclosure relates to a door opener to open a door of a cassette with substrates, the opener having a first wall to engage with the cassette and having a first opening to transfer the door and the substrates and a second wall opposite the first wall and having a second opening to transfer substrates. The door opener may have a closure device to hold the door of the cassette and having first and second sides and moveable in a chamber formed between the first and second wall. The opener may have a first actuator to move the closure device in a first direction from a first closing position where the first side closes against the first wall to a second closing position where the second side closes against the second wall, and from the second closing position to a transport position in between the first and second closing positions.