Struggling Posh swooped to the points with alarming ease courtesy of goals from Lee Tomlin, Tommy Rowe and Dwight Gayle - but Solbakken refused to point the finger at his players.
He said: "Rather than pointing fingers at the players I will take the blame myself. Sometimes when one, two or three players have an off day you can explain it.
"But I think I saw seven, eight or nine players have a really bad day with the ball. Defensively we were vulnerable to counter-attacks and I didn't see any belief after it was 2-0.
"We had the ball all the time but we didn't open them up in the second half so I have to look at myself in the mirror and see what I have done wrongly in the preparation of the tactics."
He added: "It was a hard blow for us and it will be hard to retain mental strength before Saturday (against Ipswich). Mentally we were weak. It should not be a catastrophe going 1-0 down against Peterborough with 75 minutes left.
"We didn't look lively and that disturbs me. The body language was like 'ok we will go out and steal the points maybe using as less power or strength as possible'.
"That doesn't work in this division and that really annoys me. It is my responsibility. That I can say. When so many players don't seem to be up for it I have to take the responsibility and that is how it is in this game."