PSG's goal was scored after Araujo received a red card in the 29th minute. PSG played quite well in that match but I think the red card that Araujo received had a significant impact on Barcelona's game. They cannot implement tactics and games as planned. And PSG was able to take advantage of that moment very well.
PSG play very quite in that their game against Barcelona the game really surprised so many peoples, because nobody expect that turn out from the PSG due how the Barcelona performance is thur far this season, but since their able to hold their consistent well that's why they definitely lose to Barcelona. Honestly the red card that Barcelona received in 29minutes is part of what weak their performance the red card really affected them if not i don't think PSG can able to beat them. As it stands now PSG have directly advance to the semi-final let us be watching and what can actually happen in the semi final against Dortmund, since although that they're also a strong team this season.
Dortmund are not a bad team, but I think they are on a bad run in their league. You are right that teams from the Bundesliga have their own motivation in the Champions league but I think Dortmund is one level below PSG. This is different from Munich, which can be said to be on an equal level with Madrid, although I still favor Real Madrid to become champions.
Seriously speaking Dortmund are not a bad team if we can observed their last match against Leverkusen in the Bundesliga league they really perform in that match, and that's what is given some hope that Dortmund can put much effort and try their possible best and make sure they dominate the semi-final so that they can advance to final stage with full confidence.