The franchise was founded in 1967 as one of the first expansion teams during the leagues 1967 NHL Expansion from six to twelve teams. The Penguins played in the Civic Arena (Pittsburgh), also known as The Igloo, from the time of their inception through the end of the 2009–10 season, when they moved to the PPG Paints Arena. The 1992–93 Pittsburgh Penguins season won the franchises first-ever Presidents Trophy for being the team with the most points at the end of the regular season. In addition to their eight division titles, they have qualified for six Stanley Cup Finals, winning the Stanley Cup five times – in 1990–91 NHL season, 1991–92 NHL season, 2008–09 NHL season, 2015–16 NHL season, and 2016–17 NHL season. Along with the Edmonton Oilers, the Penguins are tied for the most Cup championships among non-Original Six teams and sixth overall. With their Stanley Cup wins in 2016 and 2017, the Penguins became the first back-to-back champions in 19 years (since the 1997–98 Detroit Red Wings) and the first team to do so since the introduction of the NHL salary cap.
Answer this question: In which years did the Penguins win back-to-back championships?
n 1990–91 NHL season