Highly efficient Cu(In,Ga)Se2 solar cells grown on flexible polymer films Adrian Chiril˘a1*(, Stephan Buecheler1, Fabian Pianezzi1, Patrick Bloesch1, Christina Gretener1, Alexander R. Uhl1, Carolin Fella1, Lukas Kranz1, Julian Perrenoud1, Sieghard Seyrling1, Rajneesh Verma1, Shiro Nishiwaki1, Yaroslav E. Romanyuk1, Gerhard Bilger2 and Ayodhya N. Tiwari1
Solar cells based on polycrystalline Cu(In,Ga)Se2 absorber layers have yielded the highest conversion efficiency among all thin-film technologies1–3, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies4. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.