Surface modified fullerene electron transport layers for stable and reproducible flexible perovskite solar cells

We report flexible planar perovskite solar cells with robust electron-transport layers (ETLs) processed at low temperature. A poly(allylamine) (PAA; 0.08 wt%) solution was deposited on a C-60 layer and heated at 150 degrees C for 60 s, resulting in the formation of an insoluble robust C-60-PAA electron-transport layer (ETL) on the flexible substrate. The flexible planar perovskite solar cell with the C-60-PAA ETL exhibited excellent properties with 83% efficiency retention (eta= 15.2% without hysteresis) after 600 cycles of bending. This performance is superior to that of the flexible device with a C-60 ETL fabricated without the use of PAA (65% efficiency retention; eta = 9.8% with some hysteresis).