Thermal-annealing-free inverted polymer solar cells using ZnO/Cs2CO3 bilayer as electron-selective layer

Abstract

We report on thermal-annealing-free inverted polymer solar cells using ZnO nanoparticles (NPs)/Cs2CO3 bilayer as an electron-selective layer (ESL) and the blend of poly(3-hexylthiophene) (P3HT): phenyl C61-butryricacid methyl ester(PCBM) as an active light-absorbing layer. These layers were deposited via solution process without additional thermal treatment. The cell gave power conversion efficiency (PCE) of 3.81%, which was higher by about 40% or 80% than that of the cell with single ZnO NPs or Cs2CO3 ESL, respectively. This improved performance could be attributed to the bilayer-structure ESL, whose electron-extraction and leakage-current-suppression abilities were enhanced due to its modified energy level and improved surface morphology. PCE of this device remained 92% of its original value after storage of the as-fabricated device in a N2-filled glove box for 80 day. Furthermore, when the blend of poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)]: [6,6]-phenyl C71 butyric acid methyl ester replaced P3HT:PCBM as the active layer, higher PCE of 6.45% was achieved in the corresponding cell.