Abstract:
Electron selective intermediate layers are crucial for both efficiency and stability of the inverted polymer solar cells (IPSCs). In this paper, an established low-temperature (<130°C) recipe to fabricate nano zinc oxide (ZnO) layers (L-ZnO) exhibited typical values of power conversion efficiency (PCE∼ 3.3%) with the standard P3HT:PC61BM blend. However, PCEs showed further improvement up to ∼24% (∼ 4.08%) when
these layers were annealed at 300°C (H-ZnO). This annealing step can be bypassed by adopting a slightly different chemistry using Nafion as a modifier (NM-ZnO). I-PSCs fabricated with NM-ZnO showed nearly 40% increase in the PCE (∼4.62%) with PEDOT:PSS hole transport layers (HTL) that matches the so far highest recorded value for such a system. For the low-bandgap polymer blend PBDTT-FTTE:PC71BM, a peak efficiency of ∼6.77% was obtained compared to ∼5.34% with L-ZnO (∼28% increase). Our experiments revealed that these enhancements were due to a combination of benefits obtained from Nafion modification such as favourable positioning of work function (WF), high band gap (Eg) and better transport characteristics through the layer interfaces.
