Interfacial Engineering for High Performance Inverted Polymer Solar Cells

Bulk heterojunction (BHJ) polymer solar cells (PSCs) that can be fabricated by solution processing techniques are under intense investigation in both academic and industrial sectors because of their potential to enable mass production of flexible and cost-effective alternative of silicon-based solar cells. A combination of novel polymer development, nanoscale morphology control and processing optimization has led to over 9% of power conversion efficiencies (PCEs) for BHJ PSCs with a conventional device structure. Attempts to develop PSCs with an inverted device structure as required for achieving high PECs and good stability have, however, met with limited success. Here, we report interfacial engineering for high performance inverted polymer solar cells. Our review include: (1) solution-processed zinc oxide (ZnO) thin film as an electron extraction layer for inverted polymer solar cells. Operated at room temperature, no obviously degradation was observed from the PSCs with ZnO layer after continuously illuminating the devices for 4 hours. However, a significantly degradation was observed from the PSCs without ZnO buffer layer after illuminating the devices only for 1 hour. Furthermore, PSCs with ZnO buffer layer also show very good shelf stability; only 10 % degradation observed in PCEs after 6 months; (2) a high PCE of 8.4% under AM1.5G irradiation was achieved for BHJ PSCs with an inverted device structure. This high efficiency was obtained through interfacial engineering of solution-processed electron extraction layer, ZnO, leading to facilitated electron transport and suppressed bimolecular recombination; (3) Further study of the effect on a novel water/alcohol-soluble neutral fullerene derivative (PC60BM-G2 ) layer on the device performance of the inverted PSCs is investigated. An over 30% enhancement in PCE was observed from the inverted PSCs with PC60BM-G2 layer to reengineer the surface of the ZnO EEL, when compared with those without PC60BM-G2 layers. All these results provided an important progress for solution-processed PSCs, and demonstrate that PSCs with an inverted device structure are comparable to PSCs with the conventional device structure