LAUSR

In the last three years, polymer solar cells (PSCs) based on ntype organic semiconductor (n-OS) acceptor have become the focus of attention and made great progress. In 2017, the power conversion efficiencies (PCEs) have been boosted to ~13% for PSCs with single-junction and ~14% for PSCs with double-junctions. However, the optimized active layer thickness and device area of the high efficiency PSCs are usually limited to ~100 nm and ~0.2 cm respectively, which makes the large area fabrication of PSCs very difficult. Recently, Prof. Zhang (in Prof. Li’s research team) [1,2] at Soochow University broke the above restrictions and made an important progress in high efficiency PSCs with thick active layer and large device area. In early 2014, Zhang et al. [3] first introduced fluorine atom into 2D-conjuaged thienyl benzodithiophene (BDTT-2F) to improve photovoltaic properties of polymers. And then, the wide bandgap polymer PM6 [4] with high absorption coefficient, low energy level and strong crystallinity, based on BDTT-2F as donor unit and benzodithiophene-4,8-dione as acceptor unit, was developed and achieved a PCE of 9.2% in PSCs based on PC71BM as acceptor. Recently, the nonfullerene (NF)-PSCs based on PM6 as donor have obtained excellent device performance by matching the n-OS acceptor IDIC. The PM6:IDIC-based PSCs without extra treatments show a high PCE of 11.9%, which is the record value for the as-cast PSCs reported to date. Moreover, the PCEs (over 11%) are insensitive to the active layer thickness (≈95–255 nm) and device area (0.20–0.81 cm). Besides, the PM6:IDIC-based flexible PSCs with a large device area of 1.25 cm also exhibit a high PCE of 6.54%. Very recently, by changing the matched n-OS acceptors from IDIC to tetrafluorinated IT-4F, the PCE of the PSCs based on PM6 was promoted to 13.5% due to the synergistic effect of fluorination on both donor and acceptor materials [2], which is among the highest values reported for PSCs to date. Furthermore, a PCE of 12.2% was remained in PSCs with a thick active layer up to 285 nm, and a PCE of 11.4% was also obtained in PSCs with a large device area of 1 cm (Figure 1). In addition, the devices also showed good storage, thermal and illumination stabilities with respect to the efficiency. The device performances are insensitive to the active layer thickness and device area, which should be benefitted from the high crystallinity and appropriate ag-