Ultrathin Flexible Transparent Composite Electrode via Semi-embedding Silver Nanowires in a Colorless Polyimide for High-Performance Ultraflexible Organic Solar Cells

Ultraflexible organic solar cells (OSCs) with both high power conversion efficiency (PCE) and good mechanical robustness are still challenging, in which flexible transparent composite electrodes (FTCEs, substrate-cum-electrodes) play critical roles. Here, an ultrathin FTCE (similar to 9 mu m) via semi-embedding a silver nanowire electrode in a colorless polyimide (CPI) substrate was developed, which simultaneously possessed outstanding performance such as low square resistance (R-sq similar to 12.7 Omega sq(-1)), high optical transmittance (T-550 similar to 86.3%), smooth surface (root-mean-square similar to 0.32 nm), and excellent thermal, mechanical, and solution producing stability. Prior to the FTCE fabrication, four CPI samples with the number-average molecular weight ranging from 35.9 to 177.5 kDa were prepared and their optical, mechanical, and thermal properties were studied in detail. Moreover, the effect of the molecular weight on the minimum thickness that can withstand the following solution production of ultraflexible OSCs was investigated, which revealed that the molecular weight of CPI here should be above 81.4 kDa. Based on the FTCE, an ultraflexible OSC with a high PCE value of 14.37% and outstanding mechanical robustness was constructed, in which the PCE could still maintain above 96% of its initial value after 1000 bending cycles at a bending radius of 0.5 mm.

Automated summary

This study developed an ultra-thin FTCE (flexible transparent composite electrode) by semi-embedding a silver nanowire electrode in a colorless polyimide substrate, achieving high performance and good mechanical stability. The molecular weight of CPI needs to be above 81.4 kDa to prepare ultraflexible OSCs with good performance.