Search

Abstract: Recently, the influence of molecular weight (Mn) on the performance of polymer solar cells (PSCs) is widely investigated. However, the dependence of optimal thickness of active layer for PSCs on Mn is not reported yet, which is vital to the solution printing technology. In this work, the effect of Mn on the efficiency and especially optimal thickness of the active layer for PBTIBDTT‐S‐based PSCs is systematically studied. The device efficiency improves significantly as the Mn increases from 12 to 38 kDa, and a remarkable efficiency of 10.1% is achieved, which is among the top efficiencies of wide‐bandgap polymer:fullerene PSCs. Furthermore, the optimal thickness of the active layer is also greatly increased from 62 to 210 nm with increased Mn. Therefore, a device employing a thick (>200 nm) active layer with power conversion efficiency exceeding 10% is achieved by manipulating Mn. This exciting result is attributed to both the improved crystallinity, thus hole mobility, and preferable polymer orientation, thus morphology of active layer. These findings, for the first time, highlight the significant impact of Mn on the optimal thickness of active layer for PSCs and provide a facile way to further improve the performance of PSCs employing a thick active layer. [ABSTRACT FROM AUTHOR]

In this work, we synthesized a low bandgap polymer polysilole(-2,6-diyl-alt-5-octylthieno[3,4- c]pyrrole-4,6-dione) (PDTSTPD) with different molecular weights ( Mn). The devices based on PDTSTPD/PC71BM composite are prepared and the dependence of power conversion efficiency (PCE) of the devices on the Mn of conjugated polymers is addressed. We found the hole mobility of PDTSTPD is dependent on the Mn of the polymer, which should be the main reason contributing to the drastic difference of device performance, i.e. the PCE of the device using 10 kDa polymer is only 0.52%, in contrast to 2.3% for 24 kDa polymer device. This PCE data is then further improved to 5.0% via using 1,8-diiodoctane as processing additive to achieve an optimized morphology for the photoactive layer with an appropriate length-scale of phase separation for both exciton dissociation and charge transportation. [ABSTRACT FROM AUTHOR]