Achieving an Efficiency Exceeding 10% for Fullerene‐based Polymer Solar Cells Employing a Thick Active Layer via Tuning Molecular Weight

Abstract

Recently, the influence of molecular weight (M n ) on the performance of polymer solar cells (PSCs) is widely investigated. However, the dependence of optimal thickness of active layer for PSCs on M n is not reported yet, which is vital to the solution printing technology. In this work, the effect of M n 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 M n 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 M n . Therefore, a device employing a thick (>200 nm) active layer with power conversion efficiency exceeding 10% is achieved by manipulating M n . 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 M n 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.

High‐Performance Additive‐/Post‐Treatment‐Free Nonfullerene Polymer Solar Cells via Tuning Molecular Weight of Conjugated Polymers

“…The finer fibrillar structures are beneficial for the charge separation and transport and thus contribute to the enhanced hole mobility as well as PCE. This result was significantly different from the phenomena present in the PBTIBDTT‐S:PC 71 BM blend films in which the widths and lengths of the fibrils were obviously increased as the M n going from 12 to 38 kD . This discrepancy might result from the different interaction between the donor and acceptors in the fullerene and nonfullerene systems due to the different molecular structure.…”

“…It is interesting to find that all these devices delivered their optimal PCEs with an active layer around 80 nm without any additives and post‐treatments. This variation trend of the optimal active layer thickness is significantly different from that in the fullerene system, in which the optimal active layer thickness gradually enhanced with the increase of M n . The 12, 23, 31, and 38 kDa PBTIBDTT‐S‐based device showed a continuously decreased optimal donor:acceptor ratio of 1:0.4, 1:0.67, 1:1, and 1:1, respectively.…”

Fluorination Triggered New Small Molecule Donor Materials for Efficient As‐Cast Organic Solar Cells

“…It is noteworthy that the visible blend morphology of DI3T‐2F:PC 71 BM became smooth with optimal phase separation. We speculate that, in contrast to DI3T:PC 71 BM, the smaller domain size with homogenous blend morphology of DI3T‐2F:PC 71 BM offers greater efficiencies for charge generation and transport, efficiencies that are beneficial for higher device performance …”

“…Compared to polymers, small molecules (SM) have been investigated as alternative candidates to polymeric counterparts as donor components, due to their defined chemical structures, easier purification, and less batch‐to‐batch variation synthesis . As a result, the performance of solution‐processed BHJ‐OSCs based on SM donor:fullerene derivatives (SM‐OSCs) has been dramatically improved to over 11%, which is approaching the performance obtained for polymer solar cells …”

Asymmetric Wide‐Bandgap Polymers Simultaneously Improve the Open‐Circuit Voltage and Short‐Circuit Current for Organic Photovoltaics

“…Therefore, the optimized phase separation morphology of active films by TA treatment supports the increase in J SC of the photovoltaic devices. The space charge‐limited current method with the hole‐only device (ITO/PEDOT:PSS/active layer/MoO 3 /Ag) and electron‐only device (ITO/ZnO/active layer/Al) . Detailed information is shown in Figure S14 and Table S1, Supporting Information.…”