Ternary Blend Organic Solar Cells Incorporating Ductile Conjugated Polymers with Conjugation Break Spacers

Abstract

A broad family of ductile semirandom donor− acceptor (D−A) copolymers with 8-carbon alkyl conjugation break spacer (CBS) units were incorporated into ternary blend organic solar cells in order to determine their impact on the electrical metrics of solar cell performance. The goal of this study was to elucidate potential co-optimization strategies for photovoltaic and mechanical properties in organic solar cells. The ternary blended active layers were based on two polymer donors and the acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PC 61 BM). In all cases, the majority polymer donor component was the previously reported fully conjugated semirandom polymer P3HTT-ehDPP-10%, comprised of 80% 3-hexylthiophene, 10% diketopyrrolopyrrole (DPP) with 2-ethylhexyl (eh) side chains, and 10% thiophene. As the second donor, three different classes of CBS polymers were used, where the spacer length was kept constant at 8 methylene units. The mechanical properties of these polymers are quite notable with moduli as low as 8.54 MPa and fracture strains as high as 432%. However, it was found that as ductility increased, hole mobility decreased. In this study, we observed that the hole mobilities of the ternary active layers generally increased upon increasing the content of the CBS polymer up to 15% of the overall donor fraction. The higher carrier mobilities likely contribute to the higher J SC observed in many of the ternary devices. The as-cast ternary solar cells made in ambient environment without any pre/post treatment gave strong performance up to 25% of CBS polymer loading. This work demonstrates that introducing highly stretchable CBS polymers with poor charge mobility does not adversely affect solar cell performance, offering insights into the development of ternary strategies for flexible/stretchable organic solar cells.

Sequentially Fluorinated Polythiophene Donors for High‐Performance Organic Solar Cells with 16.4% Efficiency

“…In addition, the intensity of a π–π stacking peak was significantly enhanced in the PT‐4F blend relative to the PT‐2F blend, which verifies well‐developed charge transport pathways through π‐orbital overlaps and correlates with the superior electrical performances of the PT‐4F‐based devices. [ 34 ] The increase of the (010) coherence length ( L c,(010) ) value from the PT‐2F blend (4.3 nm) to the PT‐4F blend (4.7 nm) supports the better molecular packing of the PT‐4F blend. [ 35 ] These beneficial crystalline characteristics of the PT‐4F blend originate from those of the pristine PT‐4F film, which showed a shorter d 010 of 3.64 Å and longer L c,(010) of 6.5 nm compared to those ( d 010 = 3.74 Å and L c,(010) = 5.9 nm) of the pristine PT‐2F film (Figure S14 and Table S14, Supporting Information).…”

Material Design and Device Fabrication Strategies for Stretchable Organic Solar Cells

“…The introduction of conjugation‐break spacers (CBSs) is another effective strategy to reduce the excessive backbone rigidity of polymers. [ 77,81,82,101d,105 ] The addition of a limited number of CBSs does not significantly impair the charge transport ability of polymers. This is because the effective conjugation length is generally shorter than the total length of the polymer chains due to torsional disorder and chemical defects.…”

“…[ 81,105c,l ] Compared to P3HTT‐ehDPP‐10%:PC 61 BM binary blend films that showed only 10% COS, the ternary blend films with 10−25% of CBS‐containing polymers showed dramatically enhanced COS values. [ 81 ] In addition, the PCEs of OSCs based on the ternary blends were comparable to or even higher than those of OSCs based on the binary blends while demonstrating high stretchability. For example, when 10% of P5 (40% T‐8‐T/40% dtdDPP) polymer was added to the binary blend, the PCE was increased from 4.35% to 4.82%, and the ternary blend showed a surprisingly high COS of 398%.…”

“…[ 115,116 ] However, the design of well‐functioning ternary blends for f‐SOSCs is still very challenging as both the stretchability and photovoltaic properties of the blend films should be optimized. [ 41,60,62,67,75,81,83,85,118 ]…”

“…[115,116] However, the design of well-functioning ternary blends for f-SOSCs is still very challenging as both the stretchability and photovoltaic properties of the blend films should be optimized. [41,60,62,67,75,81,83,85,118] Ade and O'Connor et al investigated a 2D/1A ternary system using IT-M as a sole acceptor, with which two P D s (i.e., FTAZ and PBDB-T) were blended in various ratios. [67] Compared to the reference FTAZ:IT-M (1:1) binary blend with a PCE of 11.8% and COS of 33%, the optimized ternary FTAZ:PBDB-T:IT-M (0.8:0.2:1) blend achieved an enhanced PCE of 13.2% and a comparable COS of 29%.…”