Fine-Tuning Semiconducting Polymer Self-Aggregation and Crystallinity Enables Optimal Morphology and High-Performance Printed All-Polymer Solar Cells

Abstract

Polymer aggregation and crystallization behavior play a crucial role in the performance of all-polymer solar cells (all-PSCs). Gaining control over polymer self-assembly via molecular design to influence bulk-heterojunction activelayer morphology, however, remains challenging. Herein, we show a simple yet effective way to modulate the selfaggregation of the commonly used naphthalene diimide (NDI)-based acceptor polymer (N2200), by systematically replacing a certain amount of alkyl side-chains with compact bulky side-chains (CBS). Specifically, we have synthesized a series of random copolymer (PNDI-CBS x ) with different molar fractions (x = 0−1) of the CBS units and have found that both solution-phase aggregation and solid-state crystallinity of these acceptor polymers are progressively suppressed with increasing x as evidenced by UV−vis absorption, photoluminescence (PL) spectroscopies, thermal analysis, and grazing incidence X-ray scattering (GIWAXS) techniques. Importantly, as compared to the highly self-aggregating N2200, photovoltaic results show that blending of more amorphous acceptor polymers with donor polymer (PBDB-T) can enable all-PSCs with significantly increased PCE (up to 8.5%). The higher short-circuit current density (J sc ) results from the smaller polymer phase-separation domain sizes as evidenced by PL quenching and resonant soft X-ray scattering (R-SoXS) analyses. Additionally, we show that the lower crystallinity of the active layer is less sensitive to the film deposition methods. Thus, the transition from spin-coating to solution coating can be easily achieved with no performance losses. On the other hand, decreasing aggregation and crystallinity of the acceptor polymer too much reduces the photovoltaic performance as the donor phase-separation domain sizes increases. The highly amorphous acceptor polymers appear to induce formation of larger donor polymer crystallites. These results highlight the importance of a balanced aggregation strength between the donor and acceptor polymers to achieve high-performance all-PSCs with optimal active layer film morphology.

10.13% Efficiency All‐Polymer Solar Cells Enabled by Improving the Optical Absorption of Polymer Acceptors

“…Regarding such SM acceptor‐based PSCs, the all‐polymer solar cells (all‐PSCs) consisting of a polymer donor and a polymer acceptor show unique advantages in the flexible large‐scale and wearable energy generators due to their excellent morphology stability and mechanical robustness . However, most of the efficient all‐PSCs have PCEs ranging in 8–10%, although a few of them achieved PCEs over 11%, which is still far behind that of the efficient PSCs based on SM acceptors due to the lack of high‐performance polymer acceptors. To date, polymer acceptors have been mainly confined into a small number of structural building blocks, and the most widely studied one is the polymer N2200 with a donor–acceptor (D–A) backbone of naphthalene diimide (NDI)‐ alt ‐bithiophene due to its NBG and suitable molecular energy levels .…”

Synergistically Improved Molecular Doping and Carrier Mobility by Copolymerization of Donor–Acceptor and Donor–Donor Building Blocks for Thermoelectric Application

“…Random copolymers are conventionally treated as irregular polymers with structural disorder along the backbone. Nevertheless, the large space for the adjustment of energy levels [29,30] and electrical properties [31][32][33] endows them with potentially enhanced TE behaviors. Herein, we introduce planar diketopyrrolopyrrole (DPP) as acceptor unit, thienothiophene and oligo ethylene glycol functionalized bithiophene as donor units, to synthesize a series of new random copolymers (Figure 1, bottom layer) consisting of DPP-TT (green shadow, abbreviated to DPP-TT in following text) and g 3 2T-TT building blocks (red shadow, abbreviated to g 3 2T-TT).…”

An Effective Method for Recovering Nonradiative Recombination Loss in Scalable Organic Solar Cells

“…[ 20 ] Unlike the strong crystallinity of IT‐4F, the lower crystallinity of the active layer is less sensitive to the printing approach. [ 21 ] Thus, ICBA is introduced to induce a desired morphology of active layer and reduce the voltage loss in blade‐coating devices. First, different proportions of ICBA are employed to blade coating, and the current density–voltage ( J – V ) curves are illustrated in Figure S2 in the Supporting Information.…”