Determining Optimal Crystallinity of Diketopyrrolopyrrole-Based Terpolymers for Highly Efficient Polymer Solar Cells and Transistors

Abstract

A new series of conjugated random terpolymers (PDPP2T-Se-Th) was synthesized from electron-deficient diketopyrrolopyrrole (DPP) based unit in conjugation with two electronrich selenophene (Se) and thiophene (Th) species, with a view to inducing different crystalline behaviors of the polymers. The crystallinity of the polymers can be systematically controlled by tuning the ratio between Se and Th; an increase in Se content induced a remarkable increase in the melting and crystallization temperatures as well as the crystallinity of the PDPP2T-Se-Th terpolymers. These changes in the crystalline properties of polymers had a dramatic effect on the performances of organic field-effect transistors (OFETs) and polymer solar cells (PSCs). However, their effect on each type of devices was very different.The charge carrier mobilities of the PDPP2T-Se-Th terpolymers in OFET devices increased remarkably as the Se content increased in the polymers, showing that PDPP2T-Se100 with Se/Th ratio= 100/0 had very high hole and electron mobilities (4.72 and 5.54 cm 2 V -1 s -1 , respectively) with well-balanced ambipolar property. In contrast, the best power conversion efficiency (PCE) of 7.2% was observed for the PDPP2T-Se10-Th90 polymers that had Se/Th ratio of 10/90 due to the synergistic contributions from high charge mobility and optimized bulk-heterojunction (BHJ) morphology with fullerene acceptors. Therefore, the Se units in the polymer backbone could serve to (1) enhance charge carrier mobility and (2) optimize BHJ morphology, both of which affect the performance of the PSCs. To understand the effects of the crystallinity of random terpolymers on their performances in OTFTs and PSCs, we systematically investigated the effects of the Se/Th compositions on their optical, electrical, and structural properties.

Benzocyclobutene-fullerene bisadducts as novel electron acceptors for enhancing open-circuit voltage in polymer solar cells

“…The π-π stacking distance (010) of P3HT in both BCBCBA and bis-PCBM mixed film was calculated to be 0.38 nm (q z ¼1.65 Å À 1 ) from the out-of-plane plot, consistent with the literature values for well-ordered P3HT crystals [47][48][49]. For quantitative analysis of the crystalline order of P3HT, the crystal size of P3HT in each active layer was calculated using Scherrer equation [48,[50][51][52][53]. The detailed calculations are described in Supplementary materials.…”

Conjugated D–A terpolymers for organic field-effect transistors and solar cells

“…51 On the basis of transfer curves of the respective FETs, the charge carrier mobilities of thin films of P22a-P22c are higher than that of thin film of P22d, which is composed of alternating DPP and thiophene moieties, but terpolymers P22a-P22c exhibit lower charge mobilities than P22e and contain only selenophene as the electron donors. Such charge mobility enhancement is attributed to the improvement of interchain packing order degree for terpolymers containing different amounts of selenophene moieties in their backbones.…”

“…Among P22a-P22c, P22a displays relatively high photovoltaic performance, with a PCE of 7.2% after blending with PC 71 BM. 51 Some researchers have reported DPP-based terpolymers P23a-P23c with thiophene and anthracene units as co-electron donors. 52 The incorporation of anthracene units in the backbones of terpolymers will alter the interchain interactions and arrangements.…”

The Impact of Carrier Delocalization and Interfacial Electric Field Fluctuations on Organic Photovoltaics

“…45 There is some controversy in the literature regarding how crystallinity impacts BHJ efficiency, as there seems to be a tradeoff where increased crystallinity improves charge mobilities but decreases interfacial charge separation. [46][47][48][49][50][51] We wish to address some of the ways that increased crystallinity may affect charge separation here.…”