A Quinoxaline‐Based D–A Copolymer Donor Achieving 17.62% Efficiency of Organic Solar Cells

Abstract

Side‐chain engineering has been an effective strategy in tuning electronic energy levels, intermolecular interaction, and aggregation morphology of organic photovoltaic materials, which is very important for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). In this work, two D–A copolymers, PBQ5 and PBQ6, are designed and synthesized based on bithienyl‐benzodithiophene (BDTT) as the donor (D) unit, difluoroquinoxaline (DFQ) with different side chains as the acceptor (A) unit, and thiophene as the π‐bridges. PBQ6 with two alkyl‐substituted fluorothiophene side chains on the DFQ units possesses redshifted absorption, stronger intermolecular interaction, and higher hole mobility than PBQ5 with two alkyl side chains on the DFQ units. The blend film of the PBQ6 donor with the Y6 acceptor shows higher and balanced hole/electron mobilities, less charge carrier recombination, and more favorable aggregation morphology. Therefore, the OSC based on PBQ6:Y6 achieves a PCE as high as 17.62% with a high fill factor of 77.91%, which is significantly higher than the PCE (15.55%) of the PBQ5:Y6‐based OSC. The PCE of 17.62% is by far one of the highest efficiencies for the binary OSCs with polymer donor and Y6 acceptor.

Stable perovskite solar cells with efficiency of 22.6% via quinoxaline-based polymeric hole transport material

“…The VBM energy levels (E VBM ) of PBQ5, PBQ6 and PBQ10 were determined by ultraviolet photoelectron spectroscopy (UPS), and the values of E VBM were measured to be −5.31, −5.43 and −5.25 eV, respectively (Figure S3). According to the previous report, the optical bandgaps of PBQ5, PBQ6 and PBQ10 were 1.88, 1.71 and 1.93 eV, respectively [61]. The conduction band minimum (CBM) energy level (E CBM ) could be calculated by E CBM = E VBM − E g .…”

“…Molecular structures of the polymer HTMs (PBQ5, PBQ6 and PBQ10) are shown in Figure 1a. The synthetic procedures of PBQ5, PBQ6 and PBQ10 are following the previously published literature [60,61]. All of the three D-A copolymer HTMs PBQ5, PBQ6 and PBQ10 are composed of the BDTT with bi-alkyl-fluorothienyl side chains as D unit, DFQ with different side chains as A-unit and thiophene as the π-bridge.…”

“…The results are included in Figures S5, S6 and Table S1 (Supporting Information online). The polymer HTMs PBQ5 and PBQ6 exhibit clear molecular crystalline order and preferential face-on molecular orientation with well-defined (010) π-π stacking diffraction peaks in the out-of-plane (OOP) direction, which is supposed to contribute to efficient charge transport in the vertical direction of the substrate [61]. The crystal coherence length (CCL) of PBQ5 and PBQ6 in the OOP direction are calculated to be 15.09 and 19.20 Å, respectively, indicating that PBQ6 exhibit the higher degree of molecular self-assembly and crystallinity, which is favorable to the charge transport and also consistent with the hole mobility results.…”

“…Therefore, Sun et al [60] further synthesized a new D-A copolymer PBQ10 with bi-alkyl-fluorothienyl-substituted BDTT as a D-unit and alkoxy-substituted DFQ as an A-unit, and PBQ10 as a donor demonstrated a high PCE of 16.34% in the corresponding organic solar cells. Recently, we synthesized two new PBQ-series D-A copolymers PBQ5 and PBQ6 with bi-alkyl and bi-alkyl-fluorothienyl side chains respectively on the DFQ A-unit [61], and we found that the electronic energy levels and hole mobilities of the polymers can be tuned effectively by the different side chains.…”

Binary and Ternary Polymer Solar Cells Based on a Wide Bandgap D‐A Copolymer Donor and Two Nonfullerene Acceptors with Complementary Absorption Spectral

“…In recent years, with the emergence of nonfullerene small molecule acceptors (NFSMA), [1][2][3][4][5][6][7] and non-fullerene polymers, [8,9] polymer solar cells (PSCs) based on bulk heterojunction (BHJ) have attained rapid development in power conversion efficiency (PCE) in the range of 17-18 % [10][11][12][13][14][15][16] for single junction based active layers. It is predicted that after the selection of appropriate polymer donor and NFSMAs, the PCE can be increased upto 20 % with high stability [17,18] and may be the potential candidate for future eco-friendly commercial application in indoor as well greenhouses.…”