Benzodithiophene‐Based Polymers Containing Alkylthiophenyl Side Chains with Lowered HOMO Energy Levels for Organic Solar Cells

Abstract

In this paper,anovel donor based on alkylthiophenyl side-chainedb enzodithiophene (BDT) (M1) was first designed and synthesized to construct as eries of conjugated polymers (P1, P2, P3) used in polymer solar cells (PSCs). P1, P2, and P3 werep repared by copolymerizing M1 with 4,7-di(4-(2-ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole (DTBT), quinoxaline, and diketopyrrolopyrrole (DPP), respectively.T he optical electrochemical and photovoltaic properties of these polymers were investigated.A lkylthiophenyl substitution on the BDT building block is favorable for the low-lying highest occupied orbital (HOMO) level of polymers. The HOMO of these copolymers is clearly lowered to À5.49 eV, À5.34 eV,a nd À5.50 eV,r espectively.C ompared with reference polymers, our polymerss how loweredH OMO energy levels (by 0.14 eV at least). This is very helpful to enhance the open-circuit voltage (V oc )o ft he devices. Further, P2:PC 61 BM exhibited an optimized power conversion efficiency( PCE) of 4.28 %, which is clearly higher than that of P1 (1.48 %) and P3 (1.9 %).

Research progress and application of high efficiency organic solar cells based on benzodithiophene donor materials

“…Subsequently, based on the alkyl chain substituted PPD unit, PQ3 (2015) was reported by Liu et al [136] ; PBDTBA(H)-DPP (2015) andPBDTBPA(F)-DPP (2015) were prepared by Chakravarthi et al [147] ; PBDTS-DPP (2016) ,PBDTOT-DPP (2016) and P2 (2016) were synthesized by Zhang et al [73] , Wang et al [148] and Kranthiraja et al [139] , respectively. Similarly,PBDTT-S-DPP (2016) , [149] PBDTT-Se-DPP (2016) , [149] P3 (2016) , [150] P7(0.0: 1.0) (2016) , [151] PDPP-BDT (2021) [152] and PDPP-BDT-Cl (2021) [152] were also prepared in subsequence. Notably, although the alkyl-based, selenophene-based, or benzene-based side chains with a wide conjugated plane endow such polymer donors: PCBM based OSCs with a moderate V oc (˜0.80 V), while the dispersed electron density reduces the J sc and FF .…”

“…In addition, Fan et al prepared P2 (2016) by introducing the side chain (2-hexyldecyl) (p -tolyl) sulfane into the BDT unit as well as 1-methyl-3-(octyloxy)benzene into the Qx unit, respectively. [150] Similarly, Aslan et al synthesized P1 (2022) by introducing selenophene-based and benzene-based side chains into the BDT and Qx unit in turn, [201] designing based on the theory that "Se"-based materials with strong interaction between "Se" and "Se" molecules not only extends the π-orbitals but also promotes hole/electron mobility. [84] After blending with acceptors, P2 (2016): PC 61 BM based and P1 (2022): PC 71 BM based OSCs obtained theV oc of 0.81 and 0.80 V,J sc of 7.72 and 8.39 mA/cm 2 ,FF of 68.79 and 60.8% and PCE of 4.28 and 4.10%, respectively.…”

“…In addition, based on the famous BTDz acceptor unit and its derivatives, Qu et al constructed the main chain BDT-TR-BTDz-TR, synthesizing two novel polymer donors PBDTC6DBT (2012) and PBDTC10DBT (2012) by introducing side chains 3-(methoxymethyl)heptane and hexyl into the BDT and π-bridge units in turn. [265] Subsequently, based on the reported results of PBDTC6DBT and PBDTC10DBT, a series of polymer donors PBDTT-BT (2013) , [266] PBDTF-BT (2013) , [266] P1 (2016) , [150] PBDT-DTBT (2017) , [267] PA (2017) , [80] PB (2017) , [80] PB3 (2017) , [137] PB3-S (2017) [137] and P1 (2017) [268] were also prepared by introducing thiophene-based, furan-based and benzene-based side chains into the BDT as well as solubilized alkyl chain into the π-bridge units, respectively. Moreover, Feng and coworkers innovatively designedPBDTEDOT-BT (2018) by introducing the 2,3-dihydrothieno [3, 4-b ] [1,4] dioxine based side chain into the BDT unit.…”

“…Furthermore, based on the most widely applied D-π-A-π type mian-chian engineering, PBDTPhBT1 (2010) , [277] PBDTPhBT2 (2010) , [277] PBDTTPT1 (2011) , [278] PBDTTPD2 (2011) , [278] PBDT-TBT-C6 (2011) , [153] PBDT-TBT-C8 (2011) , [153] PBDT-TBT-C10 (2011) , [153] PBDT-TBT-C12 (2011) , [153] O-HD (2011) , [144] BO-BO (2011) , [144] PU-O (2011) , [144] PBDT-TTBTT (2013) , [50] PBDT-tt-BT (2013) , [299] PDPPBDT (2014) , [146] P2(2014) , [162] POT-DH (2014) , [135] PBDT-TPD (2014) , [138] PBDT-ttTPD (2014) , [138] P1 (2015) , [157] P2 (2015) , [157] PV-BDTCl (2016) , [250] PBDTPH-DTQx (2016) , [221] PBDTPHO-DTQx (2016) , [221] P2 (2016) , [150] P11 (2019) [118] and BDT-T-Qx-T(P3) (2022) [201] were subsequently prepared to further exploring the potential effect by introducing side chains alkyl, alkyloxy and alkylthio. Notably, due to the substitution of alkyloxy group further improves the electron-donating of BDT unit, thus effectively optimizes the dissociation of exciton as well as hole/electron mobility, which endows PDPPBDT: PC 71 BM based and P11: PC 71 BM based OSCs with higherJ sc and FF than O-HD: PC 71 BM based, BO-BO: PC 71 BM based and PU-O: PC 71 BM based OSCs.…”

Challenging PM6-like donor polymers for pairing with a Y-type state-of-the-art acceptor in binary blends for bulk heterojunction solar cells

“…29,32 Thereafter, copolymer materials containing BDT units with phenyl flanking groups were demonstrated to have deeper HOMO levels and a higher V OC in the corresponding photovoltaic devices than those with thiophene substitutes, because of the weaker electron donor ability and the higher ionization potential of the phenyl-flanked BDT moiety. [33][34][35][36] However, until now there have been few papers discussing the effect of alkyl side chain modification in phenyl-flanked BDT units on the photovoltaic performance of NFA OSCs.…”