PTB7-Th-Based Organic Photovoltaic Cells with a High V_OC of over 1.0 V via Fluorination and Side Chain Engineering of Benzotriazole-Containing Nonfullerene Acceptors

Abstract

PTB7-Th is considered one of the most classic donor polymers for organic photovoltaic (OPV) cells. However, the power conversion efficiency (PCE) of PTB7-Th-based OPV is lagging behind that of other promising polymers mainly because of the relatively low open-circuit voltage (V OC). To increase the V OC and PCE of PTB7-Th-based OPV, the development of nonfullerene acceptors (NFAs) and studies of structure–property–performance relationship are vital. Here, three A2-A1-D-A1-A2-type acceptors, namely BTA45, F-BTA45, and F-BTA5, were developed by fluorination on the benzotriazole (BTA) unit and regulating alkoxy or alkyl phenyl side chains. Compared with BTA45, light absorption and π–π packing can be simultaneously improved for the two fluorinated BTA acceptors, resulting in an increased J SC and FF. Moreover, the F-BTA5-based blend film exhibits better phase separation morphology and electron transport than those of BTA45 and F-BTA45, which contribute to a device efficiency of 10.36% with a V OC of 1.03 V. In addition, the ΔE 2 values of the three blends are less than 0.15 eV, together with their moderate ΔE 3, efficiently decreasing their energy loss. These results highlight the importance of fluorination and side chain engineering for NFAs to boost the V OC and PCE for low-band gap photovoltaic polymers.

The Effect of Silicon Substitution in Indacenodithiophene‐Based A2‐A1‐D‐A1‐A2‐Type Nonfullerene Acceptors on the Performance of High‐Voltage Organic Solar Cells

“…Theoretically, the elevated LUMO energy level of the BTA502 could facilitate the achievement of higher V OC of the device without considering energy losses. In addition, the HOMO/LUMO values of the broadband gap donor J52‐F [ 31 ] and the narrow‐bandgap donor PTB7‐Th [ 32 ] are −5.29/−3.38 and −5.23/−3.52 eV, respectively. The energy‐level diagram of the corresponding material was shown in Figure 1d, and the bandgaps calculated by different methods were summarized in Table 1 .…”

“…1) The large-conjugated IDT or SiIDT frameworks containing linear alkyl side chains have a little steric hindrance, which is conducive to π-π stacking and further enhancing charge transport; 2) The fluorinated BTA-based π bridge units adjust the energy levels and strengthen the intermolecular interaction, which could improve molecular crystallinity; and 3) The benzyl end groups tune the method of molecular stacking, which is more beneficial to efficient charge transport and optimized phase separation morphology. [29,30] In addition, to comprehensively and reasonably explore the generalizability of the effect of heteroatom Si substitution on photovoltaic performance, a classic wide-bandgap donor J52-F [31] and a narrow-bandgap donor PTB7-Th [32] were selected for the preparation of high-voltage OSCs by coblending with the aforementioned two NFAs, respectively.…”

A review on organic photovoltaic cell

“…Donors are generally classified according to band gap and are known as wide band gap (> 1.8 eV), such as poly (3‐hexylthiophene) (P3HT) 29,59 mid‐band gap (1.6‐1.8 eV), such as poly [N‐9′‐heptadecanyl‐2,7‐carbazol‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazol)] (PCDTBT) 66,67 ; or narrow band gap (<1.6 eV), such as poly[[4,8‐bis [(2‐ethylhexyl) oxy] benzo [1,2‐b: 4,5‐b'] dithiophene‐2,6‐diyl] [3‐fluoro‐2‐[(2‐ethylhexyl) carbonyl] thieno [3,4‐b] thiophenediyl]] (PTB7) 68,69 . Other donor materials that are intensively studied include poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylene vinylene] (MEH‐PPV), 70 poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV) 64 …”

“…OPVs, which generate clean, renewable, and sustainable energy, 33,41,45,108,156‐160 have the potential to change the organic photovoltaics market, 33 as this emerging technology has numerous benefits over conventional inorganic semiconductor‐based systems 12,138 . OPVs have a short energy payback time, 33,162 they can absorb light across the solar spectrum, 64 their fabrication cost is low 35,46,92,114,136,158,16‐169 and simple, 28,92,11,73,138,160,165,170 due to the use of abundant materials, 22 can be manufactured using solution‐based processing, 62,63,72,156,165,171,17 do not require high manufacturing temperatures,…”

Carboxylate-Containing Wide-Bandgap Polymers for High-Voltage Non-Fullerene Organic Solar Cells

“…By integrating halogenation and carboxylation, the target polymers are expected to produce deep HOMO levels, strong crystallinity, and fast charge transport. We selected the wide-band gap BTA-based molecules BTA5 and F-BTA5 owing to high-lying lowest unoccupied molecular orbital (LUMO) levels. Thus, the four material combinations have the potential to obtain a high V OC of over 1.10 V due to the large energy offsets between the HOMO level of the donor and the LUMO level of the acceptor.…”