Readily Accessible Benzo[d]thiazole Polymers for Nonfullerene Solar Cells with >16% Efficiency and Potential Pitfalls

Abstract

Here we report facile, high-yield synthetic access to the difluoro BTA building block, 4,7-bis­(5-bromo-4-(2-hexyl-decyl)-thiophen-2-yl)-5,6-difluoro-2-(pentadecan-7-yl)-benzo­[d]­thiazole (BTAT-2f), for use in donor (D)–acceptor 1 (A1)–D–acceptor 2 (A2) polymers [D = bithiophene; A1 = BTA-2f; A2 = benzothiadiazole (BT) derivative] for organic solar cells (OSCs). Fine tuning of polymer optical and electronic properties is achieved by incrementally varying the A2 fluorination level. Bulk-heterojunction (BHJ) PBTATBT-4f:Y6 solar cells deliver a noteworthy power conversion (PCE) efficiency of 16.08% (V oc = 0.81 V; J sc = 27.25 mAcm–2; FF = 72.70%) without processing additives. In contrast, PBTATBT-2f:Y6 exhibits an irregular morphology and low PCE, ascribable to cocrystal formation-induced recombination, which is unprecedented for nonfullerene (NFA) OSCs. This result should be of guiding significance for future NFA design.

On Charge Carrier Density in Organic Solar Cells Obtained via Capacitance Spectroscopy

“…In total, these six relevant methods to obtain the charge carrier density n are listed in Figure 4, where the first three (I-III) have already been used several times in past stu dies. [14,[17][18][19][20]27,31,32] The other three methods (IV-VI) are introduced to address the shortcomings mentioned earlier. The different total charge carrier densities n resulting from these methods for the investigated PTB7-Th:ITIC-2F and the PM6:Y6 solar cells are compared in Figure 5.…”

Optimized Active Layer Morphologies via Ternary Copolymerization of Polymer Donors for 17.6 % Efficiency Organic Solar Cells with Enhanced Fill Factor

“…Thus, to fully explore the photovoltaic potential of PM6 in OSCs, finely regulating the molecular structure to further optimize the corresponding active layer morphologies is of considerable significance. Although some molecular design strategies of polymer donors have been successfully implemented to achieve better the trade‐off among the V oc , J sc , and FF, such as heteroatom substitutions, [22a, 32, 45–47] side‐chain engineering, [41b, 48] and terpolymerization, [44, 49–51] further extensive studies are still necessary to in‐depth understand the reasons behind them.…”

Effect of main and side chain chlorination on the photovoltaic properties of benzodithiophene-alt-benzotriazole polymers

“…12 To enable practical applications, researchers have developed efficient, lower cost donor materials, such as the polymers PM6 and PTQ10. 6,[13][14][15][16][17] Preferably, electron donor and acceptor materials possess complementary optical absorption spectra to capture photons over a large part of the solar spectrum and have appropriate energy levels to promote exciton dissociation and charge separation. Furthermore molecular orientation, 18 molecular packing, and domain purity that are closely related to nanoscale morphology and charge carrier mobility, [19][20][21][22] strongly affect the photovoltaic performance.…”