Simple Nonfused Ring Electron Acceptors with 3D Network Packing Structure Boosting the Efficiency of Organic Solar Cells to 15.44%

Abstract

Zhan et al. reported a fused ring electron acceptor (FREA) ITIC with an acceptordonor-acceptor (A-D-A) type structure. [1] Subsequently, numerous FREAs are developed by researchers, which largely promoted the photovoltaic performance of OSCs. Recently, Zou et al. developed a series of A-DA′D-A type FREAs (Y6 series). Up to now, the highest power conversion efficiency (PCE) of OSCs based on FREAs has reached 18%, demonstrating the bright future for practical application. [2][3][4][5][6][7][8][9] Although FREAs can achieve high efficiency, they are expensive and their syntheses are complicated, which usually includes low-yield ring-closure reactions. For the commercialization of OSCs, it is highly desired to develop highperformance and low-cost nonfullerene acceptors. Therefore, we want to develop simple nonfused ring electron acceptors (NFREAs) to replace the high-cost FREAs. In 2017, we first postulated and proved that intramolecular noncovalent interactions could be used to partially replace chemical bonds to synthesize NFREAs. [10] Since then, small fused ring building blocks such as indacenodithiophene (IDT), [11][12][13][14] cyclopentadithiophene (CPDT), [15][16][17][18][19][20][21][22][23][24] etc., were often used for the construction of NFREAs. Later, researchers also developed fully nonfused ring electron acceptors. [25][26][27] However, the photovoltaic performance of the solar cells based on NFREAs is still far behind the FREAs.Typical FREAs consist of a fused ring core, side chains, and two electron-withdrawing terminal groups. [28][29][30][31] The planar fused ring core is beneficial for the electron delocalization. The side chain can increase the solubility and affect the molecular stacking of acceptors. The electron-withdrawing terminal group such as 3-(1,1-dicyanomethylene)-5,6-difluoro-1-indanone can induce a strong intramolecular charge transfer (ICT) effect in the acceptor molecule, which can remarkably broaden the absorption, lower the energy levels (especially the lowest unoccupied molecular orbital (LUMO)), and enhance the molecular stacking. [32][33][34] Besides these basic characteristics, recent reports begin to focus on molecular stacking model. There is growing evidence that high-performance FREAs possess a 3D network packing structure, being in favor of facilitating multiple charge transport, achieving small exciton binding energy, and reducing energy loss in OSCs. [5,[35][36][37][38][39] Unlike rigid FREAs, the molecular Three nonfused ring electron acceptors (NFREAs; 2Th-2F, BTh-Th-2F, and 2BTh-2F) with thieno[3,2-b]thiophene bearing two bis(4-butylphenyl)amino substituents as the core, 3-octylthiophene or 3-octylthieno[3,2-b]thiophene as the spacer, and 3-(1,1-dicyanomethylene)-5,6-difluoro-1-indanone as the terminal group are designed and synthesized. The molar extinction coefficient of acceptors and the electron mobility of blend films gradually increase with increasing π-conjugation length. Moreover, 2BTh-2F displays a planar molecular conformation assisted by S•••N and S•••O intr...

Recent progress in organic solar cells based on non-fullerene acceptors: materials to devices

“…Bo et al synthesized unfused SMAs 2BTh-2F, which shows a 3D network packing. 70 The devices of D18: 2BTh-2F gave a PCE of 15.44%, which was the highest value reported for solar cells based on unfused-ring small molecule acceptors. The chemical structures of unfused-ring SMAs are shown in Fig.…”

Unfused Acceptors Matching π‐Bridge Blocks with Proper Frameworks Enable Over 12% As‐Cast Organic Solar Cells

“…[19][20][21][22][23][24][25][26][27] Compared with rigid FREAs, UFAs adopt intramolecular noncovalent interactions) to ensure their coplanar backbones for high carrier mobility. [28][29][30][31][32][33][34][35] At present, the state-of-theart UFAs have pushed the maximum PCE to 15.44% after careful device optimization. [32] Currently, most high-efficiency OSCs depend on device optimization including additives usage, spin-coating with hot solutions or on hot plates, and thermal annealing.…”

“…[28][29][30][31][32][33][34][35] At present, the state-of-theart UFAs have pushed the maximum PCE to 15.44% after careful device optimization. [32] Currently, most high-efficiency OSCs depend on device optimization including additives usage, spin-coating with hot solutions or on hot plates, and thermal annealing. [20][21][22]32,36] However, some additives may cause environmental pollution, while thermal annealing and hot spin-coating may increase energy consumption and process complexity.…”

“…[32] Currently, most high-efficiency OSCs depend on device optimization including additives usage, spin-coating with hot solutions or on hot plates, and thermal annealing. [20][21][22]32,36] However, some additives may cause environmental pollution, while thermal annealing and hot spin-coating may increase energy consumption and process complexity. The exploring high-performance UFAs is highly demanding for as-cast OSCs, thus raising higher requirements for their structure design.For the development of UFAs, many up-and-coming building blocks have emerged.…”

Designing Efficient Tandem Organic Solar Cells with Machine Learning and Genetic Algorithms

“…This unit led to a slightly twisted backbone, adopting a 3D conformation that suppressed over-aggregation, allowing for an efficient charge transport network. Since this project has been completed, a new record-breaking unfused NFA has been published with unit 28 as its central backbone, giving a PCE of 15.44% with donor D18 62 . The other top unfused units (ESI Fig.…”