Ternary Nonfullerene Polymer Solar Cells with 12.16% Efficiency by Introducing One Acceptor with Cascading Energy Level and Complementary Absorption

Abstract

A novel small-molecule acceptor, (2,2'-((5E,5'E)-5,5'-((5,5'-(4,4,9,9-tetrakis(5-hexylthiophen-2-yl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(4-(2-ethylhexyl)thiophene-5,2-diyl))bis(methanylylidene)) bis(3-hexyl-4-oxothiazolidine-5,2-diylidene))dimalononitrile (ITCN), end-capped with electron-deficient 2-(3-hexyl-4-oxothiazolidin-2-ylidene)malononitrile groups, is designed, synthesized, and used as the third component in fullerene-free ternary polymer solar cells (PSCs). The cascaded energy-level structure enabled by the newly designed acceptor is beneficial to the carrier transport and separation. Meanwhile, the three materials show a complementary absorption in the visible region, resulting in efficient light harvesting. Hence, the PBDB-T:ITCN:IT-M ternary PSCs possess a high short-circuit current density (J ) under an optimal weight ratio of donors and acceptors. Moreover, the open-circuit voltage (V ) of the ternary PSCs is enhanced with an increase of the third acceptor ITCN content, which is attributed to the higher lowest unoccupied molecular orbital energy level of ITCN than that of IT-M, thus exhibits a higher V in PBDB-T:ITCN binary system. Ultimately, the ternary PSCs achieve a power conversion efficiency of 12.16%, which is higher than the PBDB-T:ITM-based PSCs (10.89%) and PBDB-T:ITCN-based ones (2.21%). This work provides an effective strategy to improve the photovoltaic performance of PSCs.

Morphology Control Enables Efficient Ternary Organic Solar Cells

“…[6][7][8] For instance, devices based on a number of novel nonfullerene acceptor (NFA) materials have been recently reported with PCEs exceeding 12%, [9][10][11][12][13][14][15][16][17] which outperformed the photovoltaic performance of fullerene-based OSCs. [54] These results highlight bright future for NFAs' application in ternary solar cells. [53] These two NFAs are miscible and formed a homogeneous mixed phase, resulting in superior device performance, which offers a new direction in device optimization.…”

Two Well‐Compatible Acceptors with Efficient Energy Transfer Enable Ternary Organic Photovoltaics Exhibiting a 13.36% Efficiency

“…According to the role of the third component in performance improvement, it can be divided into two categories: (i) as morphology regulator to optimize phase separation degree for achieving apparent fill factor (FF) improvement and relatively weak short‐circuit current density ( J SC ) improvement; (ii) as photon harvesting enhancer to mainly achieve J SC improvement based on the complementary absorption spectra of used materials. The highest occupied molecular orbital levels of two donors or the lowest unoccupied molecular orbital levels of two acceptors should be very similar for efficient intermolecular charge transfer or transport in ternary active layers . According to the previous reports, the good compatibility, complementary photon harvesting range and well‐matched energy levels of used materials should be comprehensively considered for achieving efficient ternary OPVs.…”

“…The dynamic processes of intermolecular energy transfer, charge transfer, and alloyed model are considered as the main aspect in efficient ternary OPVs, which strongly depends on intermolecular miscibility in ternary active layers . The compatibility of used materials will directly influence the intermolecular miscibility and phase separation degree in ternary active layers, which strongly determine the performance of ternary OPVs . To give more deep insight on the third component role in determining the performance of ternary OPVs, the development of ternary OPVs is summarized in Table 1 .…”

High‐Performance Green Solvent Processed Ternary Blended All‐Polymer Solar Cells Enabled by Complementary Absorption and Improved Morphology

“…However, the incorporation of a copolymer with a relatively narrow bandgap will lead to a low open‐circuit voltage ( V OC ) due to the increased highest occupied molecular orbital (HOMO) energy level. In this respect, the overall efficiency of ternary blended all‐PSCs typically lower than those of their state‐of‐the‐art binary counterparts . Another critical issue responsible for the moderate efficiency of ternary blended all‐PSCs is the suboptimal morphology of the multi‐polymer blend films, which may lead to decreased fill factor of the resulting devices.…”