Elucidating End-Group Modifications of Carbazole-Based Nonfullerene Acceptors in Indoor Applications for Achieving a PCE of over 20%

In this work, two DTSiC-based nonfullerene acceptors (NFAs), (2,2′-((2Z,2′Z)-((12-(heptadecan-9-yl)-4,4,7,7-tetraoctyl-7,12-dihydro-4H-thieno[2′,3′:4,5]silolo[3,2-b]thieno[2′,3′:4,5]silolo[2,3-h]carbazole-2,9-diyl)bis(methaneylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) (DTSiC-IC) and (2,2′-((5Z,5′Z)-((12-(heptadecan-9-yl)-4,4,7,7-tetraoctyl-7,12-dihydro-4H-thieno[2′,3′:4,5]silolo[3,2-b]thieno[2′,3′:4,5]silolo[2,3-h]carbazole-2,9-diyl)bis(methaneylylidene))bis(6-oxo-5,6-dihydro-4H-cyclopenta[c]thiophene-5,4-diylidene))dimalononitrile) (DTSiC-TC), are designed with various end groups (IC and TC). To explore the effect of end-group modifications, photovoltaic performance under AM 1.5G and indoor conditions are comprehensively studied. Compared with DTSiC-IC, DTSiC-TC manifests red-shifted and stronger absorption, downshifted lowest unoccupied molecular orbital (LUMO), and pronounced face-on packing characteristics. As we envisaged, the PM7:DTSiC-TC-based devices outperform the PM7:DTSiC-IC-based devices in both AM 1.5G and indoor (light-emitting diode (LED) 3000 K 1000 lux) conditions with overall higher JSC, FF, and power conversion efficiency (PCE). Furthermore, the PM7:DTSiC-TC-based devices achieve an outstanding PCE of 20.73% with a VOC of 0.87 V, a JSC of 0.095 mA/cm2, and an FF of 70.86%.