Interfacial Layer Materials with a Truxene Core for Dopant-Free NiO_x-Based Inverted Perovskite Solar Cells

Nickel oxide (NiOx) is commonly used as a holetransporting material (HTM) in p-i-n perovskite solar cells. However, the weak chemical interaction between the NiOx and CH3NH3PbI3 (MAPbI(3)) interface results in poor crystallinity, ineffective hole extraction, and enhanced carrier recombination, which are the leading causes for the limited stability and power conversion efficiency (PCE). Herein, two HTMs, TRUX-D1 (N-2,N-7,N-12-tris(9,9-dimethyl-9H-fluoren-2-yl)-5,5,10,10,15,15-hexaheptyl-N-2,N-7,N-12-tris(4-methoxyphenyl)-10,15-dihydro-5H-diindeno[1,2-a:1 ',2 '-c]fluorene-2,7,12-triamine) and TRUX-D2 (5,5,10,10,15,15-hexaheptyl-N-2,N-7,N-12-tris(4-methoxyphenyl)-N-2,N-7,N-12-tris(10-methyl-10H-phenothiazin-3-yl)-10,15-dihydro-5H-diindeno[1,2-a:1 ',2 '-c]fluorene-2,7,12-triamine), are designed with a rigid planar C-3 symmetry truxene core integrated with electron-donating amino groups at peripheral positions. The TRUX-D molecules are employed as effective interfacial layer (IFL) materials between the NiOx and MAPbI(3) interface. The incorporation of truxene-based IFLs improves the quality of perovskite crystallinity, minimizes nonradiative recombination, and accelerates charge extraction which has been confirmed by various characterization techniques. As a result, the TRUX-D1 exhibits a maximum PCE of up to 20.8% with an impressive long-term stability. The unencapsulated device retains 98% of their initial performance following 210 days of aging in a glove box and 75.5% for the device after 80 days under ambient air condition with humidity over 40% at 25 degrees C.