Efficient and ultraviolet durable inverted organic solar cells based on an aluminum-doped zinc oxide transparent cathode

High performance inverted bulk heterojunction organic solar cells (OSCs), based on the blend of poly[[4,8-bis[(2-ethylhexyl)oxy] benzo [1,2-b:4,5-b′] dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl]] (PTB7): 3′H-Cyclopropa[8,25] [5,6]fullerene-C70-D5h(6)-3′-butanoicacid, 3′-phenyl-, methyl ester (PC₇₀BM), were achieved using an aluminum-doped zinc oxide (AZO) front transparent cathode. A structurally identical PTB7:PC₇₀BM-based OSC having an indium tin oxide (ITO) front cathode was also made for comparison studies. The surface of AZO and ITO was modified with a 10 nm thick solution-processed ZnO interlayer to facilitate the efficient electron extraction. This work yielded AZO-based OSCs with a promising power conversion efficiency of 6.15%, slightly lower than 6.57% of a control ITO-based OSC, however, a significant enhancement in the stability of AZO-based OSCs was observed under an ultraviolet (UV)-assisted acceleration aging test. The distinctive enhancement in the lifetime of AZO-based OSCs arises from the tailored absorption of AZO electrode in wavelength <380 nm, serving as a UV filter to inhibit an inevitable degradation in ITO-based OSCs caused by the UV exposure.