“…Up to date, various HTL materials have been used in this kind of solar cells, including organic (such as 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), Poly(3,4-ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS), poly[bis(4phenyl)(2,4,6-trimethylphenyl)amine (PTAA), Poly[bis(4-phenyl) (4-butylphenyl)amine] (PTPD), poly(3-hexylthiophene) (P3HT)), inorganic (such as CuX (X = I or S), CuXCN (X = S or Se), MxOy (M = Ni, Mo, V, Co, or Cu), and CuMO 2 (M = Ga, Cr, or Al)) HTL materials, and the organic:inorganic hybrid ones. [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] The organic HTLs have potential advantages in humidity-proof for stability and deep highest occupied molecular orbital (HOMO) to reach large V oc , [27] but the high-cost organic semiconductors themselves are not photothermally stable when exposed to the air infiltrated through mesoporous carbon. Besides, the charge mobility (10 −4 -10 −3 cm −2 V −1 S −1 ) is also relatively poor compared with the inorganic HTL materials.…”