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Electron-transporting small molecule bathophenanthroline (Bphen) together with o-xylene has been used as hybrid additives to improve the performance of simplified inverted polymer solar cells employing ITO alone as cathode and photoactive layer based on polymer [[2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b] dithiophene] [3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-Th) and (He et al., Nat. Photon. 9:174, 2015)-phenyl C-butyric acid methyl ester (PCBM). Because the Bphen additive could spontaneously aggregate onto the indium tin oxide (ITO) cathode during spin coating, the mixed solution containing PTB7-Th, PCBM, and Bphen, thereby forming a thin cathode-modifying layer, the ternary blend PTB7-Th:PCBM:Bphen functioned similar to a layered polyethylenimine ethoxylated (PEIE, a conventional cathode-modifying material)/binary blend PTB7-Th:PCBM combination. The o-xylene additive was confirmed to enrich the distribution of PTB7-Th donor towards the bottom area of photoactive layer, thereby benefiting the charge collection in inverted structure. With the o-xylene optimization, the PTB7-Th:PCBM:Bphen blend thin film showed a power conversion efficiency (PCE) of 5.87% in simplified inverted structure of ITO/photoactive layer/MoO/Ag, much higher than that (4.21%) of the PTB7-Th:PCBM blend thin film. The current research can be considered as a useful attempt towards fabricating low-cost photovoltaic devices without marked loss in PCE. [ABSTRACT FROM AUTHOR]

Inverted organic solar cells (OSCs) have been fabricated using the photoactive blend thin films based on regioregular poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and leuco-crystal violet (LCV). It was found that the LCV as an efficient n-dopant could significantly increase intrinsic electron concentration of PCBM zone. The electron mobility of P3HT:PCBM:LCV blend thin film was measured 1.75 times as high as that of P3HT:PCBM blend thin film, as a result of LCV-induced trap filling in the bandgap of PCBM. The power conversion efficiency for the inverted device using the photoactive layer of P3HT:PCBM:LCV could be 1.22 times as high as that for the inverted device using the conventional photoactive layer of P3HT:PCBM, mostly because (1) the higher electron mobility could enhance the exciton dissociation and thereby short-circuit current density in the former relative to the latter; (2) the increase in the electron concentration of PCBM zone in P3HT:PCBM:LCV blend thin film may help blocking holes diffusion towards cathode, improving the hole collection efficiency and thereby fill factor of device. We provide a new insight on optimizing the electron-conducting property of bulk-heterojunction photoactive thin film, useful for pushing forward inverted OSCs towards the cost-effective commercialization. [ABSTRACT FROM AUTHOR]