Morphology optimization of photoactive layers in organic solar cells

Organic solar cells(OSCs)have unique advantages of light weight,low-cost solution processing,and capability to be fabricated into flexible and semitransparent devices,which are widely recognized as a promising photovoltaic technology.Photoactive layers of the OSCs are composed of a blend of a p-type organic semiconductor as a donor(D)and an n-type organic semiconductor as acceptor(A).The morphology of the active layer with D/A nano-scaled aggregation and face-onπconjugated packing,and D/A interpenetrating network is crucial for achieving high photovoltaic performance of the OSCs.Therefore,great efforts have been devoted to control and optimize morphology of the active layers.This perspective focuses on the morphological control by solvent/solid processing additives and the morphology optimization by postdeposition treatment with thermal annealing and/or solvent vapor annealing,which have been extensively adopted and exhibit promising positive effect in optimizing the morphology.Representative examples are given and discussed to understand the foundation of the postdeposition treatments on tuning the morphology.Insights into the role of the postdeposition treatments and additive treatments on the morphology optimization will be beneficial to further improvement in morphology optimization for practical organic photovoltaic application.

Enhancement of photovoltaic performance by two-step dissolution processed photoactive blend in polymer solar cells

We reported enhanced performance of polymer solar cells, based on poly(3-hexylthiophene):[6,6]-phenylC_(61)-butyric acid methyl ester(P3HT:PC_(61)BM) and polythieno[3,4-b]-thiophene-co-benzodithiophene:[6,6]-phenylC_(71)-butyric acid methyl ester(PTB7:PC_(71)BM) photovoltaic systems, by a two-step dissolution treatment of photoactive blends. Optical and morphological characterization revealed that the composition of the ordered polymer and donor/acceptor phase structure in the photoactive layer can be optimized using a two-step dissolution treatment. In addition, time-resolved photoluminescence indicated that exciton dissociation efficiency could be increased using this method. Current density-voltage(J-V) measurements showed that power conversion efficiencies(PCE) of the two-step dissolution treated devices were higher than those of one-step treated devices by 24% and 8% for P3HT:PC61BM and PTB7:PC_(71)BM systems, respectively. Therefore, this two-step dissolution treatment further optimizes the performance of polymer solar cells.

Fabrication of Zn-Ti layered double hydroxide by varying cationic ratio of Ti^(4+) and its application as UV absorbent

ZnTi-layered double hydroxides（LDHs） with varying Zn/Ti ratio have been synthesized by coprecipitation of zinc and titanium salts from homogeneous solution.The obtained ZnTi-LDHs possess high crystallinity and hierarchical structure with improved UV-absorbance property.The UV-vis spectra show that the UV absorbing properties of ZnTi-LDHs is stronger and broader than both MgAl-LDH and ZnAl-LDH due to the existence of Ti.Moreover,the UV absorption property increased with the content of Ti,which can be ascribed to the decrease in the band gap energy,as clearly confirmed by density functional theory calculations.When irradiated by UV rays,the property of the samples with generated free radicals（OH^·and O2^·） was evaluated by means of electron spin resonance（EPR）.ZnTi-LDHs generated a relatively lower active radicals in contrast with TiO2 and ZnO,which implied an increased safety used as sunscreens.Therefore,this work provides a detailed understanding of UV shielding properties of ZnTiLDHs which was unrevealed previously,and demonstrates the expansive application prospects of ZnTiLDHs in the field of sunscreens.