Sci Rep 2012, 2:1004.CrossRef Competing interests The authors declare that they have no competing interests. Authors’ contributions I-FC conceived and designed the experiments. R-JL and T-YC performed the DEP and Raman/SERS experiments, respectively. I-FC and H-WW wrote the paper and supervised this study. All authors read and approved the final manuscript.”
“Background The performance of organic solar cells find more significantly improved during the last few years. Both industrial and academic sectors have focused on the enhancement of their performance, developed new materials, and also improved the stability of the devices. Organic solar cells have

attracted a huge interest, given that they this website are easy to make on flexible substrates, using roll-to-roll technology [1–4], which significantly reduces the manufacturing costs [5, see more 6]. Although we have seen a significant improvement in the performance of organic solar cells, the efficiency of organic solar cells is still far behind their counterparts, inorganic solar cells. Organic solar cells are basically fabricated by sandwiching a photoactive layer between two electrodes. Normally, in the conventional device architecture, a poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) layer is employed

as an anode buffer layer [7–9]. However, one major drawback of using PEDOT:PSS is its poor stability. Therefore, another alternative to avoid the use of PEDOT:PSS is to make use of an inverted structure [10–22], where the anode and cathode positions

are reversed, and n-type metal-oxide-semiconductors, Celastrol namely, ZnO, TiO x , AZO, and NiO x , are used [2–5], instead of the PEDOT:PSS. Despite device architecture, there is another factor which one can consider in order to enhance the performance of optoelectronic devices, which is the energy barrier between layers. One may find that by decreasing this energy barrier, charge carrier injection at the interface can be significantly improved and therefore, device performance can be improved [23–26]. To date, various methods have been introduced to tune the work functions between semiconductors and metals such as plasma treatment, absorption of atoms, and also the introduction of additional thin-films [27–31]. Zinc oxide (ZnO) has attracted considerable interest for its optical, electrical, and mechanical properties. Experimental and theoretical studies on ZnO crystals have revealed the presence of a permanent dipole moment, which yields a significant piezoelectric effect for a variety of mircomechanical devices. ZnO has been shown to be a good electron selective and hole blocking contact in inverted solar cells. The conduction band (CB) and valence band (VB) of ZnO have been reported to be −4.4 and −7.8 eV, respectively [15]. This allows ZnO to function as a good interfacial layer between ITO and the bulk-heterojunction blend for inverted solar cell devices.