factor of 7. This shows that solution-based silicon is a highly promising candidate for industrial-grade applications of solutionbased semiconductors.
Evaluation of Precursors NPS and CPSIn literature, most groups reporting silicon fi lms fabricated from a liquid precursor use a cyclic hydridosilane, namely cyclopentasilane (CPS). We decided to use a branched molecule instead, namely neopentasilane (NPS). The molecular structures of CPS and NPS, as well as the process charts for obtaining solid amorphous silicon (a-Si) layers, are shown in Figure 1 . We characterized the NPS used in our process chain by NMR and by mass spectroscopy, showing the expected fi ngerprints mentioned in literature. [ 4 ] Employing NPS over CPS yields major advantages in processing effi ciency as well as in material quality. In general, branched molecules have a considerably better solubility in organic solvents, because the branches act as spacers, preventing strong interactions between the molecules and enabling better intercalation of solvent molecules. [ 5 ] The NPS material is therefore better soluble than CPS, which leads to improved fi lm homogeneity and uniformity. Moreover, in NMR measurements, we found that the NPS-oligomer bears 70% SiH 3 end groups, in contrast to 1.0% for the CPS-oligomer. Such end groups facilitate the cross-linking of the material to a solid network. Since this process is responsible for the formation of silicon-silicon bonds, we expect a positive effect on the coordination of silicon atoms, resulting in less dangling bonds and improved electronic properties. Until now, we have however not been able to demonstrate differences in nanoscopic amorphous silicon structure between CPS and NPS.Another major advantage of employing NPS instead of CPS lies in the differences in material synthesis. The synthesis of the CPS monomer involves a coupling reaction and subsequent chlorination of diphenyldichlorosilane to obtain decachlorocyclopentasilane. This process produces a large amount of various by-products, which are diffi cult to separate and recycle. However, in the synthesis of NPS, we use catalytic rearrangement of octachlorotrisilane to obtain dodecachloroneopentasilane,
We present a study on the performance and analysis of hybrid solar cells comprising a planar heterojunction between between a conjugated donor polymer, P3HT or PCPDTBT, and hydrogenated amorphous silicon (a-Si:H). A comparison of the modeled absorption spectra of the layer stack with the measured external quantum efficiency is used to investigate the contribution of the inorganic and organic material to the photocurrent generation in the device. Although both materials contribute to the photocurrent, the devices exhibit poor quantum efficiencies and low short circuit currents. Bandstructure simulations of the hybrid layer structure reveal that an unfavorable electric field distribution within the planar multilayer structure limits the performance. Using electroabsorption measurements we can show that the electric field is extremelyweak in the amorphous silicon but strong in the organic material. The situation changes drasticallywhen the conjugated polymer is p-doped. Doping not only increases the conductivity of the organic material, but also restores the electric field in the amorphous silicon layer. Optimized hybrid solar cells comprising thin doped P3HT layers exhibit energy conversion efficiencies (ECE) up to 2.8 %.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.