Understanding InP Nanowire Array Solar Cell Performance by Nanoprobe-Enabled Single Nanowire Measurements

III-V solar cells in the nanowire geometry might hold significant synthesis-cost and device-design advantages as compared to thin films and have shown impressive performance improvements in recent years. To continue this development there is a need for characterization techniques giving quick and reliable feedback for growth development. Further, characterization techniques which can improve understanding of the link between nanowire growth conditions, subsequent processing, and solar cell performance are desired. Here, we present the use of a nanoprobe system inside a scanning electron microscope to efficiently contact single nanowires and characterize them in terms of key parameters for solar cell performance. Specifically, we study single as-grown InP nanowires and use electron beam induced current characterization to understand the charge carrier collection properties, and dark current-voltage characteristics to understand the diode recombination characteristics. By correlating the single nanowire measurements to performance of fully processed nanowire array solar cells, we identify how the performance limiting parameters are related to growth and/or processing conditions. We use this understanding to achieve a more than 7-fold improvement in efficiency of our InP nanowire solar cells, grown from a different seed particle pattern than previously reported from our group. The best cell shows a certified efficiency of 15.0%; the highest reported value for a bottom-up synthesized InP nanowire solar cell. We believe the presented approach have significant potential to speed-up the development of nanowire solar cells, as well as other nanowire-based electronic/optoelectronic devices.

Distinctive expression of neoantigenic C3(D) epitopes on bound C3 following activation and binding to different target surfaces in normal and pathological human sera

Binding of C3 to sheep erythrocytes in a serum-free milieu (EAC14oxy2, EAC142) has previously been shown to mimic the antigenic change that occurs upon denaturation of C3 in sodium dodecyl sulphate (SDS), whereby neoantigenic C3(D) epitopes are exposed. The present paper deals with C3 bound to various target surfaces which are known to modulate the functional properties of C3 in different ways. Bound C3 fragments on serum-treated human aggregated gammaglobulin, zymosan, rabbit and sheep erythrocytes, and on circulating immune complexes isolated from sera of patients with rheumatoid arthritis and systemic lupus erythematosus, were shown to be mainly in the iC3b form. By RIAs, employing polyclonal antibodies, the range of C3(D) antigenic epitopes of 125I-labelled SDS denatured C3 expressed by the particle-bound iC3b was monitored. The physiologically bound iC3b on all tested particles expressed wide range of C3(D) epitopes and each type of particle-bound C3 exposed its individual range. By competition ELISA specific C3(D) alpha epitopes were monitored, employing monoclonal antibodies. A distinct difference in the expression of these epitopes was observed in iC3b bound to various test particles in the presence of normal serum and in iC3b present on circulating immune complexes from pathological sera. Considering that the neoantigenic C3(D) epitopes have been shown to be associated with different functions of C3, the distinctive antigenic expression of each type of serum-treated particle might reflect different functional forms of the protein.

A simplified assay for the detection of C3a in human plasma employing a monoclonal antibody raised against denatured C3

A monoclonal antibody raised against SDS-denatured C3 was shown to react with both solid-phase C3a and unfragmented C3. However, in the fluid phase the antibody was found to bind only to C3a and not to native C3. These findings indicated that the antibody could be used in an assay to detect C3a in human EDTA-plasma without prior separation of C3a from native C3. A simple and rapid competition ELISA was developed which monitored soluble C3a. 200 microliter of C3a (8 ng) was absorbed to plastic wells over night at 4 degrees C. Thereafter, 50 microliter of sample and 50 microliter of constant amounts of monoclonal antibody conjugated with beta-galactosidase, were incubated for 60 min at 37 degrees C. After washing, the colour reaction was started by adding nitrophenyl-galactopyridine to the wells. The microtitre plate was incubated at 37 degrees C for 30 min and the staining intensity was quantified at 405 nm. The assay detected both C3a and C3ades arg. A strong correlation was obtained between the new technique and an RIA which used an acid precipitation step for the separation of C3a prior to the determination of C3a (r = 0.9). Significantly higher levels of C3a were detected both in plasma from patients with immune complexes (93 +/- 9 ng/ml; P less than 0.1) and in plasma from patients treated in blood oxygenators (140 +/- 19 ng/ml; P less than 0.05) than in plasma from normal subjects (74 +/- 4 ng/ml). The results were not affected by repeated freezing and thawing of the plasma samples.

Production of mouse monoclonal antibodies that detect distinct neoantigenic epitopes on bound C3b and iC3b but not on the corresponding soluble fragments

Polyclonal antibodies raised in rabbits against sodium dodecyl sulphate (SDS)-denatured and reduced human complement factor C3 have in recent studies been shown to lack any reactivity towards native C3 but to react with antigens distinctly expressed by SDS-denatured C3 (C3(D) antigens). These antigens are also neoantigens specific for physiologically bound C3 and appear to be involved in the interaction of C3 with other complement components. The present investigation deals with production of mouse monoclonal antibodies against C3(D) antigens. To accomplish this two different immunization and screening procedures employing C3 preparations of known C3(D) expression were tested. From each group 14 clones were randomly selected and the reactivity of these and of a control group of 14 additional monoclonal anti-human C3 antibody preparations raised against native soluble C3 and C3b, was investigated in ELISA and immunoblotting. The procedure which employed denatured reduced C3 as both immunogen as well as screening antigen was shown to be superior for obtaining anti-C3(D) antibodies. Altogether 16 clones producing antibodies against C3(D) antigens were found. All of them bound to the C3 alpha-chain, 14 to C3c and one to C3d, and eight monoclonal antibodies specific for neoantigens of C3(D) type on bound C3b and/or iC3b were obtained. The majority of these detected neoantigenic epitopes in the 25,000 N-terminal fragment of the C3 alpha-chain specifically exposed by bound iC3b, but one monoclonal antibody was specific for the 36,000 C-terminal alpha-chain fragment and for both bound C3b and iC3b.