Photoconductive decay lifetime and Suns-Voc diagnostics of efficient heterojunction solar cells
Minority carrier lifetime and Suns-Voc measurements are well-accepted methods for characterization of solar cell devices. We use these methods, with an instrument from Sinton Consulting, as we fabricate and optimize state-of-the-art all hot-wire chemical vapor deposition (HWCVD) silicon heterojunction (SHJ) devices. For double-sided SHJ devices, lifetime measurements were performed immediately after hydrogenated amorphous silicon (a-Si:H) deposition of the front emitter and back base contacts on a Silicon wafer, and also after indium tin oxide (ITO) deposition of transparent conducting oxide contacts. We report results of minority carrier lifetime measurements for double-sided p-type Si heterojunction devices and compare Suns-Voc results to Light I–V measurements on 1-cm2 solar cell devices measured on an AM1.5 calibrated XT-10 solar simulator.
Determination of Surface Recombination Velocities for Thermal Oxide and Amorphous Silicon on Float Zone Silicon
Introduction Recombination at the surface of a silicon solar cell is an important factor in determining the cell efficiency. The descriptive parameter is surface recombination velocity, s. Generally, s increases as the doping of the surface increases, just as the lifetime of carriers within the crystal (τ) generally decreases as the bulk doping increases. Thus, in a comparative study of candidate surface treatments, it is important to choose a silicon surface doping level which is typical of common cell designs. Furthermore, because standard measurement techniques cannot distinguish between recombination at the crystal surface and recombination within the crystal bulk, it is desirable to choose a silicon crystal with high bulk lifetime in order to improve the sensitivity of the technique to surface recombination. In this study, 100 mm diameter float zone (FZ) silicon wafers, double side polished, with a (100) surface and 300 μm thickness were chosen: p-type (boron-doped) nominally 3 Ω-cm and n-type (phosphorus-doped) nominally 1.2 Ω-cm. The primary comparison was made between surfaces passivated with a thermally-grown oxide and those passivated with amorphous silicon deposited by the hot wire method. In addition, the degree of surface passivation associated with the thin chemical oxide created by RCA cleaning was measured, as was that associated with a temporary iodine-methanol treatment.
Assessment of fractures in endodontically treated teeth restored with and without root canal posts using high-resolution cone beam computed tomography
Background Root fractures are a diagnostic challenge for dentists in endodontic treatment. This study aimed to determine the relationship between the characteristics of tooth fractures and the presence of root canal posts in endodontically treated teeth using high-resolution cone beam computed tomography (CBCT). Material and Methods Fifty high-resolution CBCT scans of endodontically treated teeth with a diagnosis of fracture were obtained, of which 30 were from women and 20 were from men. These scans were acquired with three Veraviewepocs 3D units and one 3D Accuitomo 170 unit, with a 40 × 40-mm field of view and 125 μm voxel size. The variables assessed included the type of fracture, extent of fracture, type of retention, post length, cause of endodontic failure, location of the lesion, and time required to detect the fracture (difficulty score). For data analysis, the chi-squared test, Student’s t-test, and multiple linear regression (α <0.05) were used. Results No association was found between the type of fracture and type of retention or between the type of fracture and its extent (P>0.05). On the other hand, the type of fracture significantly influenced the time required for its detection. Additionally, the most difficult plane for detecting the fracture and the difficulty score were associated, with statistically significant results. Conclusions The type of fracture in endodontically treated teeth was not associated with the type of post used for restoration. All of the CBCT systems used to detect tooth fracture showed the same efficiency. Key words:Cone-Beam CT, Tooth Fracture, Root Canal Post.