Marie Syre Wiig

Influence of pre-annealing of printed silver electrodes on ultrafast laser ablation of short thin-film transistor channels on flexible substrates

The cutoff frequency and current from an organic thin-film transistor (OTFT) are strongly dependent on the length and to some extent on the uniformity of the transistor channel. Reducing the channel length can improve the OTFT performance with the increase in the current and frequency. Picosecond laser ablation of the printed Ag electrodes, compatible with roll-to-roll fabrication, has been investigated. The ablation threshold was found to be similar for the laser wavelengths tested: 515 nm and 1030 nm. Short transistor channels could be opened both after light annealing at 70 °C and after annealing at 140 °C. The channels in the lightly cured films had a significantly less scale formation, which is critical for avoiding shunts in the device. By moving from bottom electrodes fully defined by printing to the bottom electrodes where the transistor channel is opened by the laser, the channel length could be reduced from 40 μm to less than 5 μm.

Identifying recombination parameters by injection-dependent lifetime spectroscopy on mc-silicon based on photoluminescence imaging

The minority carrier lifetime is a crucial material parameter in silicon (Si) wafers for use in solar cell applications, and precise measurements of carrier lifetime as a function of the excess carrier concentration (injection level) is of high importance. In this paper we present a method for extracting injection-dependent lifetime data with high spatial resolution, without the need for advanced time-resolved camera detection systems. This enables investigations of single grains, grain boundaries and structural defects in wafers with spatially non-uniform lifetime, such as high performance multicrystalline Si wafers. The local injection dependent lifetime curves are constructed from a series of photoluminescence images acquired using different steady state generation rates, carefully calibrated by a secondary quasi-steady state photoconductance measurement at a fixed light intensity. The local lifetime has been analyzed by linear parameterization of the Shockley-Read-Hall recombination model and solved for all combinations of defect parameters describing the observed recombination behavior. The recombination parameters found to dominate at high injection corresponds well with published recombination parameters due to Cri.

Temperature coefficients in compensated silicon solar cells investigated by temperature dependent lifetime measurements and numerical device simulation

Silicon solar modules typically operate at a higher temperature than the 25 °C used for standard testing, and the temperature coefficient (TC) therefore might have a significant impact on the field performance. In this paper the temperature dependent behavior of compensated Si solar cells has been simulated using PC1Dmod6.2, using a combination of physical models which include the effect of both temperature and compensation doping. The simulations were based on experimental input measured on two high performance multicrystalline ingots of similar resistivity of ∼1.3 Ωcm, as well as one ingot with a resistivity of 0.5 Ωcm. Two of the ingots are produced using Elkem Solar Silicon (ESS®), a compensated Si feedstock made using a metallurgical purification route, and the third is made from non-compensated reference material. Dopant concentrations as a function of height in the ingot were determined using a combination of experimental resistivity data, simulations and the Scheil equation. Temperature dependent lifetime images, measured on etched and passivated wafers after relevant solar cell processing steps were also acquired at different heights and used as input to the simulations. Taking all this into account, the simulated TC in the efficiency were found to be similar for the two 1.3 Ωcm ingots and slightly higher (less negative) in the 0.5 Ωcm ingot, mostly caused by differences in the TC of the short circuit current and fill factor. We find a reasonable agreement between the simulated and experimental TCs, with the main difference being a ∼0.02 %/K more negative TC in the open circuit voltage in the simulated values. This corresponds to only a 6-7% relative deviation from the experimental values, showing the validity of the PC1Dmod model.Silicon solar modules typically operate at a higher temperature than the 25 °C used for standard testing, and the temperature coefficient (TC) therefore might have a significant impact on the field performance. In this paper the temperature dependent behavior of compensated Si solar cells has been simulated using PC1Dmod6.2, using a combination of physical models which include the effect of both temperature and compensation doping. The simulations were based on experimental input measured on two high performance multicrystalline ingots of similar resistivity of ∼1.3 Ωcm, as well as one ingot with a resistivity of 0.5 Ωcm. Two of the ingots are produced using Elkem Solar Silicon (ESS®), a compensated Si feedstock made using a metallurgical purification route, and the third is made from non-compensated reference material. Dopant concentrations as a function of height in the ingot were determined using a combination of experimental resistivity data, simulations and the Scheil equation. Temperature dependent ...