M. Dhamrin

Inter-laboratory study of eddy-current measurement of excess-carrier recombination lifetime

Excess-carrier recombination lifetime is a key parameter in silicon solar cell design and production. With the vast international use and recent standardization (SEMI PV13) of eddy-current wafer and brick silicon lifetime test instruments, it is important to quantify the inter- and intra-laboratory repeatability. This paper presents results of an international inter-laboratory study conducted with 24 participants to determine the precision of the SEMI PV13 eddy-current carrier lifetime measurement test method. Overall, the carrier recombination lifetime between-laboratory reproducibility was found to be within ±11% for quasi-steady-state (QSS) mode and ±8% for transient mode for wafer samples and within ±4% for bulk samples.

Characterization of the Initial Rapid Decay on Light-Induced Carrier Lifetime and Cell Performance Degradation of Czochralski-Grown Silicon

The rapid initial degradation of Czochralski-grown silicon (Cz-Si) solar cell performance has been investigated. The initial rapid degradation occurs at the beginning of the degradation process and is followed by a second slower degradation. The surface effect due to interface state degradation between the passivation layer and the Si substrate was investigated on several kinds of Cz- and float zone Si (FZ-Si) wafers. Carrier lifetime degradation induced by an illumination for 30 s was observed on every Cz-Si wafer, but no degradation was observed on FZ-Si wafers. Moreover, only the decrease of IR response of a cell was observed as a result of the initial degradation. The results suggest that the degradation occurs in the bulk. The magnitude and decay time of the degradation appear to depend on the wafer resistivity. Defects very similar to boron–oxygen complexes specific to Cz-Si were considered to be responsible. The distinctly small activation energy of 0.19 eV was obtained for the initial degradation, which suggests a fundamentally different defect reaction process. The activation energy of 1.6 eV for the defect annihilation process was obtained for both defects as well.

Light-induced lifetime degradation of commercial multicrystalline silicon wafers

Light-induced lifetime degradation of conventional cast (CAST), electromagnetic cast (EMC) and heat exchanger method (HEM) multicrystalline silicon wafers have been extensively studied. Results show that samples with lower resistivities have high normalized defect concentration compared to samples with higher resistivities due to their higher boron concentrations. Gettered samples with higher lifetimes degrade more rapidly from their initial values within the first 30 min. The normalized defect concentration has been improved by a factor of 2 indicating the effect of P-diffusion and hydrogen passivation. It is clear that the carrier lifetimes of boron-doped EMC, HEM and CAST silicon wafers degrade as CZ silicon wafers. However, EMC and cast fabricated solar cells show a slight degradation of I/sub sc/, V/sub /spl prop// and efficiencies compared to wafer lifetime degradation. The degree of lifetime degradation depends on boron content and crystal quality suggesting the boron-oxygen complex model as a mechanism for lifetime degradation.

Performance Degradation of Czochralski-Grown Silicon Solar Cells by Means of Current Injection

Performance degradation of Czochralski-grown silicon (Cz–Si) solar cells caused by forward bias voltage application has been investigated. Because of the similarity to light-induced degradation, comparative experiments are carried out on the phenomena. Cell performance decay time evaluations reveal that current injection has a weaker effect on the degradation than illumination in the low-injection region. A difference in the energy of injected electrons is considered to be the reason. Degradation in the high injection region appears identical. Jsc–Voc curve analysis that evaluates bulk lifetime degradation identifies the phenomena.

Characteristic Evaluation of SiNx: H Films Passivation Effect on Ga-doped Multi-crystalline Silicon Wafers

This paper presents the effect of silicon nitride (SiNx:H) films formed by plasma-enhanced chemical vapor deposition (PECVD) method on Ga-doped multi-crystalline silicon (mc-Si) wafers including the passivation quality and carrier lifetime improvement after hydrogenation. The FT-IR spectra of SiNx:H films deposited at different SiH4/NH3 gas flow ratios in PECVD are used to calculated the hydrogen concentrations and bond densities of Si-Hn, N-H and Si-N were calculated. Furthermore, the effect of forming gas annealing (FGA) on the effective lifetime of passivated wafers by PECVD is investigated at different temperatures

Performance improvement in simplified processing for screen-printed mc-Si solar cells

The effect of hydrofluoric (HF) acid treatments performed before and after contact formation on the performance of screen-printed solar cells was examined. The use of silicon-oxide-glass (SOG) for junction separation and its required chemical treatments after diffusion were investigated. The required dipping time in HF solution was less than 2 min. The best solar cells were obtained when the contacts were fired in air ambient at 750 /spl deg/ for 4 min. The highest conversion efficiency in simplified solar cell is obtained after a 50-sec dip in HF after contact formation.

Effect of HF Treatment on Hydrogenated Silicon Nitride Anti-reflection Films Quality and Optical Properties

The effect of diluted hydrofluoric (HF) acid treatment on the refractive index, etch rate and chemical composition of hydrogenated silicon nitride (SiNx:H) films is investigated. The hydrogenated silicon nitride (SiNx:H) films are deposited using the direct plasma enhanced chemical vapor deposition (PECVD) on n +p crystalline silicon solar cells before contact screen-printing process. In order to study the optical properties and chemical composition of formed SiNx:H layers, the reflectance and FT-IR spectra are used. Moreover, the printed contact on the deposited SiNx:H films and its cross section are observed by the scanning electron microscopy (SEM) after firing with different firing durations in quartz tube furnace

Hydrogen Plasma Etching Technique for Mono-and Multi-crystalline Silicon Wafers

A new etching technique for crystalline silicon wafers is developed. The etching technique uses hydrogen radicals supplied by hydrogen remote plasma at room temperature with gas pressures of 0.2-0.5 Torr and hydrogen flow rates of 160-180 sccm for 5-60 min. Scanning electron microscope (SEM) images are used to investigate the surface morphology after etching process. Furthermore, the surface reflectances of the etched samples are measured to estimate the optical properties of the etched samples. An excellent optical properties of the etched surfaces are found where low surface reflectance below 2% are realized at the wavelength regions between 500-900 nm. In addition, the technique is applied to chemically textured crystalline silicon wafers to investigate the technique ability of further improving the already textured surfaces. The results show that hydrogen plasma etching technique is very effective to reduce the surface reflectance properties of surfaces textured with alkaline solutions. Furthermore, possibility of applying this technique to multicrystalline silicon wafers has been investigated. The primary results show a small reduction in surface reflectance as for samples etched with hydrogen flow rates of 170 sccm and 180 sccm

Passivation effect of SiN/sub x/:H films formed by microwave remote plasma CVD for P-diffused substrates

Hydrogenated silicon nitride (SiN/sub x/:H) films on the P-diffused and non diffused substrates were deposited by remote plasma-enhanced chemical vapor deposition (RPECVD) to study the passivation effect on recombination lifetimes and obtain the optimized conditions for SiN/sub x/:H deposition. The effective carrier lifetimes were strongly affected by gas ratio, temperature and deposition time conditions. The maximum effective carrier lifetimes in substrates passivated with SiN/sub x/:H layers deposited by SiH/sub 4//NH/sub 3/ ratio of 15/40 exceeded those of chemically passivated (CP) substrates with iodine/ethanol solution. The best thickness of SiN/sub x/:H deposited on non-diffused wafer and the optimized thickness of P-diffused one are different, and the latter is more thicker. The reflection of SiN/sub x/:H single layer was reduced compared with SiO/sub 2/ films and SiN/sub x/:H/SiO/sub 2/ double layers deposited on non-diffused wafers. The effect of forming gas anneal (FGA) on the effective lifetimes at different temperature (600-800 /spl deg/C) were examined. The effective lifetime increased in a short time and degraded with increasing annealing time. Fast degradation mechanism at higher annealing temperatures was observed.

Technical progress of high-quality, Ga-doped multicrystalline silicon wafers and solar cells

Average carrier lifetimes above 400 /spl mu/s are realized after proper P-diffusion and hydrogen passivation on Ga-doped multicrystalline Si wafers cut from a 70 kg ingot where the response to P-diffusion and hydrogen passivation is pronounced. High carrier lifetimes are realized over the whole ingot with minimum values of 20 /spl mu/s in the top of the ingot indicating the possible use of about 85% of the ingot for solar cell production. The effect of resistivity variation on solar cells conversion efficiency is investigated by means of PC-1D simulation. Conversion efficiencies above 15.5% are realized by utilizing more than 80% of the ingot. Efficiencies as high as 16% are realized on wafers with resistivities higher than 5/spl Omega//spl middot/cm demonstrating high conversion efficiency in high-resistivity, p-type multicrystalline silicon wafers.