For Silicon based solar cells with high carrier lifetimes, the carrier density at maximum power point sits at injection levels above 5×1015 cm-3 where the intrinsic Auger lifetime represents the next boundary to the overall device performance. Recent work has proposed revised and improved parametrizations for the Auger recombination, however these studies are restricted to room temperature. In this work we experimentally evaluate the Auger recombination and calculate its ambipolar coefficient across a range of temperatures from 303 to 453 K from photoconductance-based lifetime measurements. Results in n-type FZ silicon suggest the Auger coefficient is temperature-independent when temperature-dependent mobility models are used for the lifetime calculation. We also show that the enhancement factors geeh and gehh are the temperature-dependent parameters governing the temperature behavior of the Auger lifetime.

Heterojunction (HJ) crystalline silicon (c‐Si) solar cells outstanding performance relies heavily on the excellent passivation provided by the amorphous Si (a‐Si:H) layer. However, recombination at the a‐Si:H/c‐Si interface can vary over time and become particularly detrimental for HJ modules performance making the full understanding of the recombination mechanisms at play of paramount importance. In this work, the variation of effective lifetime for high‐quality n‐type FZ c‐Si substrates coated with a‐Si:H(i) layer after several processing steps and over a period of 28 months is tracked. The root cause for degradation is identified by experimentally evaluating the surface recombination velocity (SRV) temperature‐ and injection‐dependence before and after degradation has occurred. By applying a model for the recombination at the a‐Si:H/c‐Si interface to temperature‐ and injection‐dependent SRV data, the authors are able to assess the lifetime decay as entirely ascribed to a loss of chemical passivation. Upon re‐annealing the samples, only a partial recovery of lifetime is obtained suggesting that effusion of hydrogen from the a‐Si:H layer has occurred. These results indicate that the usage of a capping layer is needed whereas a thorough engineering of the a‐Si:H(i) layer thickness may be necessary to avoid the loss of performance of a‐Si based heterojunction structures and modules.

Temperature‐ and injection‐dependent lifetime spectroscopy (TIDLS) is extensively used for the characterization of defects in silicon material for photovoltaic applications. By coupling TIDLS measurements with Shockley–Read–Hall recombination models, the most important defects’ parameters can be assessed including the defect energy level Et and the capture cross section ratio k. However, while proving extremely helpful in a variety of studies aiming at the characterization of contaminated silicon, a generalized approach for the analysis of industrially‐relevant material has not yet emerged. In this contribution, we examine in detail the recently introduced defect parameters contour mapping (DPCM) methodology for TIDLS data analysis as a tool for direct visualization of possible lifetime limiting defects. Herein, we showcase the DPCM method's potential by applying it to two representative case studies selected from literature and we demonstrate that, even when data are scarce, invaluable information is obtained in an easy and intuitive way without any a priori assumption needed. We then apply the DPCM method to simulated TIDLS data to evaluate the general characteristics of its response and the optimal conditions for its application. This analysis proves that the temperature dependence of lifetime is the most critical information required toward a really univocal identification of metal impurities.

This paper comprehends a systematic study of the prospects for an unambiguous assessment of the presence of two separate defects in silicon samples analyzed by temperature- and injection-dependent lifetime spectroscopy (LS). A large number of lifetime datasets are generated by simulating the presence of two defects and then fitted to a single-defect lifetime model. We have categorized the outcome in four categories: (i) a low overall fit quality and thus likely a combination of two defects, (ii) a high overall fit quality by dominance of one of the involved defect, (iii) a high overall fit quality because of symmetry effects in the model, and (iv) a high overall fit quality but no clear dominance by either involved defects nor presence of symmetry effects. We show that the presence of two defects can be ascertained through perceiving a low-quality fit to a single-defect model (category (i)), but we also show that a high-quality fit can arise from a combination of two defects (category (iv)). We show that in the case of categories (i) and (iv), it is possible to identify the two original defects through linear parameterization. In the case of (iii), however, the identification of two simultaneously occurring defects is highly ambitious and not practically feasible.

In this work, we are showing that iron (Fe) related defects in mono-silicon have very different recombination characteristics depending on the doping element employed. While the defect characteristics of the Fe in its dissociated state is comparably the same in the materials of investigation, the defect characteristics of the associated state vary considerably. By using, defect parameter contour mapping (DPCM), a newly developed method for analyzing temperature and injection dependent lifetime data, we have for the first time, been able to show that in the case of gallium doping it is the orthorhombic state of the Fe-acceptor complex that is dominating the lifetime.

Gallium (Ga) doped silicon (Si) is becoming a relevant player in solar cell manufacturing thanks to its demonstrated low light-induced degradation, yet little is known about Ga-related recombination centers. In this paper, we study iron (Fe)-related recombination centers in as-grown, high quality, directionally solidified, monocrystalline Ga-doped Si. While no defect states could be detected by deep level transient spectroscopy, lifetime spectroscopy analysis shows that the minority carrier lifetime in as-grown wafers is dominated by low levels of FeGa related defect complexes. FeGa pairs have earlier been shown to occur in two different structural configurations. Herein, we show that in terms of recombination strength, the orthorhombic pair-configuration is dominant over the trigonal pair-configuration for FeGa. Furthermore, the defect energy level in the band gap for the orthorhombic defect center is determined to be EV + 0.09 eV, and the capture cross-section ratio of the same defect center is determined to be 220.

Surface passivation is a critical consideration when designing high-efficiency solar cells. All advanced solar cell structures are based on high quality surface passivation. A key requirement for improving surface passivation quality is to investigate the electrical properties of the dielectric. However, almost all the previous studies were conducted at room temperature (25 C), which deviate from the actual operating condition of solar cells in the field. In this contribution, we investigate the performance of the most commonly used surface passivation layer in the photovoltaic industry – silicon nitride (SiNx) – in the temperature range of 0 C 100 C. Additional measurements, at even higher temperatures (up to 250 C), are used to reveal the temperature dependence of the fundamental properties of this layer.

In this work we show that the high minority carrier lifetime in as-grown Ga-Si wafers is dominated by low levels of iron contamination incorporated during silicon growth. Upon phosphorous diffusion iron is however effectively removed, increasing the bulk carrier lifetime from a few hundred micro-seconds to well above one milli-second. Lifetime spectroscopy in combination with Shockley Read Hall theory was used to determine the concentrations of Fei and FeGa complexes in the course of the FeGa association. Finally, we use the estimated concentrations of FeGa as a function of time of storage in the dark to validate that FeGa association follows the laws of coulombic attraction similar to FeB.

Metal impurities are known to hinder the performance of commercial Si-based solar cells by inducing bulk recombination, increasing leakage current, and causing direct shunting. Recently, a set of photoluminescence (PL) images of neighboring multicrystalline silicon wafers taken from a cell production line at different processing stages has been acquired. Both band-to-band PL and sub-bandgap PL (subPL) images showed various regions with different PL signal intensity. Interestingly, in several of these regions a reversal of the subPL intensity was observed right after the deposition of the antireflective coating. In this paper, we present the results of the synchrotron-based nano-X-ray fluorescence imaging performed in areas characterized by the subPL reversal to evaluate the possible role of metal decoration in this uncommon behavior. Furthermore, the acquisition of a statistically meaningful set of data for samples taken at different stages of the solar cell manufacturing allows us to shine a light on the precipitation and rediffusion mechanisms of metal impurities at these grain boundaries.

The current trend in silicon photovoltaics towards high-quality thin mono-crystalline silicon substrates makes the accurate representation of surface recombination of utmost importance. It has been shown by several authors that an effective way to study detrimental defects in silicon wafers is by means of temperature and injection dependent lifetime spectroscopy (TIDLS) coupled with the Shockley-Read-Hall recombination model. Given its high sensitivity this is an excellent technique to study high lifetime substrates. However, a thorough evaluation of the surface recombination velocity (SRV) dependence on injection level and temperature is vital to the extrapolation of meaningful results regarding the defects contained in the bulk of the material. Here, we present a TIDLS study of a-Si:H(i), a-Si:H(n) and a-Si:H(p) deposited on n-type low-resistivity FZ substrates. We evaluate the impact of every dielectric layer on the total SRV temperature- and injection dependence while demonstrating its fundamental role in τ eff behavior of high-quality Si substrate.

Cu(In,Ga)Se-2 (CIGS) solar cells were characterized in cross section using electron beam induced current (EBIC) and synchrotron based x-ray fluorescence (XRF) measurements. Samples with varying gallium ratios and growth methods were compared. A correlation was observed between the compositional gallium grading profile from XRF and carrier activity seen in EBIC through the thickness of the CIGS layer. Samples with steep back grading showed carrier activity isolated near the CIGS/CdS interface, whereas a more uniform grading resulted in carrier activity seen throughout the absorber layer. 'Notch' grading showed only slight variation in EBIC profile compared to a back graded sample with similar gallium ratios.

Photoluminescence (PL) imaging is a widely accepted tool to characterize the quality of multicrystalline and monocrystalline silicon cells. Recently a set of neighboring multicrystalline silicon wafers taken from a cell production line at different stages of processing have shown an unexpected PL trend. Band-to-band PL (BPL) and sub-bandgap PL (subPL), where collected for the entire silicon wafers. Interestingly, a reversal of the subPL intensity in various regions of the wafer is observed right after the deposition of the anti-reflective coating (ARC). Regions with low subPL intensity before ARC exhibit high subPL intensity afterwards, and the opposite holds true for other regions of the wafer. Some authors have performed high-resolution cathodoluminescence spectroscopy, EBIC and dark lock-in-thermography to elucidate the origin of this phenomenon, In this work we present the results of the nanoscale X-ray fluorescence imaging at the points of subPL reversal to evaluate the role of metal decoration on this uncommon behavior and we complement it with our previous findings on the distribution of impurities during cell processing.

The effect of temperature on the surface passivation of p-type and n-type monocrystalline silicon is evaluated by temperature dependent photoconductance decay (PCD). Wafers with different passivation layers, i.e. a-Si and SiNx are the subject of these studies. A characteristic lifetime increment is observed for p-type samples coated with a-Si(i) when compared to substrates passivated with SiNx, in agreement with previous literature reports. A different behavior is measured for the case of n-type samples, which show comparable lifetimes among samples with different passivation layers. An interesting lifetime increment is also found at high injection levels for n-type substrates coated with a-Si(i).

Light-induced degradation (LID) due to boron-oxygen complex formation seriously diminishes the efficiency of p-type solar cells. The influence of dopants concentration, net doping and oxygen on the degradation process is investigated using a large variety of B and P compensated mc-Si ingots. Our experiments indicate that the trend of LID depends on the amounts of interstitial oxygen [Oi] and total boron [B]. No clear dependence was found on the net doping.