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(a) Active dopant profiles throughout the cell structure. The background p-type dopant concentration was about 2 × 10 17 cm −3 and the peak phosphorus (blue symbols) doping concentration was ß10 19 cm −3 . (b) Influence of pulse energy/overlap ratio over the doping depth. (c) Influence of pulse length over the doping depth. (d) Influence of repetition rate and pulse overlap over the doping depth.
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We report on the application of laser chemical processing (LCP) to fabricate n-type emitters for polysilicon thin-film solar cells on glass. Sheet resistance values of 2-5 kΩ/□ with a peak phosphorus doping concentration in the range 8 × 1018 -1 × 1019 cm-3 at a shallow doping depth of less than 350 nm are achieved. After dopant activation and a hy...
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... higher sheet resistance is obtained for the same laser fluence, similar pulse overlap, and a longer pulse length. Since the sheet resistance is related to the active dopant den- sity within the samples, the higher sheet resistance is due to the decreased amount of dopants from using a longer pulse length [refer to the active doping profiles in Fig. 2(c)]. In contrast with our previous findings [8], prolonged annealing at the same tem- perature (e.g., 610 °C for 2 h) for this sample structure resulted in a higher sheet resistance. This could be the result of dopant redistribution across the grains and grain boundaries which then lead to an increased sheet ...
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... susceptible to recombination before they are collected at the space charge re- gion. On the other hand, a highly doped emitter layer decreases the short wavelength light response in a solar cell. To assess the active dopant concentration within the samples, ECV mea- surements were performed on a batch of LCP samples annealed at 610 °C for 30 min. Fig. 2(a)-(d) displays the active dopant profiles of the samples processed using the LCP parameters The measurement uncertainty reflects the standard deviation in the measurements. shown in Table I. The blue symbols represent the n-type dopant (phosphorus), while the corresponding red symbols refer to the p-type dopant (boron). From Fig. ...
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... for 30 min. Fig. 2(a)-(d) displays the active dopant profiles of the samples processed using the LCP parameters The measurement uncertainty reflects the standard deviation in the measurements. shown in Table I. The blue symbols represent the n-type dopant (phosphorus), while the corresponding red symbols refer to the p-type dopant (boron). From Fig. 2(a), the background p-type dopant concentration was about 2 × 10 17 cm −3 and the peak doping concentration of the p + layer was about 2 × 10 18 cm −3 . The peak phosphorus doping concentration was close to 10 19 cm −3 . In Fig. 2(b), an increase in pulse energy resulted in a deeper junction depth because a higher amount of energy was ...
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... represent the n-type dopant (phosphorus), while the corresponding red symbols refer to the p-type dopant (boron). From Fig. 2(a), the background p-type dopant concentration was about 2 × 10 17 cm −3 and the peak doping concentration of the p + layer was about 2 × 10 18 cm −3 . The peak phosphorus doping concentration was close to 10 19 cm −3 . In Fig. 2(b), an increase in pulse energy resulted in a deeper junction depth because a higher amount of energy was available, and thus, the melt front moved deeper into the polysil- icon [8] [refer to samples S1 and S2 processed with a laser pulse energy of 14 and 12 μJ, respectively]. On the other hand, an increase in pulse overlap leads to a ...
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... an increase in pulse overlap leads to a deeper junction depth due to a higher number of melt cycles per unit area [refer to samples S2 and S4 processed with a pulse overlap ratio of 80% and 90%, respectively]. However, an increase in pulse energy has a more significant influence over the junction depth, as shown by samples S2 & S1 and S4 & S3. Fig. 2(c) shows how the pulse length affects the active dopant profile. Using a con- stant pulse energy and a longer pulse length, the peak power decreases and melting is achieved at a lower energy threshold [15]. Therefore, the doping depth is shallower (refer to sam- ples S1 and S5 processed with a pulse length of 20 and 40 ns, respectively). ...
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... the doping depth is shallower (refer to sam- ples S1 and S5 processed with a pulse length of 20 and 40 ns, respectively). Even though melting was achieved at a lower en- ergy for longer pulse lengths, S6 was processed with a much higher fluence resulting in significant material damage. This is also reflected in the irregular doping profile. Fig. 2(d) illustrates the doping depth as a function of the repetition rate. In this case, the repetition rate affects both the incident energy and the pulse overlap. It is shown that for the same incident laser energy, a change in pulse overlap [achieved by altering either the chuck speed (e.g., S4) or the repetition rate (e.g., S9)] affects ...
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... inductively coupled plasma source. From Table II, it is observed that a hydrogenation process can further reduce the sheet resistance of the samples to values less than 2 kΩ/ (see Table I for the previous sheet resistance values) due to improved defect annealing and carrier mobility [refer to sample "S2_after hyd" as compared with sample "S2" in Fig. 2(a)]. These values are promising for decreasing the resistive losses of a poly-Si thin-film solar cell. It is known that hydrogenation improves the carrier mobility as it reduces the grain boundary trap state density in poly-Si [19]. From Fig. 2(a), it is observed that sample "S2_after hyd" is characterized by a flat-top doping profile and ...
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... defect annealing and carrier mobility [refer to sample "S2_after hyd" as compared with sample "S2" in Fig. 2(a)]. These values are promising for decreasing the resistive losses of a poly-Si thin-film solar cell. It is known that hydrogenation improves the carrier mobility as it reduces the grain boundary trap state density in poly-Si [19]. From Fig. 2(a), it is observed that sample "S2_after hyd" is characterized by a flat-top doping profile and shows less dopant smearing than conventional nonmetallized solar cells on glass [12]. This makes LCP an attractive technique to fabricate an active layer (either an emitter or a back surface field) for poly-Si thin-film solar cells. ...
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... p-n junction. As a result, the light-generated current and the V oc were relatively low. In order to predict the gain in V oc for a p-n junction located close to the glass side, a simplified model of a 2-μm-thick poly-silicon thin-film solar cell on glass was implemented into the solar cell modeling program PC1D [25]. By using the ECV data from Fig. 2 as the peak doping concentration/profiles of the active layers (i.e., the bulk layer, the emitter, and the back surface field), the model showed that a shift in the location of the p-n junction from the air side to the glass side could result in a V oc gain of about 7 mV. In principle, for a superstrate device, such a p-n junction ...
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... process. A supporting argument is that the effective ideality factor is quite low (about 1.4). Even though S6 displays a similar effective ideality factor, the high fluence during the LCP process causes simultaneous removal of the doped material and introduces sig- nificant material damage. This also resulted in an irregular dop- ing profile [see Fig. 2(c)]. Future work will consist of optimizing the hydrogenation process and measuring the external quantum efficiency and light current-voltage (I-V) for a complete assess- ment of the device properties and performance. Additionally, future studies will identify the dominant structural [e.g., using Raman spectroscopy, TEM, etc.] and ...
