3.8 Cell efficiency potential prediction: single-sided versus double-sided contact passivation

As already indicated in the introduction part, we can determine a practical solar cell efficiency potential of our investigated solar cell structures, adopting either a rear-sideonly passivated contact scheme or a double-sided passivated contact scheme. Using Brendel's model [54], and explicitly considering measured front-side contact resistance and contact recombination parameters (i.e., the combined front-side saturation current density J0, front, combing the contributions from both the non-metallized/passivated regionsJ0, non-metal and from the metallized regionsJ0, metal), it is possible to calculate a practical solar cell efficiency potential as a function of the rear-side passivated contact layer properties, i.e., the rear-side recombination current density J0, rear and the rearside contact resistance Rc, rear of the rear-side passivated solar cell contact. By fixing the front-side J0, front and Rc, front contributions, iso-efficiency contour plots can be calculated as a function of the rear-side J0, rear and the rear-side Rc, rear (thereby generalizing Brendel's model [54]). The goal of the cell efficiency prediction is twofold: (1) to determine if adopting a double-sided passivated contacts scheme is better than the single-sided (rear) passivated contact scheme and (2) to determine if a full-area rearside contacting scheme is better than a bifacial contacting scheme.

Firstly, Figure 24 shows a comparison of solar cells with a rear-side-only passivated contact scheme, comprising a conventional front-side textured surface with a boron-diffused emitter, passivated by a standard AlOx/SiNx double-layer

100 fA cm<sup>2</sup>

relative gain of 0.9%.

through Ag-Al contact.

Si(n<sup>+</sup>

contact scheme, respectively (see Figure 24).

DOI: http://dx.doi.org/10.5772/intechopen.85039

sured to be 0.22 Ω cm<sup>2</sup> and 13.3 mΩ cm2

). Thus, a combined J0, rear value can be determined to be 8.35 and

, respectively. These J0, rear and Rc, rear

)) and a planar rear

) capping layers, the

)

) capping layer will degrade our measured

)). The

100 fA cm<sup>2</sup> in case of a rear-side bifacial contact scheme or a full-area rear-side

Double-Sided Passivated Contacts for Solar Cell Applications: An Industrially Viable Approach…

As discussed in Brendel's paper [54], in case of a rear-side bifacial contact, the recombination current density J0, rear scales with the rear-side contact area fraction, whereas the effective rear-side contact resistance Rc, rear scales inversely with the rear-side contact area fraction. Again, regarding our developed rear-side SiOx/poly-

) contact passivation layers, the contact resistance Rc, rear of our developed tunnel layer passivated contact has been measured explicitly: Based on our dark I–V test structures, as described in the introduction part of this paper and outlined in Figure 1(f), the values for the bifacial and full-area rear-side contacts were mea-

values were then inserted into our calculated iso-efficiency contour plot in Figure 24, allowing a realistic prediction of the efficiency potential for a rear-side passivated contact solar cell in a bifacial or full-area configuration: As can be seen, the practical solar cell efficiency potential of a solar cell, adopting a conventional front-side boron-diffused emitter and a simple full-area rear-side passivated con-

tact, is 22.3%. In case a bifacial contact is deployed, the practical solar cell

surface with a hole-selective passivated contact (thermal-SiOx/poly-Si(p<sup>+</sup>

front surface of these cells is capped by a double-layer anti-reflection/passivation coating (SiOx/SiNx) and assumed to be contacted via screen-printed fire-through Ag contacts. The rear-side hole-selective passivated contacts are assumed to be either contacted by a full-area Ag contact or to be capped by a double-layer antireflection/passivation coating (AlOx/SiNx), forming a screen-printed bifacial fire-

Accordingly, in order to equate the rear-side J0, rear and Rc, rear values for these two different contact schemes, we apply measured values, and we then plot the practical efficiency potential as a function of the quality of the front-side passivated contact (J0, front and Rc, front). The rear-side J0, rear value underneath the holeselective passivated contact region was determined from the symmetrical lifetime test structures mentioned in earlier sections, while the rear-side Rc, rear value was determined using the dark I–V test structures sketched in Figure 1(f) for the fullarea case (using thermal evaporated Ag instead of screen printed Ag) and correspondingly inversely scaled with the contact-area fraction in case of the bifacial

conventional screen-printing pastes were observed to consume the relatively thin poly-Si capping layer, thereby significantly degrading the rear-side J0, metal and Rc, rear values (as reported in the former section). Nonetheless, in order to predict the practical efficiency potential of double-sided passivated contact solar cells, we assume this problem to be solved, i.e., we assume that applying a screen-printed

contact properties only in the same way as we observe it in case of an electronextracting contact. Thus, as a first order of approximation, we assume the same J0, metal values for a metal contacting the hole-selective passivated contact as we measured it in case of a 250-nm-thick screen-printed SiOx/poly-Si(n<sup>+</sup>

electron-selective passivated contact (thermal-SiOx/poly-Si(n<sup>+</sup>

contact. It is to be noted that for our developed poly-Si(p<sup>+</sup>

contact on a hole-extracting poly-Si(p<sup>+</sup>

121

efficiency potential is 22.5%. Using a rear-side bifacial contact instead of a full-area rear-side contact can therefore slightly enhance the solar cell efficiency by a

The corresponding calculation of the practical efficiency potential for doublesided passivated contact solar cells is shown in Figure 25. As discussed in earlier sections, this solar cell concept features an optimized solar cell architecture considering our experimental finding, i.e., featuring a textured front surface with an

#### Figure 24.

Practical solar cell efficiency potential for a rear-side-only passivated contact solar cell (as a function of the quality of the rear-side passivated contact, i.e., its recombination current density J0, rear and its contact resistance Rc, rear), adopting a conventional front-side boron-diffused emitter and a rear-side electron-selective SiOx/poly-Si(n+ ) passivated contact, realized either in a full-area contact configuration or in a bifacial contact configuration. The measured current recombination densities J0, rear and the correspondingly measured contact resistances Rc, rear of our developed rear-side SiOx/poly-Si(n+ ) electron-extracting passivated contacts are inserted within the iso-efficiency plot (blue dot, full-area contact; black square, bifacial contact). The corresponding practical solar cell efficiency potential using our developed SiOx/poly-Si(n<sup>+</sup> ) passivated contacts is 22.3%, if a full-area rear-side contact is deployed, and 22.5%, if a bifacial contact is deployed.

anti-reflection coating and metallized by conventional screen printing (using a firethrough Ag-Al paste). The rear side composes of our developed electron-selective passivated contacts (thermal-SiOx/poly-Si(n+ )), utilizing an experimentally achievable 10-nm-thick poly-Si(n<sup>+</sup> ) layer and either a full-area Ag contact or a bifacial Ag contact with a contact area fraction similar to the front side (6%). For the efficiency potential prediction, a conservative, industrial feasible J0, front value of 131 fA cm<sup>2</sup> and <sup>R</sup>c, front value of 5 m<sup>Ω</sup> cm2 have been used. This corresponds to a J0, front, pass value of 45 fA cm<sup>2</sup> underneath the AlOx/SiNx passivated B-diffused regions [74] and a J0, front, metal value of 1480 fA cm<sup>2</sup> underneath the metal contacts [2, 75, 76], assuming a front-side metal contact area fraction of 6%.

Regarding our developed rear-side SiOx/poly-Si(n<sup>+</sup> ) contact passivation layers, the corresponding properties have been measured explicitly: Utilizing the symmetrical planar lifetime test structures with electron-selective passivated contacts discussed in earlier sections, the single-sided J0, rear, pass values for the as-deposited and for the additionally SiNx-capped samples were measured as 4.5 and 2.5 fA cm<sup>2</sup> , respectively. The recombination current density underneath the metal contact <sup>J</sup>0, rear, metal has been determined separately as 100 fA cm<sup>2</sup> , using intensitydependent PL imaging and our in-house developed Griddler software [77]. Please note that metal contact recombination after industrial screen printing is significantly reduced (more than one order of magnitude) if deploying contact passivation (i.e., comparing a J0, front, metal value of 1480 fA cm<sup>2</sup> to a J0, rear, metal value of

## Double-Sided Passivated Contacts for Solar Cell Applications: An Industrially Viable Approach… DOI: http://dx.doi.org/10.5772/intechopen.85039

100 fA cm<sup>2</sup> ). Thus, a combined J0, rear value can be determined to be 8.35 and 100 fA cm<sup>2</sup> in case of a rear-side bifacial contact scheme or a full-area rear-side contact scheme, respectively (see Figure 24).

As discussed in Brendel's paper [54], in case of a rear-side bifacial contact, the recombination current density J0, rear scales with the rear-side contact area fraction, whereas the effective rear-side contact resistance Rc, rear scales inversely with the rear-side contact area fraction. Again, regarding our developed rear-side SiOx/poly-Si(n<sup>+</sup> ) contact passivation layers, the contact resistance Rc, rear of our developed tunnel layer passivated contact has been measured explicitly: Based on our dark I–V test structures, as described in the introduction part of this paper and outlined in Figure 1(f), the values for the bifacial and full-area rear-side contacts were measured to be 0.22 Ω cm<sup>2</sup> and 13.3 mΩ cm2 , respectively. These J0, rear and Rc, rear values were then inserted into our calculated iso-efficiency contour plot in Figure 24, allowing a realistic prediction of the efficiency potential for a rear-side passivated contact solar cell in a bifacial or full-area configuration: As can be seen, the practical solar cell efficiency potential of a solar cell, adopting a conventional front-side boron-diffused emitter and a simple full-area rear-side passivated contact, is 22.3%. In case a bifacial contact is deployed, the practical solar cell efficiency potential is 22.5%. Using a rear-side bifacial contact instead of a full-area rear-side contact can therefore slightly enhance the solar cell efficiency by a relative gain of 0.9%.

The corresponding calculation of the practical efficiency potential for doublesided passivated contact solar cells is shown in Figure 25. As discussed in earlier sections, this solar cell concept features an optimized solar cell architecture considering our experimental finding, i.e., featuring a textured front surface with an electron-selective passivated contact (thermal-SiOx/poly-Si(n<sup>+</sup> )) and a planar rear surface with a hole-selective passivated contact (thermal-SiOx/poly-Si(p<sup>+</sup> )). The front surface of these cells is capped by a double-layer anti-reflection/passivation coating (SiOx/SiNx) and assumed to be contacted via screen-printed fire-through Ag contacts. The rear-side hole-selective passivated contacts are assumed to be either contacted by a full-area Ag contact or to be capped by a double-layer antireflection/passivation coating (AlOx/SiNx), forming a screen-printed bifacial firethrough Ag-Al contact.

Accordingly, in order to equate the rear-side J0, rear and Rc, rear values for these two different contact schemes, we apply measured values, and we then plot the practical efficiency potential as a function of the quality of the front-side passivated contact (J0, front and Rc, front). The rear-side J0, rear value underneath the holeselective passivated contact region was determined from the symmetrical lifetime test structures mentioned in earlier sections, while the rear-side Rc, rear value was determined using the dark I–V test structures sketched in Figure 1(f) for the fullarea case (using thermal evaporated Ag instead of screen printed Ag) and correspondingly inversely scaled with the contact-area fraction in case of the bifacial contact. It is to be noted that for our developed poly-Si(p<sup>+</sup> ) capping layers, the conventional screen-printing pastes were observed to consume the relatively thin poly-Si capping layer, thereby significantly degrading the rear-side J0, metal and Rc, rear values (as reported in the former section). Nonetheless, in order to predict the practical efficiency potential of double-sided passivated contact solar cells, we assume this problem to be solved, i.e., we assume that applying a screen-printed contact on a hole-extracting poly-Si(p<sup>+</sup> ) capping layer will degrade our measured contact properties only in the same way as we observe it in case of an electronextracting contact. Thus, as a first order of approximation, we assume the same J0, metal values for a metal contacting the hole-selective passivated contact as we measured it in case of a 250-nm-thick screen-printed SiOx/poly-Si(n<sup>+</sup> )

anti-reflection coating and metallized by conventional screen printing (using a firethrough Ag-Al paste). The rear side composes of our developed electron-selective

Practical solar cell efficiency potential for a rear-side-only passivated contact solar cell (as a function of the quality of the rear-side passivated contact, i.e., its recombination current density J0, rear and its contact resistance Rc, rear), adopting a conventional front-side boron-diffused emitter and a rear-side electron-selective SiOx/poly-

) passivated contact, realized either in a full-area contact configuration or in a bifacial contact configuration. The measured current recombination densities J0, rear and the correspondingly measured contact

inserted within the iso-efficiency plot (blue dot, full-area contact; black square, bifacial contact). The

is 22.3%, if a full-area rear-side contact is deployed, and 22.5%, if a bifacial contact is deployed.

corresponding practical solar cell efficiency potential using our developed SiOx/poly-Si(n<sup>+</sup>

the corresponding properties have been measured explicitly: Utilizing the symmetrical planar lifetime test structures with electron-selective passivated contacts discussed in earlier sections, the single-sided J0, rear, pass values for the as-deposited and for the additionally SiNx-capped samples were measured as 4.5 and 2.5 fA cm<sup>2</sup>

respectively. The recombination current density underneath the metal contact

dependent PL imaging and our in-house developed Griddler software [77]. Please note that metal contact recombination after industrial screen printing is significantly reduced (more than one order of magnitude) if deploying contact passivation (i.e., comparing a J0, front, metal value of 1480 fA cm<sup>2</sup> to a J0, rear, metal value of

Ag contact with a contact area fraction similar to the front side (6%). For the efficiency potential prediction, a conservative, industrial feasible J0, front value of 131 fA cm<sup>2</sup> and <sup>R</sup>c, front value of 5 m<sup>Ω</sup> cm2 have been used. This corresponds to a J0, front, pass value of 45 fA cm<sup>2</sup> underneath the AlOx/SiNx passivated B-diffused regions [74] and a J0, front, metal value of 1480 fA cm<sup>2</sup> underneath the metal contacts [2, 75, 76], assuming a front-side metal contact area fraction of 6%.

)), utilizing an experimentally achiev-

) passivated contacts

) electron-extracting passivated contacts are

) contact passivation layers,

, using intensity-

,

) layer and either a full-area Ag contact or a bifacial

passivated contacts (thermal-SiOx/poly-Si(n+

resistances Rc, rear of our developed rear-side SiOx/poly-Si(n+

Regarding our developed rear-side SiOx/poly-Si(n<sup>+</sup>

<sup>J</sup>0, rear, metal has been determined separately as 100 fA cm<sup>2</sup>

able 10-nm-thick poly-Si(n<sup>+</sup>

Figure 24.

Silicon Materials

Si(n+

120

contact solar cell. To give an example, a bifacial double-sided passivated contact solar cell exhibits much lower total surface recombination (J0, front + J0, rear values

Double-Sided Passivated Contacts for Solar Cell Applications: An Industrially Viable Approach…

surface passivation should also directly translate to higher cell efficiencies, which is clearly shown comparing Figure 25 to Figure 24. According to Figure 25, a double-sided passivated contact solar cell, using our developed SiOx/poly-Si(n<sup>+</sup>

potential of 22.3 and 23.2%, respectively, using full-area or bifacial rear-side contacts. To recap, the corresponding practical efficiency potential in case of a rearside-only passivated contact solar cell was 22.3 and 22.5%, respectively. Thus, in case of adopting a bifacial metallization scheme, a double-sided passivated contact solar cell is able to clearly outperform a rear-side-only passivated contact solar cell (practical efficiency potential of 23.2% as compared to 22.5%, using our developed

Again, the bifacial contact scheme appears more advantageous than deploying full-area rear-side contacts, exhibiting a significant 0.9% absolute (4% relative) increase in practical efficiency potential (analyzing double-sided passivated contact solar cells). If we compare bifacial silicon solar cells with a doublesided passivated contact scheme to rear-side-only passivated contact scheme, a respectable gain in cell efficiency by 0.7% absolute (3% relative) is attainable. Interestingly, if we compare silicon solar cells which utilized full-area rear-side metal contacts, the practical cell efficiency potential for the double-sided passivated contact cell appears to be comparable to the rear-side-only passivated contact cell (both efficiency potentials are in the range of 22.3%). Given comparable J0, rear, Rc, rear, and Rc, front values between the two schemes, it seems to indicate that a solar cell adopting a full-area rear-side passivated contact scheme exhibits a low sensitivity of the J0, front values on the potential cell efficiency over a range of 12–131 fA cm<sup>2</sup> (i.e., the full-area rear-side contact is then limiting the cell efficiency). However, when bifacial contacts are considered, the performance gain by applying additional front-side passivation is substantial. This can be mainly attributed to the reduced recombination underneath the front-side solar cell contacts (further suppressing front-side recombination from 131 to 12 fA cm<sup>2</sup>

while maintaining a low front-side contact resistance, i.e., comparing

One suggestion to further improve the cell efficiency is to utilize laserassisted local openings into the rear-side dielectrics (as demonstrated in Figure 22)

To summarize, the net surface passivation quality on both the solar cell front-side and rear-side can be significantly improved by incorporating our inhouse developed carrier-selective passivated contacts. A double-sided passivated contact scheme is predicted to deliver a 3% relative improvement of solar cell performance, as compared to a rear-side-only passivated contact scheme. Using a rear-side-only passivated contact scheme, i.e., deploying our in-house developed

screen printing, we have realized a solar cell efficiency of 21.7% (exhibiting a practical efficiency potential of 22.5%, using our standard boron-diffused frontside contact). The still prevailing challenge is to realize an industrial feasible

i.e., to develop suitable pastes to contact p-doped poly-Si by means of

metallization scheme on hole-extracting poly-Si(p<sup>+</sup>

) passivated contact layers and applying conventional bifacial

) contact passivation layers,

and apply a full-area non-fire-through metal contact, which is expected to improve the rear interface reflectance and the corresponding collectable

) than a bifacial rear-side-only passivated contact solar cell

) passivated contacts, exhibits a practical solar cell efficiency

), which is 4 times lower. The improved

)

of 32.7 fA cm<sup>2</sup>

and SiOx/poly-Si(p<sup>+</sup>

contact passivation layers).

5–13 mΩ cm<sup>2</sup>

photocurrents.

SiOx/poly-Si(n<sup>+</sup>

screen printing.

123

).

(J0, front + J0, rear values of 139.5 fA cm<sup>2</sup>

DOI: http://dx.doi.org/10.5772/intechopen.85039

#### Figure 25.

Practical solar cell efficiency potential for a double-sided passivated contact solar cell (as a function of the quality of the rear-side hole-extracting passivated contact, i.e., its recombination current density J0, rear and its contact resistance Rc, rear), adopting an ultrathin 10-nm electron-selective SiOx/poly-Si(n+ ) passivated contact on the textured front-side and a hole-selective SiOx/poly-Si(p<sup>+</sup> ) passivated contact on the planar rear-side, realized either in a full-area contact configuration or in a bifacial contact configuration. The adopted J0, metal, J0, non-metal, and Rc values are based on own measurements (see text). The estimated current recombination density J0, rear and the correspondingly estimated contact resistance Rc, rear of our developed hole-extracting passivated contact (assuming that the observed screen-printing issues have been solved) are inserted within the iso-efficiency plot (blue dot, full-area contact; black square, bifacial contact). The corresponding practical solar cell efficiency potential using our developed electron- and hole-extracting SiOx/poly-Si passivated contacts is 22.3%, if a full-area rear-side contact is deployed, and 23.2%, if a bifacial contact is deployed.

electron-selective passivated contact (100 fA cm<sup>2</sup> ), and we utilized measured Rc, rear values which we extracted using a thermal evaporated Ag contact instead of a screen-printed contacts, i.e., obtaining Rc, rear values of 0.225 and 13.5 mΩ cm2 for the bifacial and full-area rear-contacts, respectively. The corresponding practical efficiency potential, as a function of the quality of the rear-side hole-extracting passivated contact (J0, rear and Rc, rear), is shown in Figure 25.

Comparing a front-side electron-extracting passivated contact to a conventionally applied front-side hole-extracting diffused contact (front-side boron-diffused emitter, passivated with ALOx/SiNx and metallized by bifacial screen printing) greatly improves the front surface passivation quality, reducing the J0, front value from 131 to 12 fA cm<sup>2</sup> , respectively. This can be (1) attributed to the excellent passivation quality of the developed electron-selective passivated contacts itself (6.65 fA cm<sup>2</sup> on a textured silicon surface), which cannot be attained by conventional boron diffusion and AlOx/SiNx capping (45 fA cm<sup>2</sup> ). Furthermore, the metal front-side contacts are now passivated (assuming <sup>J</sup>0, metal, 100 fA cm<sup>2</sup> , after industrial screen printing, as measured on 250-nm-thick poly-Si(n<sup>+</sup> ) capping layers) instead of directly touching the doped silicon wafer (J0, metal, 1480 fA cm<sup>2</sup> ). Therefore, a double-sided passivated contact solar cell has a good potential to obtain higher VOC values at the cell level than a rear-side-only passivated

Double-Sided Passivated Contacts for Solar Cell Applications: An Industrially Viable Approach… DOI: http://dx.doi.org/10.5772/intechopen.85039

contact solar cell. To give an example, a bifacial double-sided passivated contact solar cell exhibits much lower total surface recombination (J0, front + J0, rear values of 32.7 fA cm<sup>2</sup> ) than a bifacial rear-side-only passivated contact solar cell (J0, front + J0, rear values of 139.5 fA cm<sup>2</sup> ), which is 4 times lower. The improved surface passivation should also directly translate to higher cell efficiencies, which is clearly shown comparing Figure 25 to Figure 24. According to Figure 25, a double-sided passivated contact solar cell, using our developed SiOx/poly-Si(n<sup>+</sup> ) and SiOx/poly-Si(p<sup>+</sup> ) passivated contacts, exhibits a practical solar cell efficiency potential of 22.3 and 23.2%, respectively, using full-area or bifacial rear-side contacts. To recap, the corresponding practical efficiency potential in case of a rearside-only passivated contact solar cell was 22.3 and 22.5%, respectively. Thus, in case of adopting a bifacial metallization scheme, a double-sided passivated contact solar cell is able to clearly outperform a rear-side-only passivated contact solar cell (practical efficiency potential of 23.2% as compared to 22.5%, using our developed contact passivation layers).

Again, the bifacial contact scheme appears more advantageous than deploying full-area rear-side contacts, exhibiting a significant 0.9% absolute (4% relative) increase in practical efficiency potential (analyzing double-sided passivated contact solar cells). If we compare bifacial silicon solar cells with a doublesided passivated contact scheme to rear-side-only passivated contact scheme, a respectable gain in cell efficiency by 0.7% absolute (3% relative) is attainable. Interestingly, if we compare silicon solar cells which utilized full-area rear-side metal contacts, the practical cell efficiency potential for the double-sided passivated contact cell appears to be comparable to the rear-side-only passivated contact cell (both efficiency potentials are in the range of 22.3%). Given comparable J0, rear, Rc, rear, and Rc, front values between the two schemes, it seems to indicate that a solar cell adopting a full-area rear-side passivated contact scheme exhibits a low sensitivity of the J0, front values on the potential cell efficiency over a range of 12–131 fA cm<sup>2</sup> (i.e., the full-area rear-side contact is then limiting the cell efficiency). However, when bifacial contacts are considered, the performance gain by applying additional front-side passivation is substantial. This can be mainly attributed to the reduced recombination underneath the front-side solar cell contacts (further suppressing front-side recombination from 131 to 12 fA cm<sup>2</sup> while maintaining a low front-side contact resistance, i.e., comparing 5–13 mΩ cm<sup>2</sup> ).

One suggestion to further improve the cell efficiency is to utilize laserassisted local openings into the rear-side dielectrics (as demonstrated in Figure 22) and apply a full-area non-fire-through metal contact, which is expected to improve the rear interface reflectance and the corresponding collectable photocurrents.

To summarize, the net surface passivation quality on both the solar cell front-side and rear-side can be significantly improved by incorporating our inhouse developed carrier-selective passivated contacts. A double-sided passivated contact scheme is predicted to deliver a 3% relative improvement of solar cell performance, as compared to a rear-side-only passivated contact scheme. Using a rear-side-only passivated contact scheme, i.e., deploying our in-house developed SiOx/poly-Si(n<sup>+</sup> ) passivated contact layers and applying conventional bifacial screen printing, we have realized a solar cell efficiency of 21.7% (exhibiting a practical efficiency potential of 22.5%, using our standard boron-diffused frontside contact). The still prevailing challenge is to realize an industrial feasible metallization scheme on hole-extracting poly-Si(p<sup>+</sup> ) contact passivation layers, i.e., to develop suitable pastes to contact p-doped poly-Si by means of screen printing.

electron-selective passivated contact (100 fA cm<sup>2</sup>

on the textured front-side and a hole-selective SiOx/poly-Si(p<sup>+</sup>

from 131 to 12 fA cm<sup>2</sup>

fA cm<sup>2</sup>

122

Figure 25.

Silicon Materials

passivated contact (J0, rear and Rc, rear), is shown in Figure 25.

tional boron diffusion and AlOx/SiNx capping (45 fA cm<sup>2</sup>

Rc, rear values which we extracted using a thermal evaporated Ag contact instead of a screen-printed contacts, i.e., obtaining Rc, rear values of 0.225 and 13.5 mΩ cm2 for the bifacial and full-area rear-contacts, respectively. The corresponding practical efficiency potential, as a function of the quality of the rear-side hole-extracting

Practical solar cell efficiency potential for a double-sided passivated contact solar cell (as a function of the quality of the rear-side hole-extracting passivated contact, i.e., its recombination current density J0, rear and its

realized either in a full-area contact configuration or in a bifacial contact configuration. The adopted J0, metal, J0, non-metal, and Rc values are based on own measurements (see text). The estimated current recombination density J0, rear and the correspondingly estimated contact resistance Rc, rear of our developed hole-extracting passivated contact (assuming that the observed screen-printing issues have been solved) are inserted within the iso-efficiency plot (blue dot, full-area contact; black square, bifacial contact). The corresponding practical solar cell efficiency potential using our developed electron- and hole-extracting SiOx/poly-Si passivated contacts is

contact resistance Rc, rear), adopting an ultrathin 10-nm electron-selective SiOx/poly-Si(n+

22.3%, if a full-area rear-side contact is deployed, and 23.2%, if a bifacial contact is deployed.

Comparing a front-side electron-extracting passivated contact to a conventionally applied front-side hole-extracting diffused contact (front-side boron-diffused emitter, passivated with ALOx/SiNx and metallized by bifacial screen printing) greatly improves the front surface passivation quality, reducing the J0, front value

passivation quality of the developed electron-selective passivated contacts itself (6.65 fA cm<sup>2</sup> on a textured silicon surface), which cannot be attained by conven-

metal front-side contacts are now passivated (assuming <sup>J</sup>0, metal, 100 fA cm<sup>2</sup>

tial to obtain higher VOC values at the cell level than a rear-side-only passivated

). Therefore, a double-sided passivated contact solar cell has a good poten-

after industrial screen printing, as measured on 250-nm-thick poly-Si(n<sup>+</sup>

layers) instead of directly touching the doped silicon wafer (J0, metal, 1480

, respectively. This can be (1) attributed to the excellent

), and we utilized measured

) passivated contact on the planar rear-side,

). Furthermore, the

,

) capping

) passivated contact
