Perimeter Recombination in 25%-Efficient IBC Solar Cells With Passivating POLO Contacts for Both Polarities

Thin crystalline silicon (c‐Si) solar cells are highly attractive for realizing light‐weight and flexible wafer‐based solar cells as well as for reducing the material cost. Silicon heterojunction (SHJ) architecture using hydrogenated amorphous silicon (a‐Si:H) is suitable for realizing very thin c‐Si cells, because of its capability of excellent surface passivation. In this work, the potential of very thin c‐Si solar cells is examined by characterizing SHJ solar cells with a wide range of thicknesses from 50 to 400 μm. A trade‐off between the open‐circuit voltage (VOC) and the short circuit current density (JSC) against wafer thickness is clearly observed in these SHJ cells, whereas a decrease in fill factor (FF) is found for thin SHJ cells below 80 μm. The loss analysis for the thin SHJ cells with numerical simulation clarifies that the infrared parasitic absorption loss due to the supporting layers is enhanced for thinner wafers, which limits the JSC in the thin SHJ cells. In addition, it is confirmed that the FF is more sensitive to surface recombination than the VOC, and this tendency becomes more pronounced with the decrease in the wafer thickness. A high efficiency of 22% is achieved in a SHJ solar cell with a thickness of only 46 μm, demonstrating a high potential for flexible high‐efficiency c‐Si solar cells.

Section: Solar Cell Resultsmentioning

confidence: 61%

Section: Resultsmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Potential of very thin and high‐efficiency silicon heterojunction solar cells

Sai

Oku

Satô

et al. 2019

“…In this state, the cell is measured both with and without a masked perimeter region (as well passivated as the active cell region) in contrast to the first two measurements, which are done without a mask. The comparison of the implied pseudo‐ I ‐ V parameters of the cell with a masked and unmasked perimeter region yields the efficiency loss due to perimeter recombination …”

Section: Methodsmentioning

confidence: 99%

“…The comparison of the implied pseudo-I-V parameters of the cell with a masked and unmasked perimeter region yields the efficiency loss due to perimeter recombination. 15 To calculate the implied pseudo-I-V parameters from the lifetime measurements, we have to asses a value for the short-circuit current density. Nevertheless, we have to assume that a decrease of J SC is occurring during the process, which is however difficult to determine.…”

Section: Measurementsmentioning

confidence: 99%

26.1%‐efficient POLO‐IBC cells: Quantification of electrical and optical loss mechanisms

Hollemann

Haase

Schäfer

et al. 2019

Self Cite

We present experimental results for interdigitated back contacted (IBC) solar cells with passivating POLO contacts for both polarities with a nominal intrinsic poly‐Si region between them. We reach efficiencies of 26.1% and 24.9% on a 1.3 Ω cm and 80 Ω cm p‐type FZ wafer and 24.6% on a 2 Ω cm n‐type Cz wafer, respectively. The initially measured implied efficiency potentials of the cells after passivating the surfaces are very similar, namely, 26.8%, 26.8%, and 26.4%, respectively. We attribute the difference between the efficiency potential and the final current‐voltage measurement to degradation, perimeter, and series and shunt resistance losses, which we quantify by lifetime measurements. With these measurements in combination with a finite element simulation, we determine the surface recombination velocity in the nominal intrinsic poly‐Si region to be in the range from 13 to 21 cm s−1. Using the same approach, we analyze the increase of the front surface recombination velocity during cell processing from 2 to 10 cm s−1 for the 1.3 Ω cm and from 0.5 to 2.3 cm s−1 for the 80 Ω cm. This leads to the fact that cells fabricated on lowly doped bulk material are more vulnerable to a process‐induced degradation of the surface passivation quality. We further determine the theoretical limits of the cells by firstly idealizing the recombination (28% for 1.3 Ω cm and 28.2% for 80 Ω cm) and secondly also idealizing the optics of the solar cells (29.4% and 29.5%).

Nanocrystalline‐silicon hole contact layers enabling efficiency improvement of silicon heterojunction solar cells: Impact of nanostructure evolution on solar cell performance

Umishio

Sai

Koida

et al. 2020

Hydrogenated amorphous silicon (a‐Si:H) is a key enabler in high‐efficiency crystalline silicon solar cells known as the silicon heterojunction technology. Although efforts have been devoted to replacing doped a‐Si:H contact layer by hydrogenated nanocrystalline silicon (nc‐Si:H) to take advantage of its superior optoelectrical properties, it is still unclear whether the nc‐Si:H outperforms the a‐Si:H at the high efficiency level. Here, we show that boron‐doped (p)nc‐Si:H prepared by plasma‐enhanced chemical vapor deposition (PECVD) acts as an efficient hole contact layer, providing not only a mitigation of the parasitic absorption loss but also improvements in passivation and electrical contact properties. This results in an efficiency increase by 0.3%–0.6% absolute compared to the reference cell with the (p)a‐Si:H, and a best cell efficiency of 23.54%. We find that the critical thickness of the (p)nc‐Si:H layers required for gaining high efficiency (tc ~ 15–30 nm) is a factor of 3–6 greater than that of the (p)a‐Si:H. UV Raman spectroscopy and electrical conductivity measurements reveal that the tc of the (p)nc‐Si:H is associated with the layer growth needing for the surface coalescence of nanocrystals, determining the hole selectivity and the contact resistivity at the electrode/(p)nc‐Si:H interface. Our results suggest that such nanostructure evolution can be hastened by using a very‐high‐frequency PECVD process.