The versatility of passivating carrier‐selective silicon thin films for diverse high‐efficiency screen‐printed heterojunction‐based solar cells

Abstract

Providing state-of-the-art surface passivation and the required carrier selectivity for both contacts, hydrogenated amorphous silicon thin films are the key components of silicon heterojunction (SHJ) solar cells. After intensive optimization of these layers for standard front and back contacted (FBC) n-type cells, high surface passivation levels were achieved on cell precursors, demonstrated by minority carrier lifetimes exceeding 18 ms on float-zone (FZ) and 11 ms on Czochralski (Cz) c-Si wafers. The application of these very same layers on cheaper and commercially available Cz ptype wafers resulted in similar passivation quality, with lifetimes above 10 ms as well.Large-area industrial bifacial FBC SHJ cells processed on wafers taken along the full length of a high-resistivity Cz p-type ingot showed efficiencies in the 22.5% to 23% range, significantly higher than previously reported results on such substrates and on par with their n-type counterparts. Best efficiencies on large-area monofacial devices (>220 cm 2 ) are 23.6% on Cz p-type and 24.4% on Cz n-type, similar to certified results obtained on lab-scale cells (4 cm 2 ), 23.76% on FZ p-type and 24.21% on FZ n-type. Notably, no specific adaptation of the reference n-type cell process was necessary to achieve these results on p-type material. Additionally, a 25% certified efficiency has been obtained on medium-sized (25 cm 2 ) interdigitated backcontacted SHJ cells, featuring the same passivation layers developed for FBC devices.These results illustrate the versatility of the SHJ technology for various highefficiency screen-printed solar cell configurations and show possible ways to improve its competitiveness on the global photovoltaic market.

Large‐Area Boron‐Doped 1.6 Ω cm p‐Type Czochralski Silicon Heterojunction Solar Cells with a Stable Open‐Circuit Voltage of 736 mV and Efficiency of 22.0%

“…Substantial progress on high-efficiency p-type silicon solar cells has recently been made, such as work by Haase et al with an interdigitated back contact solar cell featuring tunnel oxide-doped polycrystalline silicon contacts with efficiency of 26.1% (float-zone [FZ] silicon with resistivity of 100 Ω cm and V OC of 727 mV) [9] and by Descoeudres et al on a SHJ structure with efficiencies of 23.8% (FZ silicon with V OC of 723 mV) and 23.6% (Cz silicon with V OC of 740 mV). [10] While the V OC of the champion p-type Cz SHJ solar cell from Descoeudres et al is comparable with the V OC of the world-record n-type SHJ solar cell from Yoshikawa et al, the fill factor (FF) of the p-type device is 4.1% abs lower. However, the average efficiency of larger batches of identically processed n-type and gettered p-type SHJ solar cells was at the same level, [10] suggesting that p-type SHJ solar cells may be able to achieve the same average efficiencies as n-type SHJ solar cells in production.…”

“…[10] While the V OC of the champion p-type Cz SHJ solar cell from Descoeudres et al is comparable with the V OC of the world-record n-type SHJ solar cell from Yoshikawa et al, the fill factor (FF) of the p-type device is 4.1% abs lower. However, the average efficiency of larger batches of identically processed n-type and gettered p-type SHJ solar cells was at the same level, [10] suggesting that p-type SHJ solar cells may be able to achieve the same average efficiencies as n-type SHJ solar cells in production. It is important to note that with the addition of a dedicated gettering step to improve material quality, Descoeudres et al observed an efficiency gain of %0.2% abs in batches of p-type SHJ solar cells.…”

“…It is important to note that with the addition of a dedicated gettering step to improve material quality, Descoeudres et al observed an efficiency gain of %0.2% abs in batches of p-type SHJ solar cells. [10] In previous studies, we have also demonstrated the role of gettering in increasing the lifetime of p-type Cz silicon, [5,11,12] which translated to a %1% abs increase in the efficiency of SHJ solar cells. These results together indicate the need for gettering as a defect-engineering process to enhance the quality of p-type silicon wafers for SHJ solar cells applications.…”

“…This result is in agreement with the literature, confirming that while the key feature of SHJ solar cells of enabling high V OC is preserved on p-type silicon, the low τ eff at low injection (τ eff,low ) results in reduced FF. [24] Although the use of AHP on the finished p-type SHJ solar cells enhanced the FF, the average FF of 74.8% (G þ AHP) is still a limiting factor, approximately 6% abs lower than the recent p-type Cz SHJ solar cell results from Descoeudres et al [10] It is expected that this is due to a surface-related effect rather than a bulk effect, reducing the lifetime at low injection. [24] Olibet et al suggested that the lower τ eff,low on p-type than on n-type is due to the discrepancy between the capture cross section for electrons Table 1.…”

“…However, to date, little work has been done investigating LID in p-type SHJ solar cells. [11,20] For example, LID testing was not performed for the record cells from Descoeudres et al, although it was noted such wafers are likely to suffer from bulk degradation due to light-induced effects, [10] albeit with presumably a reduced total defect concentration due to the high wafer resistivity (6 Ω cm after gettering and the annihilation of thermal donors). In our recent work, we fabricated p-type SHJ solar cells that were susceptible to an efficiency degradation of 0.9% abs (4.7% rel ); [20] however, the degradation could be greatly reduced to 0.2% abs (1% rel ) using an advanced hydrogenation process.…”