Stable Dopant-Free Asymmetric Heterocontact Silicon Solar Cells with Efficiencies above 20%

Bullock, James; Wan, Yimao; Xu, Zhaoran; Essig, Stephanie; Hettick, Mark; Wang, Hanchen; Ji, Wenbo; Boccard, Mathieu; Cuevas, Andrés; Ballif, Christophe; Javey, Ali

doi:10.1021/acsenergylett.7b01279

Cited by 177 publications

(188 citation statements)

References 35 publications

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“…[1][2][3][4][5][6][7] Such an approach has potential benefits over conventional heavily doped direct-metallization approaches, including lower processing temperatures, simpler contact formation, and the removal of fundamental limitations, such as Auger recombination and free carrier absorption. For example, materials such as metal oxides, nitrides, and fluorides have been demonstrated to form electron and hole selective interfaces when applied to c-Si.…”

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confidence: 99%

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

Bullock

Wan

Hettick

et al. 2019

Advanced Energy Materials

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improving the performance of this technology. For example, materials such as metal oxides, nitrides, and fluorides have been demonstrated to form electron and hole selective interfaces when applied to c-Si. [1][2][3][4][5][6][7] Such an approach has potential benefits over conventional heavily doped direct-metallization approaches, including lower processing temperatures, simpler contact formation, and the removal of fundamental limitations, such as Auger recombination and free carrier absorption. [8,9] In addition, the unique interface properties of some metal compound/c-Si interfaces have even enabled novel solar cell architectures, for example, n-type c-Si cells with undoped partial rear contacts (PRCs). [10,11] This specific architecture utilizes a near-ideal surface passivation layer, such as hydrogenated silicon nitride SiN x , [12] to cover the vast majority of the rear surface which can greatly reduce the average surface recombination factor J 0 and increase the rear reflection. Only a small percentage of the area is contacted, typically < 5%, where electrons flow to be collected. An n-type undoped PRC cell structure was not previously attainable due to the tendency of n-type c-Si to form an interface potential barrier under direct metallization, which resulted in prohibitively high contact resistivity ρ c . The first successful demonstration of this cell came after a breakthrough in low resistance interfaces to n-type c-Si with a low work function LiF x /Al electrode. This contact was used to fabricate an undoped PRC cell attaining an efficiency of 20.6% with a PRC covering only ≈1% of the rear surface. [11] The next evolutionary step in this cell structure was the integration of a passivation layer at the PRC interface. This came with the introduction of a TiO x /Ca/Al contact, [10] which was found to provide both reduced surface recombination and low contact resistivity, enabling an efficiency of 21.8%. Following on from these early developments, there exist three major avenues to easily improve the electron PRC: i) reduction in the PRC interface recombination and resistivity; ii) increase in the PRC material's stability to thermal stressors; and iii) increasing the rear surface reflectivity via appropriate choice of PRC materials.This article introduces the next in this family of carrier selective interfaces, which targets the abovementioned three issues. To address this a TiO x /LiF x /Al heterocontact is developed and integrated into a PRC cell shown in Figure 1a. The

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confidence: 99%

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

Bullock

Wan

Hettick

et al. 2019

Advanced Energy Materials

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123

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“…Reducing optical and electrical losses is crucial to increase the power conversion efficiency (PCE) of solar cells; therefore, highly doped regions are aimed to be replaced with dopant‐free carrier selective contacts, that benefit simple deposition methods and less intrinsic losses. Solar cell designs based on dopant free layers, the dopant‐free asymmetric silicon heterostructure (DASH) solar cells, have attained impressive efficiency values exceeding 20% …”

Section: Introductionmentioning

confidence: 99%

“…Solar cell designs based on dopant free layers, the dopant-free asymmetric silicon heterostructure (DASH) solar cells, have attained impressive efficiency values exceeding 20%. 6,7 In order to be used in PV c-Si based cells, TCEs should have high transparency in the 300 to 1200-nm wavelength range, while also having low resistivity to enable large area carrier transport without significant resistive losses. In addition, a good TCE is expected to (a) have compatible work function matching with the adjacent layers to get low contact resistance, 8 (b) be suitable for uniform deposition using conventional methods, (c) enhance the light coupling into the active layer of the solar cell, 9,10 and (d) have a large band gap (>3 eV).…”

Section: Introductionmentioning

confidence: 99%

MoO _x /Ag/MoO _x multilayers as hole transport transparent conductive electrodes for n‐type crystalline silicon solar cells

et al. 2020

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Summary Substitution of highly doped layers with conventional transparent conductive electrodes as carrier collecting and selective contacts in conventional crystalline silicon (c‐Si) solar cell configurations is crucial in increasing affordability of solar cells by lowering material costs. In this study, oxide/metal/oxide (OMO) multilayers featuring molybdenum oxide (MoOx) and silver (Ag) thin films are developed by thermal evaporation technique, as dopant‐free hole transport transparent conductive electrodes (HTTCEs) for n‐type c‐Si solar cells. Semidopant‐free asymmetric heterocontact (semi‐DASH) solar cells on n‐type c‐Si utilizing OMO multilayers are fabricated. The effect of outer MoOx layer thickness and Ag deposition rate on the photovoltaic characteristics of the fabricated semi‐DASH solar cells are investigated. A comparison of front side pyramid textured and flat surface solar cells is performed to optimize the optical and electrical properties. Highest efficiency of 9.3% ± 0.2% is achieved in a pyramid textured semi‐DASH c‐Si solar cell with 15/10/30 nm of HTTCE structure.

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“…Passivated contact and carrier‐selective c‐Si solar cells show several intrinsic advantages in comparison with the heavily‐doped back‐surface‐field (BSF) solar cells, such as avoiding the severe recombination at the silicon‐metal contact and the Auger recombination in the heavily‐doped BSF region . Thus, passivated contact and carrier‐selective solar cells display improved surface passivation and carrier collection, leading to an enhanced open circuit voltage ( V oc ) and fill factor ( FF ).…”

Section: Introductionmentioning

confidence: 99%

“…In a previous publication, Mg with a work function of about 3.7 eV was used as the electron‐selective layer with a 6‐nm a‐Si:H passivation layer . Normally, the passivation layer usually employs two candidate materials: a high‐quality ultra‐thin (<2 nm) tunnel silicon oxide (SiO x ) film or a thin (∼5 nm) intrinsic a‐Si:H thin film . Comparing with the a‐Si:H thin passivation layer, the manufacture of SiO x layer does not require an expensive plasma‐enhanced chemical vapor deposition (PECVD) system and time‐consuming deposition process, which helps to lower the manufacturing cost.…”

Section: Introductionmentioning

confidence: 99%

Tunnel Oxide – Magnesium as Electron‐Selective Passivated Contact for n‐type Silicon Solar Cell

et al. 2018

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A tunnel silicon oxide (SiOx) and magnesium (Mg) electron‐selective structure and its application for n‐type c‐Si solar cell are carefully studied in this work. The fabrication, reflectance, passivation quality, contact resistivity, and thermal stability of the SiOx/Mg contact are investigated. The optimized thermally annealed SiOx at 700 °C leads to the best surface passivation and acceptable contact resistivity for the SiOx/Mg contact on an n‐type c‐Si wafer, i.e., the lowest single‐side surface saturated dark current (J0) of about 100 fA cm−2 and the contact resistivity of less than 30 mΩ cm−2 are achieved. In general, the SiOx/Mg structure exhibits robust performances to be used as an electron‐selective passivated contact for n‐type c‐Si solar cells.

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Stable Dopant-Free Asymmetric Heterocontact Silicon Solar Cells with Efficiencies above 20%

Cited by 177 publications

References 35 publications

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

MoO _x /Ag/MoO _x multilayers as hole transport transparent conductive electrodes for n‐type crystalline silicon solar cells

Tunnel Oxide – Magnesium as Electron‐Selective Passivated Contact for n‐type Silicon Solar Cell

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Stable Dopant-Free Asymmetric Heterocontact Silicon Solar Cells with Efficiencies above 20%

Cited by 177 publications

References 35 publications

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

MoO x /Ag/MoO x multilayers as hole transport transparent conductive electrodes for n‐type crystalline silicon solar cells

Tunnel Oxide – Magnesium as Electron‐Selective Passivated Contact for n‐type Silicon Solar Cell

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MoO _x /Ag/MoO _x multilayers as hole transport transparent conductive electrodes for n‐type crystalline silicon solar cells