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In this paper we analyze and model perovskite/c-Si tandem cells with front and rear polySi passivated contacts on the bottom cell. A high-efficiency tandem approach will benefit from the high V oc potential of a c-Si bottom cell with front and rear polySi passivated contacts while the combination with a high band gap, semi-transparent, perovskite top cell will largely diminish the UV-Vis parasitic absorption in a polySi front side layer on the c-Si cell. On the other hand since the J sc is strongly reduced in a tandem bottom cell, free carrier absorption, to which both front and rear polySi layers contribute, will become a relatively more important loss mechanism. We investigate the trade-off between the optical gains and resistive losses from reducing the polySi thickness for cell configurations without transparent conductive oxide (TCO) and also consider the potential of the combination with TCOs. From our optical simulations we conclude that optical losses in the polySi layers of 100 nm and below are limited when applied on the bottom cell. Taking into account resistive losses in the polySi layers of varying thickness the optimal thickness is found to be 50 nm. In combination with the high V oc values resulting from the application of polySi passivating contacts this offers a promising route to establish a bottom cell with high efficiency. The combination of very thin polySi with highly transparent TCOs is likely to further improve bottom cell performance. [ABSTRACT FROM AUTHOR]

We investigate contacting of n- and p-type polysilicon (polySi) passivating contact layers with industrial screen-printed metal pastes, examining both fire through (FT) and non-fire through (NFT) pastes. The n- and p-type polySi layers, deposited by low pressure chemical vapour deposition and doped by POCl 3 diffusion, phosphorus implant, or BBr 3 diffusion, result in excellent J o , even for 50 nm thickness (<2 fA/cm 2 for n-polySi, <10 fA/cm 2 for p-polySi). The contact recombination is investigated by photoluminescence, and by cell test structures to determine V oc as a function of metallization fraction. The contact resistance is investigated by transfer length method (TLM). The contacts are also extensively studied by high resolution electron microscopy. All-polySi solar cells (i.e., cells with front and back carrier selective layers consisting of polySi) are prepared. Excellent implied V oc values of nearly 730 mV and 710 mV are obtained on the un-metallized polished and textured cells, respectively. The contact recombination after applying screen printed metallization can be analyzed well with both methods (PL and V oc -based) rendering values for the prefactor of the recombination current J o,c at the contact areas of about 400 and 350 fA/cm 2 for 200 nm thick n-polySi and p-polySi, respectively. [ABSTRACT FROM AUTHOR]

The perovskite solar cell is considered a promising candidate as the top cell for high-efficiency tandem devices with crystalline silicon (c-Si) bottom cells, contributing to the cost reduction of photovoltaic energy. In this contribution, a simulation method, involving optical and electrical modelling, is established to calculate the performance of 4-terminal (4T) perovskite/c-Si tandem devices on a mini-module level. Optical and electrical characterization of perovskite and c-Si solar cells are carried out to verify the simulation parameters. With our method, the influence of transparent conductive oxide (TCO) layer thickness of perovskite top cells on the performance of tandem mini-modules is investigated in case of both tin-doped indium oxide (ITO) and hydrogen-doped indium oxide (IO:H). The investigation shows that optimization of TCO layer thickness and replacement of conventional ITO with highly transparent IO:H can lead to an absolute efficiency increase of about 1%. Finally, a practical assessment of the efficiency potential for the 4T perovskite/c-Si tandem mini-module is carried out, indicating that with a relatively simple 4T tandem module structure the efficiency of a single-junction c-Si mini-module (19.3%) can be improved by absolute 4.5%. [ABSTRACT FROM AUTHOR]

In this work, we investigate polysilicon passivation contacts, to be used for high performance IBC cells. We demonstrate an LPCVD process for in-situ p-type doped polysilicon. The p-type polysilicon can be locally overcompensated to n-type polysilicon using phosphorous implantation or POCl 3 diffusion. Both contacts show excellent surface passivation, with recombination current (J o ) of 12 fA/cm 2 for p-poly on a polished Si surface, and less than 10 fA/cm 2 for compensated n-poly both on textured and polished surfaces. These polysilicon layers are implemented in the fabrication of n-PERT cells with front and rear polysilicon contacts. The resulting textured half-fabricated cells have an implied V oc of 701 mV after hydrogenation via PECVD deposition of SiN x :H. Different metallization processes, relevant for IBC cells, are applied. A V oc of 685 mV is obtained for the best cell metallized with low-temperature metallization (ITO/low-temperature Ag paste), and 678 mV is obtained for the best cell with industrial screen-printed firing-through contacts. In these n-PERT cells the same thin oxide layer is used for p-type and n-type polysilicon contacts. [ABSTRACT FROM AUTHOR]

The back junction back contact cell, and more specifically the interdigitated back contact (IBC) cell is among the most appropriate cell designs to achieve highly efficient solar cells. An important aspect to improve manufacturability (e.g. reduce cost) of the cell and module is to increase the rear side back surface field (BSF) region width, as this currently constitutes the smallest feature size in the diffusion pattern of the IBC cell. We propose a novel design of an IBC cell that enhances the effective lateral transport of minority carriers (holes) and therefore allowing wide BSF regions. The novel design feature is to implement an appropriate conductive and well passivated p ++ -doped layer, referred to as a front floating emitter (FFE), on the front surface of the IBC cell. This conductive FFE enables equally-sized interdigitated doping patterns of positive and negative polarities on the rear, with similar cell pitch and efficiency compared to traditional IBC cells. It also enables larger interconnection pads for easier module interconnection with marginal loss of cell performance. Additional advantages are expected from relaxed alignment tolerances for patterning as well as interconnection. We report on the proof-of-principle of this new cell concept, which we name “Mercury”, brought forward by 2D simulations and experimental results on small and 6 inch cells, based on an industrial process flow with stable results. So far, these cells yield efficiencies up to 19.4% and short-circuit densities well above 41 mA/cm 2 . Additionally, the Mercury cells show less efficiency loss at low illumination intensity than a standard p-type H-pattern cell. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes results of metal wrap through (MWT) cells produced from n-type Czochralski silicon wafers, and modules produced from those cells. The use of n-type silicon as base material allows for high efficiencies: for front emitter contacted industrial cells, efficiencies upto nearly 20% have been reported. MWT cells allow even higher cell efficiency, and additionally full back-contacting of the MWT cells in a module results in reduced cell to module (CTM) losses. MWT cells were produced by industrial process technologies. The efficiency of the MWT cells reproducibly exceeds the front contact cells based on the same technology by about 0.2-0.3%, and routes for further improvement are analysed. 60-cell modules were produced from both types of cells. The MWT module, based on integrated backfoil, produced 3% higher power output than the comparable tabbed front emitter contact module. In particular differences in CTM loss of current and fill factor will be presented. CTM current differences arise from the higher packing density, and lower reflectance of the backfoil, in MWT modules. CTM FF differences are related to resistive losses in copper circuitry on the backfoil versus tabs. The CTM FF loss of the MWT module was 2.2%abs lower than for the tabbed front emitter contact module. Also here the losses are analysed and routes for improvement discussed. [Copyright &y& Elsevier]

Abstract: The use of n-type, instead of p-type, silicon wafers for the production of mc-Si solar cells has a clear effect on the pre-breakdown behavior under reverse bias conditions. In p-type solar cells, material related breakdown patterns that are commonly observed in luminescence and thermography images. These patterns do not appear in the investigated n-type mc-Si solar cells, at least not down to a reverse bias of -16V. To the best of our knowledge, this difference between p-type and n-type mc-Si solar cells has not yet been described in literature before and could provide important information for the understanding of this type of wafer related breakdown. [Copyright &y& Elsevier]

Abstract: Low “Euros per Watt-peak” and ease of industrialization are the main drivers towards successful introduction on the market. In this regard, back-contact solar cells on n-type silicon offer significant benefits. The efficiency of back contact cells, such as Metal Wrap Through (MWT) cells, compared to the traditional H-pattern cells is higher at cell level, thanks to the reduced shading losses, and is higher at module level, thanks to the reduced interconnection resistance losses. N-type silicon benefits from improved electrical properties of n-type silicon compared to p-type (higher minority carrier diffusion lengths, lower sensitivity to many impurities). Furthermore, the availability of an industrial cell process designed by ECN, resulting in bifacial cells (good rear surface passivation and light trapping), makes n-type silicon a perfect candidate for high efficiency solar cells and requires only modest changes to the current wafer and cell production processes. In order to reduce processing costs and increase module efficiencies, we have started two years ago the development of the Metal-Wrap-Through (MWT) solar cell technology on n-type mono-crystalline silicon wafers. Within the last year, efficiency of our MWT silicon solar cells manufactured from ntype Cz silicon wafers has been improved by 1% absolute. Based on common industrial cell processing steps such as diffusion, screen-printing metallization and firing through, we have obtained efficiencies up to 19.70% (in-house measurements) on large area wafers (239cm2, 5Ωcm), with clear potential for further improvement. In this article, we present a first direct comparison experiment between n-type bifacial MWT and “conventional” n-type bifacial Hpattern technologies, in which an efficiency gain of 0.30% absolute for MWT is demonstrated. At the moment, series resistance and, as a result, fill factor are still sub-optimal. Nevertheless, with current density (Jsc) values approaching 40mA/cm2 and open circuit voltage of 644mV, n-type MWT solar cells already outperform n-type H-pattern cells manufactured with a comparable process. [Copyright &y& Elsevier]

Abstract: A record efficiency of 16.4% (156.25cm2) has been achieved for an n-type wafer-based (hereafter, “n-based”) mc-Si solar cell. A horizontal quartz tube furnace with an industry-compatible scale is employed for forming a p+-emitter using boron tribromide (BBr3) as the boron source, in which system less contamination is confirmed than in other options of boron diffusion. A significantly homogeneous emitter is achieved with the standard deviation of 1.5Ω/sq. n-Based mc-Si solar cells are fabricated with phosphorus-diffused BSF, SiN deposition, and fire-through screen-printed contacts. The properties of the best cell are; η: 16.4%, V oc: 607mV, J sc: 35.2mA/cm2, and FF: 76.7%. [Copyright &y& Elsevier]

Abstract The perovskite/c-Si tandem technology is considered as a cost-effective approach to realize a cell efficiency beyond the limit of single-junction (SJ) c-Si cells. Compared to its counterpart of 2-terminal (2T) configuration, 4-terminal (4T) tandem has the advantages such as no constraint of current matching and potentially simple mechanical stacking. But one of the largest challenges is the limited near-infrared (NIR) transmission of the semi-transparent perovskite solar cell (ST-PSC), which has been a bottleneck to the c-Si bottom cell performance and eventually the whole tandem cell performance. The highest NIR transmittance that has been reported is about 84%. In this contribution, we demonstrate a p-i-n planar ST-PSC with an efficiency as high as 15.7% and with a record NIR transmittance of about 92%. It is realized by optimization of the tin-doped indium oxide (ITO) material properties and light management. This NIR-transparent and high-efficiency ST-PSC leads to a 4T tandem cell efficiency of 25.7%, using an interdigitated-back-contact (IBC) c-Si bottom cell. Highlights • Record near-infrared transmittance of 92% for semi-transparent perovskite solar cells. • Detailed optical loss analysis carried out with validated optical models and input parameters. • 4-terminal perovskite/c-Si cell efficiency of 25.7%. [ABSTRACT FROM AUTHOR]

We present a high-performance bifacial n-type solar cell with LPCVD n + polysilicon (polySi) back side passivating contacts and fire-through screen-printed metallization, processed on full area 6″ Cz wafers. The cells were manufactured with low-cost industrial process steps yielding a best efficiency of 20.7%, and an average V oc of 674 mV. We analysed effects of variation of doping level, thickness, and oxide properties of the n-type polySi/SiO x layers, as well as hydrogenation from a PECVD SiN x :H coating, which led to recombination current densities down to ~2 fA/cm 2 and ~4 fA/cm 2 on planar and textured surface, respectively. Analysis shows that the wafer bulk lifetime in the cell is high and that the V oc of the cell is limited by the J o of the uniform diffused boron emitter and its contacts. Ways to improve the efficiency of the cell to >22% are indicated. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows how the amorphous/crystalline silicon technology can be implemented in the interdigitated back contact solar cell design. We have fabricated rear-junction, backside contact cells in which both the emitter and the back contact are formed by amorphous/crystalline silicon heterostructure, and the grid-less textured front surface is passivated by a double layer of amorphous silicon and silicon nitride, which also provides an anti-reflection coating. The entire self-aligned mask and photolithography-free process is performed at temperature below 300°C with the aid of one metallic mask to create the interdigitated pattern. An open circuit voltage of 687mV has been measured on a 0.5Ωcm p-type monocrystalline silicon wafer. On the other hand, several technological aspects that limit the fill factor (50%) and the short circuit current density (32mA/cm2) still need improvement. We show that the uniformity of the deposited amorphous silicon layers is not influenced by the mask-assisted deposition process and that the alignment is feasible. Moreover, this paper investigates the photocurrent limiting factors by one-dimensional modeling and quantum efficiency measurements. [Copyright &y& Elsevier]