Search

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]

Monolithic perovskite/silicon tandem photovoltaics have fueled major research efforts as well as gaining rapid industrial interest. So far, most of the literature has focused on the use of currently more expensive silicon heterojunction bottom cell technology. This work demonstrates a perovskite/silicon tandem solar cell based on the industrially dominant passivated emitter and rear cell (PERC) technology. In detail, we investigate a tunnel recombination junction (TRJ) consisting of ITO/NiO/2-(9 H -carbazol-9-yl)ethyl] phosphonic acid (2PACz) and compare it with an ITO/2PACz TRJ. Specifically, the NiO layer is deposited by atomic layer deposition (ALD). Although ITO/2PACz-based tandem devices can reach more than 24% conversion efficiency, we observe that they suffer from a large spread in photovoltaic parameters due to electrical shunts in the perovskite top cell, caused by the inhomogeneity of the 2PACz layer on ITO. Instead, when ALD NiO is sandwiched between 2PACz and ITO, the surface coverage of 2PACz improves and the yield of the devices, in terms of all device parameters, also improves, i.e. , the standard deviation decreases from 4.6% with ITO/2PACz to 2.0% with ITO/NiO/2PACz. In conclusion, thanks to the presence of NiO, the TRJ consisting of ITO/NiO/2PACz leads to a 23.7% efficient tandem device with narrow device efficiency distribution. • Champion 23.7% efficient perovskite-PERC tandem cell was achieved. • The developed thermal atomic layer deposition (ALD) process for NiO is reported. • ALD NiO was added to an ITO/SAM recombination junction to improve the device yield. [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]