We report efficiencies of >24% being consistently achieved in mass-production of passivating-contact solar cells. Furthermore, the certified efficiency of cells from our pilot line has reached 25.3% with 730 mV open-circuit voltage. An analysis of the cell performance, including simulations, shows that the cells’ rear-side is nearly ideal, while there remains potential for further optimization of the front emitter and passivation.

Here we present the latest results of our double side contacted, all screen printed n-type mono silicon solar cell development. N-type Czochralski (n-Cz) silicon solar cell results are compared to those of standard p-type Cz (p-Cz) silicon and n-type epitaxial (np+ epi) wafers, produced by Crystal Solar, having an integrated epitaxial boron doped p+-silicon layer. The np+ epi and p-Cz wafers are processed applying the Hanwha Q CELLS Q.ANTUM technology process flow to make PERC cells in our production line including process adaptations to mono wafers while the n-Cz wafers are processed with an extended Q.ANTUM sequence including additional processing steps like cleaning steps and a BBr3 tube furnace diffusion to create the rear side boron p+-silicon layer. We achieve conversion efficiencies up to 21.8% for the n-type Cz silicon back junction solar cell with open circuit voltage values of 671mV. The p-type Cz silicon solar cell shows non-stabilized efficiencies up to 21.2%. The n-type epitaxial solar cells have efficiencies up to 21.7% with fill factor values of up to 82.1% due to the high rear side conductivity of the integrated epitaxial boron doped p+-silicon layer. The latter solar cell results demonstrate a new path to industrial solar cells with efficiencies >22% by combination of simple and robust solar cell processing and epitaxial wafer growth with built-in doping layers.

Reducing wafer thickness while increasing power conversion efficiency is the most effective way to reduce cost per Watt of a silicon photovoltaic module. Within the European project 20 percent efficiency on less than 100-mu m-thick, industrially feasible crystalline silicon solar cells ("20pl mu s"), we study the whole process chain for thin wafers, from wafering to module integration and life-cycle analysis. We investigate three different solar cell fabrication routes, categorized according to the temperature of the junction formation process and the wafer doping type: p-type silicon high temperature, n-type silicon high temperature and n-type silicon low temperature. For each route, an efficiency of 19.5% or greater is achieved on wafers less than 100 mu m thick, with a maximum efficiency of 21.1% on an 80-mu m-thick wafer. The n-type high temperature route is then transferred to a pilot production line, and a median solar cell efficiency of 20.0% is demonstrated on 100-mu m-thick wafers. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We investigate the wafer-thickness dependence of double-side contacted rear junction n-type solar cells, theoretically by PC1D simulations and experimentally. To get the correct input parameters for PC1D, we first fit PC1D simulation to a rear junction cell fabrication of a complete ingot. The simulated cell performance of thin cells is mainly influenced by short circuit current Jsc. For wafer-thickness < 100 μm, light trapping becomes challenging and causes a steep decline in Jsc. This Jsc loss can also be seen in an IQE drop at long wavelengths of fabricated thin cells. For wafer-thickness > 100 μm, only minor variation in efficiency is predicted by simulation, which makes the cell concept suitable for 100 to 200 μm thick wafers. Median cell efficiencies of 20% for 100 μm thin- 6” Cz Si cells are reported.

We study the dependence of solar cell parameters on base resistivity for double-side contacted n-type rear junction solar cells with boron emitter and local rear contacts. Experimental data for solar cells processed on n-type Cz Si wafers with base resistivities ranging from 2Ω·cm to 16Ω cm are compared to device simulations for the respective resistivity range. Our experimental data show the typical strong increase of efficiency with base resistivity in the range of 2 - 5Ω cm and at about 10Ω cm a saturation of efficiency with base resistivity sets in [1–4].Comparison of experimental and simulation results reveal that our experimental findings are closely reproduced assuming a constant bulk lifetime after solar cell processing. Furthermore the results of this study were implemented in an optimized solar cell process. With 14Ω cm n-type Cz as base material solar cell efficiencies of up to 20.9% on 243.4cm2 (total area) were achieved which was confirmed by Fraunhofer ISE CalLab.