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In this paper, we evaluate p-type passivated emitter and rear locally diffused (p-PERL) and n-type passivated emitter and rear totally diffused (n-PERT) large area silicon solar cells featuring nickel/copper/silver (Ni/Cu/Ag) plated front side contacts. By using front emitter p-PERL and rear emitter n-PERT, both cell structures can be produced with only a few adaptations in the entire process sequence because both feature the same front side design: homogeneous n+ diffused region with low surface concentration, SiO2/SiNx:H passivation, Ni/Cu/Ag plated contacts. Energy conversion efficiencies up to 20.5% (externally confirmed at FhG-ISE Callab) are presented for both cell structures on large area cells together with power-loss analysis and potential efficiency improvements based on PC1D simulations. We demonstrate that the use of a rear emitter n-PERT cell design with Ni/Cu/Ag plated front side contacts enables to reach open-circuit voltage values up to 676 mV on 1–2 Ω cm n-type CZ Si. We show that rear emitter n-PERT cells present the potential for energy conversion efficiencies above 21.5% together with a strong tolerance to wafer thickness and bulk resistivity. Copyright © 2014 John Wiley & Sons, Ltd.

Thin film epitaxial silicon solar cells are considered a near future alternative to bulk silicon solar cells. However due to the limited thickness of the active layer they require efficient light trapping. Therefore we propose the development and implementation of such light confinement by means of a porous silicon (PS) intermediate reflector at the epi/substrate interface. The formation of the reflector is done by electrochemical etching of a highly doped Si substrate into a multilayer stack (Bragg-optical reflector), and is followed by epitaxial deposition of the active layer. The implementation of the PS reflector however requires detailed analysis of many problematic issues, foremost the optical optimisation of the stack for internal reflection at the Si/PS/Si interface. Other topics include the pore rearrangement during high-temperature CVD as well as the quality of the epitaxial layer grown on porous silicon. Another challenge is the resistance within the PS layers. For that purpose, SRP (Spreading Resistance Probe) and resistance measurements were performed to determine the conductive properties of rearranged PS. First cells with a 9-layer porous silicon reflector gave a very promising efficiency of 13.5% which is 1.5% higher compared to cells without internal reflector.

We propose a novel approach to thin-film silicon solar cells, namely the freestanding monocrystalline silicon layer transfer process with heterojunction emitter (FMS-HJ). High crystallographic quality mono-Si films were deposited on freestanding porous silicon (PS) films by chemical vapor deposition (CVD). These free-standing mono-Si (FMS) films were processed into solar cells by creating a-a-Si/c-Si heterojunction. In our preliminary experiments a thin-film FMS-HJ solar cell with 9.6% efficiency was realized in a 20-μμm-thin active layer. Copyright © 2005 John Wiley & Sons, Ltd.

The new idea to fire the screenprinted contacts through porous silicon antireflection coating is tested for the first time from the viewpoint of PS eligibility towards a rapid high-temperature process. The morphological analysis (TEM and SE) reveals that the thickness of PS after firing is slightly increased simultaneously with increasing of its porosity. As a result no significant changes in reflectance characteristics are observed. The firing of the contacts through PS does not destroy antireflection properties and can be successfully used as an alternative way for preparation of PS ARC for silicon solar cells.

Irradiation damage in n + -Si/p + -Si 1-x Ge x epitaxial diodes and n + -Si/p + -Si 1 -Ge x /n-Si epitaxial heterojunction bipolar transistors (HBTs) is studied as a function of germanium content, radiation source, and fluence. The degradation of electrical performance of the devices by irradiation increases with increasing fluence, while it decreases with increasing germanium content. The induced lattice defects in the Si 1-x Ge x epitaxial layer and Si substrate are studied by DLTS methods. In the Si 1-x Ge x epitaxial layer of diodes and HBTs, an electron capture level which is associated with interstitial boron is induced by irradiation, while electron capture levels corresponding to E center and divacancy are formed in the collector region for HBTs. The impact of the radiation source on the degradation of performance is correlated with simulations of the number of knock-on atoms and the nonionizing energy loss (NIEL).

The degradation of strained n+-Si/p+-Si1−xGex epitaxial diodes, which are irradiated at room temperature with 1 MeV electrons in a high-voltage transmission electron microscope, is investigated. Special attention is given to the influence of the germanium content on the degradation of electrical characteristics and on the introduction of lattice defects into the epitaxial layer. The diode degradation and the deep level density for the x = 0.12 diodes are larger than for the x = 0.16 diodes. This can be explained by the fact that germanium atoms act as recombination centres for vacancies and interstitials thus decreasing the generation rate of stable radiation defects and by the fact that the energy absorbed in the epitaxial layer during irradiation decreases with increasing germanium content due to the smaller stopping power of germanium atoms.