We apply stacks of silicon nitride (SiNX) layers consisting of phosphorus-doped SiNX (SiNX: P) and undoped SiNX as first and second layer, on the front surface of p-type monocrystalline silicon passivated emitter and rear cells (PERC). The stack is deposited using plasma-enhanced chemical vapor deposition. These layer stacks provide excellent surface passivation and anti-reflection properties comparable to single undoped SiNX layers. A laser processing locally introduces the phosphorus dopants from the SiNX: P/SiNX layer stack into the silicon and locally removes the layer stack. Thereby, local highly doped areas with sheet resistances as low as R-sh approximate to 20 Omega/sq are obtained. We refer to this as the nPassDop approach, which provides local high doping and structuring of the anti-reflection coating in one process. The saturation current density of the laser processed areas is estimated to be as low as j(0, laser) approximate to 500 fA/cm (2). First implementations for large-area p-type Cz-Si PERC cells with self-aligned NiCuAg plated front contacts yield an energy conversion efficiency of 19.6%.

The authors discuss industry related approaches at Fraunhofer ISE for bifacial p-type silicon solar cells, taking into account the well-known “passivated emitter and rear cell” (PERC), “passivated emitter and rear totally diffused” (PERT) and “passivated emitter and locally diffused” (PERL) architectures. In the case of PERC, challenges in terms of alignment, printability and the importance of bifaciality are addressed. In the case of PERT, a co-diffusion process is utilized to form the emitter and the back surface field simultaneously avoiding also critical shunts that can arise at the edges of such devices. For the PERL technology, the industrial feasible pPassDop approach is discussed. We report on front side energy conversion efficiencies for PERC of 21.4%, PERT of 20.5%, and PERL of 19.8%. Furthermore, bifaciality factors for PERC of 0.7, for PERT of 0.86, and for PERL of 0.89 are presented.

To investigate the rear side of bifacial p-type Czochraslki-grown silicon PERC solar cells, the present work combines Sentaurus Device simulation – calibrated with extensively characterized samples – and the subsequent fabrication of solar cells according to the simulation findings. The authors investigate the physical alteration of rear-side characteristics in the context of an additional rear-side illumination. The additional injection represents an further factor for the balance of carrier generation, recombination and series resistances which in turn influences the design rules for the rear side layout. Our detailed bifacial simulations include these physical aspects and we derive design solutions for different bifacial illumination scenarios for a bifacial p-doped PERC solar cell. Using an industrial PERC process, solar cells with laser contact openings (LCO) and a rear aluminum grid were produced according to the simulation results with a wide variation in rear side layout parameters. The PERC batches showed a rather constant medium (front side) efficiency of η = 20.8±0.2% and a bifaciality of 66 to 77% depending on the rear layout, allowing us to investigate the rear-side characteristics in detail and to compare them with the effects predicted by the simulations. We processed an aluminum rear contact grid with finger widths as small as 100 µm and successfully aligned it onto the LCO with 30 µm contact openings on full-area 156x156 mm2 wafers. We reached good accordance between the monofacial measurements from front and rear side and our simulation model and could thus predict bifacial illumination results by modeling for two issues: 1. Planar rear sides have an advantage over pyramid textured rear sides for 1000 W/m² front illumination unless additional rear illumination exceeds 250 W/m². 2. As soon as any rear illumination is added to the front-illuminated PERC solar cell, 100 µm thin fingers at the rear side have an output power advantage compared to 150 µm and 200 µm wide fingers.

This work aims to improve the rear-side properties of p-type monocrystalline silicon solar cells by using the passivated emitter and rear locally diffused (PERL) solar cell concept. To realize the rear side structure, the so-called PassDop approach was used combining both surface passivation and local doping. The concept utilizes a multifunctional, doped AlOx/SiNx:B layer stack; the localized structuring is achieved by local contact opening and doping by a laser process. Using AlOx/SiNx:B PassDop layers, an outstanding effective surface recombination velocity S-eff of less than 4 cm/s was achieved after firing at the passivated area. The boron concentration in the PassDop layers did not show any significant influence on S-eff. Laser doping resulted in highly doped regions in the silicon with a sheet resistance of below 20 Omega/sq and surface doping concentrations close to 1 x 10(20) cm(-3). Accordingly, calculations showed that the saturation current density at the laser doped areas can be as low as 900 fA/cm(2) for line-shaped contact structures.

We present 6-inch bifacial p-type Czochralski-grown silicon passivated emitter and rear locally-diffused (PERL) solar cells with “pPassDop” layer stack on the cell’s rear side. The “pPassDop” layer stack consists of an aluminum oxide and a boron-doped silicon nitride layer serving as both surface passivation and doping source. Local laser processing introduces boron and aluminum atoms from the “pPassDop” layer stack into the silicon. The electrical contacting of the formed line-shaped p-doped back surface field is realized by screen-printed and fired pure silver contacts (i.e. without aluminum). The fabricated PERL solar cells reach high bifaciality of up to 89%. The monofacial peak front side energy conversion efficiency, measured with contact bars on both sides on a black non-conducting chuck, is given by 19.8%. Fill factors of more than 79% and specific contact resistances in the single-digit mΩcm2range prove the successful low-resistance contacting on both sides. It is important to stress that the same commercial state-of-the-art firing-through pure silver screen-printing paste is used for the cell’s front and rear side metallization. A special alignment procedure ensures that the rear silver grid with finger widths of about 65 μm is placed over the whole wafer on top of the about 37 μm-wide laser-doped and opened structures.

The PCVD (Photo Current/Voltage Decay)-method supplies a possibiliy to determine the effective backside recombination velocity SB and the emitter saturation current I0E if the bulk diffusion length Ln of the solar cell is known. An evaluation method is described which allows under inclusion of a spectral response measurement the determination of all three parameters Ln, SB and I0E. The applicability of the method to characterize screenprinted silicon solar cells is demonstrated. The emitter saturation current of different POCl3-diffused and screenprinted emitters is measured and compared with calculated values using the programm PC1D. The bulk-passivation due to a fired silicon nitride is shown. Even on mechanically V-textured screenprinted solar cells the emitter saturation current is mesured. Finally, with CV-measurements the influence of the deposition parameters on the interface properties of LF-PECVD silicon nitride layers is measured.

The state‐of‐the‐art low‐ohmic electrical contacting of highly boron‐doped silicon surfaces is based on the use of screen‐printed and fired silver‐aluminum (Ag‐Al) contacts. For these contacts, metal crystallites with depths of up to a few microns are observed at the interface. For screen‐printed and fired Ag contacts on phosphorus‐doped surfaces, the observed crystallite depths are much smaller. In this work, low‐ohmic electrical contacting of local laser‐doped p‐type silicon surfaces with commercial pure Ag screen‐printing paste are demonstrated. The doping layer is based on the “pPassDop” approach, which serves as a passivation layer on the rear side of p‐type silicon solar cells. The specific contact resistances are measured down to 1 mΩ cm2 for p‐type doping densities of about 3 × 1019 cm−3 at the silicon surface and finger widths of around 55 μm. Microstructure analysis reveals the formation of numerous small Ag crystallites at the interface with penetration depths of less than 80 nm. A first implementation of the “pPassDop” approach on 6‐inch p‐type Cz‐Si bifacial solar cells using solely Ag contacts on both sides results in a peak front side energy conversion efficiency of 19.1%, measured on a black chuck with contact bars on both sides.

We present the development of aluminum oxide (AlOx) and boron-doped silicon nitride (SiNx:B) layer stacks for application on the back side of monocrystalline p-type silicon wafers. Two deposition techniques are used for the deposition of the AlOx/SiNx:B layer stacks, atomic layer deposition and plasma-enhanced chemical vapor deposition. Both techniques enable excellent surface passivation with surface recombination velocities of 4 cm/s after firing. Also, heavy local doping with sheet resistances down to 20 Ω/sq is possible by laser processing. We call this concept the PassDop approach. For the laser processed area where the silicon surface is locally boron-doped and the AlOx/SiNx:B passivation layer stack is locally removed, a quite low dark saturation current density of about 900 fA/cm2 is determined. The PassDop approach can be a solution to realize passivated emitter and rear locally doped PERL solar cells by improving their rear side properties while maintaining industrial applicability.

As electromagnetic absorption materials with broadband absorption are highly pursued in the recent development of cutting‐edge electronic and telecommunication industries, the traditional uniform bulk composites with dielectric and magnetic active absorbers are attracting extensive interest, with remaining concerns of extending the effective absorption bandwidth. To understand the impact of using dielectric‐magnetic coupled absorption fillers and to implement artificial absorption structures in the absorption performance, in this work, both nanoscale nonmagnetic and magnetic graphene hybrid fillers are prepared as the effective absorbers. In the comparison based on the microscopic studies, magnetic graphene fillers are found to possess dual absorption bands in the investigation region, which is responsible for extending the effective absorption bandwidth. With subsequent macroscopic structure design based on the as‐fabricated composites, the artificial structures established on the composites embedded with magnetic graphene fillers exhibit more broadened absorption bandwidth because of the exclusive advantages of absorption from multiple thickness and greater interfacial impedance matching. The results suggest that combination of developing microscopic dielectric‐magnetic coupled absorbers and macroscopic structure design will fundamentally extend the effective absorption bandwidth of the electromagnetic absorption materials.

The efficiency record of industrial type PERC solar cells exceeded 22% at the turn of the year 2015 to 2016. Our best screen-printed PERC solar cell reached 22.04% efficiency while the best cell batch showed a very narrow efficiency distribution. A detailed electrical and optical loss analysis of those industrial type high efficiency PERC solar cells is carried out which enables further optimization and strategic improvements. A variety of characterization data allows for a recombination current density, resistance and optical loss analysis based on numerical device simulation, analytical calculations and raytracing, respectively. The main recombination losses at maximum power point (MPP) occur in the homogenous and selective diffused regions of the emitter. A series resistance loss analysis is analytically performed. The emitter contribution to the lumped series resistance dominates the series resistance losses. The optical loss analysis performed with raytracing shows main reflection and absorption losses in the rear metal layer which is partly due to the light trapping capability of the PERC cells.

Thermophotovoltaics (TPV) was intensively investigated as a technology for heat/electricity co-generation in the last decade of the 20th century. However, a wide-spread commercialisation has not been achieved yet. The world-record system efficiency for a TPV system using silicon photocells of 4% at 50W electrical output power as well as a maximum electrical output power of 164W, however at a lower efficiency of 0.84% could be demonstrated by a prototype system operating with an Yb2O3 selective emitter. Related developments of TPV system components such as radiation emitters, filters and photocells are reviewed and theoretical system simulations are compared to experimentally achieved results regarding system efficiency and the electrical output power. Finally, novel TPV applications are suggested and the commercial potential of this technology is discussed.

Most high-efficiency concepts for silicon solar cells utilise passivated surfaces and/or novel metallisation approaches. For these devices an anneal step, preferential in forming gas ambient, is beneficial or even crucial. Annealing is known to activate or improve surface passivation, facilitate metal-silicide formation, improve adhesion of metal contacts and cure potential crystal damage. Challenges for industrial solutions of anneal processes are a precise control of the process atmosphere and temperature, as well as a high throughput and easy integration into production lines. We present a high capacity inline annealing system that addresses these tasks with a throughput of over 1000 wafers per hour. The gas locks, located at the entrance and exit of the furnace, allow for an effective separation of laboratory and forming gas process ambient, which results in a residual oxygen concentration of a few ppm. Inline annealed silicon solar cells with a thermal oxide passivated rear surface show the same conversion efficiency as reference cells, which are annealed in a single wafer reactor. The specific cost of inline annealing in forming gas is calculated to be below 1.1 €ct/Wp.