Sven Kühnapfel

Silicon Thin-Film Solar Cells on Glass With Open-Circuit Voltages Above 620 mV Formed by Liquid-Phase Crystallization

Liquid-phase crystallization (LPC) using line-shaped energy sources such as laser or electron beam has proven to be a suitable method to grow large grained high-quality silicon films onto commercially well-available glass substrates. In this study, we compare cw-diode laser-crystallized absorbers with electron beam-crystallized material using back contacted back junction solar cells. Furthermore, the influence of the absorber doping concentration thickness on the solar cell performance is studied. Using experimental data obtained on test structures, as well as solar cells and 1-D device simulations, an ideal dopant concentration is determinedtobe 2 - 6 × 1016cm-3, in combination with an absorber thickness of 10-20 μm. Finally, we present a slightly modified cell process to reduce the optical losses, which resulted in conversion efficiencies of up to 11.8%.

Influence of Barrier and Doping Type on the Open-Circuit Voltage of Liquid Phase-Crystallized Silicon Thin-Film Solar Cells on Glass

We investigate the influence of the barrier type and the absorber doping on the open-circuit voltage of liquid phase-crystallized silicon solar cells on glass. It was found that the use of n-type instead of p-type substrates is the major reason for the recently reported boost of the open-circuit voltage (VOC) up to values of 656 mV, which is by far exceeding the previously reported VOC values of crystalline silicon solar cells on glass. Despite the high doping, locally, an internal quantum efficiency of 90% can be achieved. Therewith, efficiencies of 16% and up should be possible.

Liquid-Phase Crystallized Silicon Solar Cells on Glass: Increasing the Open-Circuit Voltage by Optimized Interlayers for n- and p-Type Absorbers

Liquid-phase crystallization (LPC) has proven to be a suitable method to grow large-grained silicon films on commercially well-available glass substrates. Zone-melting crystallization with high-energy-density line sources such as lasers or electron beams enabled polycrystalline grain growth with wafer equivalent morphology. However, the electronic quality is strongly affected by the material used as the interlayer between the glass and the silicon absorber. Open-circuit voltages above 630 mV, and efficiencies up to 11.8% were demonstrated using n-type absorbers on a sputtered interlayer comprising a triple stack of SiO2/SiNx/SiO2. In this study, we present our results to further improve the device performance by investigating the influence of the interlayer on the open-circuit voltage of the devices and characterize the properties of the absorber and interface using bias light-dependent quantum efficiency data and transmission electron microscopy (TEM) images. Finally, we investigate the applicability of aluminum oxide (Al2O3) for passivation of p-type LPC absorbers.

Lifetime analysis of laser crystallized silicon films on glass

Only recently, the quality of liquid phase crystallized silicon directly on glass substrates made a huge leap towards the quality of multi-crystalline wafers with open circuit voltages well above 600 mV. In this paper, we investigate the material quality in order to identify the factors limiting further performance improvements. We employ photoluminescence imaging on a state of the art test structure with lifetime calibration by transient photoluminescence. The resulting lifetime map is converted into an effective diffusion length map and the origin of regions with short lifetimes is investigated with electron backscattering and transmission electron microscopy. High local dislocation densities in areas with dissociated coincidence site lattice boundaries were found to be responsible for the localised quenching of the photoluminescence signal.

Liquid phase crystallized silicon solar cells on glass: Material quality and device design

Liquid phase crystallization (LPC) has proven to be a suitable method to grow large-grained silicon films on commercially well available glass substrates. Zone-melting crystallization with high energy density line sources such as lasers or electron beams enabled polycrystalline grain growth with wafer equivalent morphology. A lot of effort was put into interlayer optimization by different groups. Open circuit voltages above 630 mV and efficiencies up to 11.8% were demonstrated using n-type absorbers on a sputtered interlayer between glass substrate and silicon absorber comprising a triple stack of SiO2/SiNx/SiO2. In this work we report on our results to further improve device performance by investigating the influence of the interlayer on the open circuit voltage of the devices and demonstrate first results achieved on an interdigitated back contacted silicon heterojunction solar cell to simplify device fabrication.