Liquid phase crystallized silicon on glass with a thickness of (10–40) μm has the potential to reduce material costs and the environmental impact of crystalline silicon solar cells. Recently, wafer quality open circuit voltages of over 650 mV and remarkable photocurrent densities of over 30 mA/cm2 have been demonstrated on this material, however, a low fill factor was limiting the performance. In this work we present our latest cell progress on 13 μm thin poly-crystalline silicon fabricated by the liquid phase crystallization directly on glass. The contact system uses passivated back-side silicon hetero-junctions, back-side KOH texture for light-trapping and interdigitated ITO/Ag contacts. The fill factors are up to 74% and efficiencies are 13.2% under AM1.5 g for two different doping densities of 1 · 1017/cm3 and 2 · 1016/cm3. The former is limited by bulk and interface recombination, leading to a reduced saturation current density, the latter by series resistance causing a lower fill factor. Both are additionally limited by electrical shading and losses at grain boundaries and dislocations. A small 1 × 0.1 cm2 test structure circumvents limitations of the contact design reaching an efficiency of 15.9% clearly showing the potential of the technology.

Liquid phase crystallization of silicon (LPC-Si) on glass is a promising method to produce high quality multi-crystalline Si films with macroscopic grains. In this study, we report on recent improvements of our interdigitated back-contact silicon heterojunction contact system (IBC-SHJ), which enabled open circuit voltages as high as 661 mV and efficiencies up to 14.2% using a 13 µm thin n-type LPC-Si absorbers on glass. The influence of the BSF width on the cell performance is investigated both experimentally and numerically. We combine 1D optical simulations using GenPro4 and 2D electrical simulations using Sentaurus™ TCAD to determine the optical and electrical loss mechanisms in order to estimate the potential of our current LPC-Si absorbers. The simulations reveal an effective minority carrier diffusion length of 26 µm and further demonstrate that a doping concentration of 4×10 16 cm-3 and a back surface field width of 60 µm are optimum values to further increase cell efficiencies.

Liquid‐phase crystallization (LPC) of silicon is a suitable method to grow large grained poly‐crystalline silicon with wafer equivalent electronic quality on cheap glass substrates. Dielectric layers between glass and silicon (called interlayer) are not only crucial for the solar cell performance, but, they also provide wetting of the silicon during crystallization. So far, LPC‐Si samples based on interlayers grown with plasma‐enhanced chemical vapor deposition (PECVD) were annealed prior to crystallization to remove hydrogen in order to prevent delamination during crystallization. However, this step increases manufacturing time and disables integrated processing without extended vacuum breaks. In this work, PECVD‐grown stacks with silicon oxide and silicon nitride, that is, SiOx/SiNx/SiOx (O/N/O), were developed aiming a high cell performance and a successful crystallization without prior annealing step. We found that the SiNx layer significantly influences adhesion and that an O/N/O stack with a nitrogen‐rich SiNx layer in which hydrogen is only bonded to nitrogen, that is, no Si–H bonds, provides wetting without annealing step. The total amount of bonded hydrogen in the SiNx film was not crucial. Finally, based on the presented O/N/O stack, LPC‐Si solar cells with almost 630 mV open circuit voltage and a conversion efficiency of up to 13.2% were obtained.

This work reports on the electrical quality of liquid phase crystallized silicon (LPC-Si) on glass for thin-film solar cell applications. Spatially resolved methods such as light beam induced current (LBIC), microwave photoconductance decay (MWPCD) mapping and electron backscatter diffraction (EBSD) were used to access the overall material quality, intra-grain quality, surface passivation and grain boundary (GB) properties. LBIC line scans across GBs were fitted with a model to characterize the recombination behavior of GBs. According to MWPCD measurement, intra-grain bulk carrier lifetimes were estimated to be larger than 4.5 µs for n-type LPC-Si with a doping concentration in the order of 10 16 cm -3 . Low-angle GBs were found to be strongly recombination active and identified as highly defect-rich regions which spatially extend over a range of 40-60 µm and show a diffusion length of 0.4 µm. Based on absorber quality characterization, the influence of intra-grain quality, heterojunction interface and GBs/dislocations on the cell performance were separately clarified based on 2D-device simulation and a diode model. High back surface recombination velocities of several 10 5 cm/s are needed to get the best match between simulated and measured open circuit voltage (Voc), indicating back surface passivation problem. The results showed that Voc losses are not only due to poor back surface passivation but also due to crystal defects such as GBs and dislocation.

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