Silicon solar cells on glass with power conversion efficiency above 13 at thickness below 15 micrometer

Liquid phase crystallized silicon on glass with a thickness of 10 40 amp; 956;m 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 cm 2 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 amp; 956;m 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 10 17 cm 3 and 2 10 16 cm 3 . 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 cm 2 test structure circumvents limitations of the contact design reaching an efficiency of 15.9 clearly showing the potential of the technolog

Influence of doping concentration and contact geometry on the performance of interdigitated back contact silicon heterojunction of liquid phase crystalline silicon on glass

This work reports on the effect of doping concentration and contact geometry in interdigitated back contact silicon heterojunction IBC SHJ cell with liquid phase crystallized silicon LPC Si . Doping concentration of 3 10 16 cm 3 and back surface field BSF finger width of 120 amp; 956;m at emitter width of 1080 amp; 956;m are demonstrated as optimized conditions to get the highest average cell efficiency. Spatially resolved methods such as light beam induced current LBIC , photoluminescence PL and electroluminescence EL were used to investigate current losses. LBIC records showed that back surface field BSF fingers were not well passivated and caused a loss of 2.6 2.7 mA cm 2 . Grain boundaries GBs dislocations mainly contributed to a current loss of 3.6 4.0 mA cm 2 corresponding to a relative loss of 11 1

Analysis of Local Minority Carrier Diffusion Lengths in Liquid Phase Crystallized Silicon Thin Film Solar Cells

We develop a method to quantify the local minority carrier diffusion lengths in interdigitated back contact solar cells having a 10 m thick liquid phase crystallized LPC Si absorber by light beam induced current LBIC measurements. The method is verified by 2 D simulations of the LBIC signals using ASPIN3. The effective minority carrier diffusion lengths determined this way range between 33 and 44 m inside a grain, which proves that advanced cell concepts like an interdigitated back contact IBC system are well suited for the LPC absorbers. Furthermore, the method has the potential to help improve the optimization of contact system geometries, and it may be used to understand the influences of different grain orientations and improve the LPC Si absorber fabrication proces

Assessment of Bulk and Interface Quality for Liquid Phase Crystallized Silicon on Glass

This paper 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 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 amp; 956;s for n type LPC Si with a doping concentration in the order of 10 16 cm amp; 8722;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 amp; 956;m and show a diffusion length of 0.4 amp; 956;m. 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 two dimensional 2 D 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 V oc , indicating back surface passivation problem. The results showed that V oc losses are not only because of poor back surface passivation but also because of crystal defects such as GBs and dislocatio