Florent Sahli

Transparent Electrodes in Silicon Heterojunction Solar Cells: Influence on Contact Passivation

Charge carrier collection in silicon heterojunction solar cells occurs via intrinsic/doped hydrogenated amorphous silicon layer stacks deposited on the crystalline silicon wafer surfaces. Usually, both the electron and hole collecting stacks are externally capped by an n-type transparent conductive oxide, which is primarily needed for carrier extraction. Earlier, it has been demonstrated that the mere presence of such oxides can affect the carrier recombination in the crystalline silicon absorber. Here, we present a detailed investigation of the impact of this phenomenon on both the electron and hole collecting sides, including its consequences for the operating voltages of silicon heterojunction solar cells. Based on our findings, we define guiding principles for improved passivating contact design for high-efficiency silicon solar cells.

Fully textured monolithic perovskite/silicon tandem solar cells with 25.2% power conversion efficiency

Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve power conversion efficiencies above 30% at reasonable costs. State-of-the-art monolithic two-terminal perovskite/silicon tandem devices have so far featured silicon bottom cells that are polished on their front side to be compatible with the perovskite fabrication process. This concession leads to higher potential production costs, higher reflection losses and non-ideal light trapping. To tackle this issue, we developed a top cell deposition process that achieves the conformal growth of multiple compounds with controlled optoelectronic properties directly on the micrometre-sized pyramids of textured monocrystalline silicon. Tandem devices featuring a silicon heterojunction cell and a nanocrystalline silicon recombination junction demonstrate a certified steady-state efficiency of 25.2%. Our optical design yields a current density of 19.5 mA cm−2 thanks to the silicon pyramidal texture and suggests a path for the realization of 30% monolithic perovskite/silicon tandem devices.An optimized two-step deposition process allows the formation of uniform layers of metal halide perovskites on textured silicon layers, enabling tandem silicon/perovskite solar cells with improved optical design and efficiency.

Transparent electrodes in silicon heterojunction solar cells: Influence on carrier recombination

Hole and electron collectors in silicon heterojunction solar cells consist of hydrogenated amorphous silicon layer stacks deposited on the crystalline silicon wafer surfaces. Charge carrier extraction from these layers is achieved by electrodes consisting of a transparent conductive oxide and a metal layer. Earlier, the mere presence of the transparent conductive oxide layer on top of the hole collecting stack was shown to alter minority carrier lifetimes, at low minority injection levels, of the crystalline silicon absorber. In this work, we present a detailed investigation of the magnitude and nature of these effects and discuss their impact on silicon heterojunction solar cell performance for the different device architectures.