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

Low Temperature p-type Microcrystalline Silicon as Carrier Selective Contact for Silicon Heterojunction Solar Cells

Silicon heterojunction (SHJ) solar cells have reached record efficiency, particularly in all-back-contacted architectures. Despite this, two-side contacted SHJ cells still suffer from parasitic absorption and series resistance losses in the amorphous silicon contacts. An alternative to the doped amorphous silicon layer is microcrystalline silicon, which exhibits improved transparency and charge transport while maintaining the superior passivation quality of all-silicon contact stacks. However, depositing thin, highly crystalline films has remained a challenge until recently. In this work, we use deposition temperatures <200 ◦C to improve the performance of p-type µc-Si:H contact layers. With these layers, we demonstrate Jsc gains of 1 mA/cm2, while reducing series resistance below 1 Ωcm2, leading to screenprinted 4 cm2 cells with certified η = 23:45%. Using a suite of device and material characterization techniques, we show that reduced deposition temperature leads to an increase in crystalline volume fraction from 35% to 55% for p-type films, which mitigates parasitic absorption in the front contact and facilitates hole extraction. These improvements are explained as resulting from higher transparency in the p-type layer accompanied by higher band bending in the c-Si wafer. These findings provide a method to improve SHJ solar cells performance, while offering insight into the importance of band bending considerations when optimizing heterojunction designs

Improved Optics in Monolithic Perovskite/Silicon Tandem Solar Cells with a Nanocrystalline Silicon Recombination Junction

Perovskite/silicon tandem solar cells are increasingly recognized as promi-sing candidates for next-generation photovoltaics with performance beyond the single-junction limit at potentially low production costs. Current designs for monolithic tandems rely on transparent conductive oxides as an intermediate recombination layer, which lead to optical losses and reduced shunt resistance. An improved recombination junction based on nanocrystalline silicon layers to mitigate these losses is demonstrated. When employed in monolithic perovskite/silicon heterojunction tandem cells with a planar front side, this junction is found to increase the bottom cell photocurrent by more than 1 mA cm -2 . In combination with a cesium-based perovskite top cell, this leads to tandem cell power-conversion efficiencies of up to 22.7% obtained from J-V measurements and steady-state efficiencies of up to 22.0% during maximum power point tracking. Thanks to its low lateral conductivity, the nanocrystalline silicon recombination junction enables upscaling of monolithic perovskite/silicon heterojunction tandem cells, resulting in a 12.96 cm 2 monolithic tandem cell with a steady-state efficiency of 18%