Energy-harvesting photovoltaic transparent tandem devices using hydrogenated amorphous and microcrystalline silicon absorber layers for window applications

Abstract

Transparent photovoltaic (TPV) tandem devices were prepared via plasma-enhanced chemical vapor deposition, using hydrogenated amorphous (a-Si:H) and microcrystalline (mc-Si:H) absorber layers that were sandwiched by transparent conducting oxide (TCO) electrodes. The high-performance TPV tandem devices were designed by controlling the film thickness of the mc-Si:H absorbers. For the TPV tandem devices with 300-nm-thick a-Si:H top cells, increasing the absorber thickness (tbottom) of mc-Si:H bottom cells from 1.0 to 2.1 μm induced an increase in power conversion efficiencies (PCEs) from 6.5% to 8.3% with a minor decrease in the average light transmittance from 16.6% to 14.6% at the 500–800 nm wavelengths. The TPV tandem devices exhibited JSC gains from 4.3 mA cm−2 (tbottom = 1.0 μm) to 0.5 mA cm−2 (tbottom = 2.3 μm) under bifacial illumination (front: 100 mW cm−2 and rear: 30 mW cm−2). This further resulted in additional PCE gains from 2.8% (tbottom = 1.0 μm) to 0.4% (tbottom = 2.3 μm), in comparison to the corresponding samples under front illumination only. The TPV tandem devices demonstrated excellent PV performance even at low-light illumination intensities (∼21 mW cm−2) in comparison to those at standard illumination light intensity (100 mW cm−2), while maintaining PCE values as high as 80%.