Adrien Bidiville

High-efficiency amorphous silicon solar cells: Impact of deposition rate on metastability

Hydrogenated amorphous silicon (a-Si:H) films, used for light absorbers of p-i-n solar cells, were deposited at various deposition rates (Rd) ranging over two orders of magnitude (Rd ∼ 2 × 10−3–3 × 10−1 nm/s) by using diode and triode plasma-enhanced chemical vapor deposition (PECVD). The impact of varying Rd on the light-soaking stability of the solar cells has been investigated. Although a reduction of Rd mitigates the light-induced degradation in the typical range of Rd (>10−1 nm/s), it remains present even in the very low Rd (<10−2 nm/s), indicating that the metastable effect persists in a-Si:H regardless of Rd. The best performing cell, whose a-Si:H absorber is characterized by low amount of metastable defect and high bandgap, can be obtained at Rd of ∼1–3 × 10−2 nm/s by triode PECVD. By applying such a-Si:H in the improved p-i-n devices, we demonstrate two record independently confirmed stabilized efficiencies of 10.22% for single-junction and 12.69% for a-Si:H/hydrogenated microcrystalline silicon ...

High-efficiency thin-film silicon solar cells realized by integrating stable a-Si:H absorbers into improved device design

We report that thin-film silicon solar cells exhibiting high stabilized efficiencies can be obtained by depositing hydrogenated amorphous silicon (a-Si:H) absorbers using triode-type plasma-enhanced chemical vapor deposition. The improved light-soaking stability and performance of solar cells are also realized by optimizing the device design, such as p and p–i buffer layers. As a result, we attain independently confirmed stabilized efficiencies of 10.1–10.2% for a-Si:H single-junction solar cells (absorber thickness: ti = 220–310 nm) and 12.69% for an a-Si:H (ti = 350 nm)/hydrogenated microcrystalline silicon (µc-Si:H) tandem solar cell fabricated using textured SnO2 and ZnO substrates, respectively. The relative efficiency degradations of these solar cells are ~10 and 3%, respectively, under 1 sun illumination at 50 °C for 1000 h.

Effect of oxygen doping in microcrystalline SiGe p-i-n solar cells

The effect of doping with oxygen the microcrystalline silicon-germanium absorber layer of single-junction p-i-n solar cells has been studied. In parallel, the absorber layer quality was measured by depositing absorber layers directly on glass and measuring their electrical properties. By doping the absorber layer with the optimum oxygen concentration (about 1.4×1019 cm−3), an increase in short-circuit current density of almost 4 mA/cm2 was achieved in 3 μm thick p-i-n solar cell. This effect is attributed to the oxygen doping compensating the space charges caused by the germanium dangling bonds rather than the direct defect passivation, as no drastic change in layer quality was measured.

Analysis of bulk and interface defects in hydrogenated amorphous silicon solar cells by Fourier transform photocurrent spectroscopy

A series of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells with varying absorber thicknesses (ti = 10–500 nm) were investigated by Fourier transform photocurrent spectroscopy to determine the sub-bandgap absorption originating from the native and metastable defects. Differences between annealed and degraded states of a-Si:H solar cells, as well as between diode and triode plasma-enhanced chemical vapor deposition methods for the absorber layer depositions were analyzed. Despite having a comparable annealed state performance to diode-deposited cells, the triode-deposited a-Si:H solar cells exhibit notably less light-induced metastable defects over the whole range of absorber thickness. Furthermore, the analysis of thin solar cells (ti < 100 nm) suggests that defects are not preferentially present at the interfaces of the intrinsic layer, but that there are regions with a higher absorption coefficient than the bulk of the absorber near the doped layers. Finally, we show that the solar cell perfor...

Role of the Fermi level in the formation of electronic band-tails and mid-gap states of hydrogenated amorphous silicon in thin-film solar cells

Hydrogenated amorphous silicon solar cells in p-i-n and n-i-p configurations were made with the intrinsic absorber layer deposited at different temperatures, between 200 and 350 °C. Using Fourier-transform photocurrent spectroscopy, the sub-gap absorption was measured, allowing the evaluation of the band-tail width and mid-gap defect quantity of the intrinsic absorber layer of the working device. When deposited at high temperature (>200 °C), p-i-n cells showed a larger performance decrease than n-i-p cells, along with broader band-tails as well as a larger number of defects created in the absorber layer. Hydrogen content measurements showed that for high temperature deposition (>200 °C), the Si-H bond becomes markedly less stable if the Fermi level of the intrinsic layer is shifted toward the valence band by an adjacent p-layer. Furthermore, by annealing samples at different stages of their layer stack deposition, the impact of the band-tail and mid-gap defect states on the open-circuit voltage and on the...