Comparison of amorphous silicon absorber materials: Light-induced degradation and solar cell efficiency

Several amorphous silicon (a-Si:H) deposition conditions have been reported to produce films that degrade least under light soaking when incorporated into a-Si:H solar cells. However, a systematic comparison of these a-Si:H materials has never been presented. In the present study, different plasma-enhanced chemical vapor deposition conditions, yielding standard low-pressure VHF a-Si:H, protocrystalline, polymorphous, and high-pressure RF a-Si:H materials, are compared with respect to their optical properties and their behavior when incorporated into single-junction solar cells. A wide deposition parameter space has been explored in the same deposition system varying hydrogen dilution, deposition pressure, temperature, frequency, and power. From the physics of layer growth, to layer properties, to solar cell performance and light-induced degradation, a consistent picture of a-Si:H materials that are currently used for a-Si:H solar cells emerges. The applications of these materials in single-junction, tandem, and triple-junction solar cells are discussed, as well as their deposition compatibility with rough substrates, taking into account aspects of voltage, current, and charge collection. In sum, this contributes to answering the question, “Which material is best for which type of solar cell?”