High-Quality Amorphous-Crystalline Silicon Heterostructures Using the Grid-Based Triode Radio-Frequency Plasma Enhanced Chemical Vapour Deposition Method.

摘要

The amorphous-crystalline silicon heterojunction (SHJ) represents a new paradigm in crystalline silicon (c-Si) photovoltaics (PV). To achieve the 27% efficiency target for SHJ PV, defects in the silicon heterointerface must be minimized by growing high-quality hydrogenated amorphous silicon (a-Si:H) onto the c-Si surfaces without deposition-related damage. Typically, a-Si:H is deposited using radio-frequency (RF) plasma enhanced chemical vapour deposition (PECVD), which in its conventional configuration directly exposes the c-Si growth surface to the ignited plasma. In this thesis, silicon heterostructures prepared by the grid-based triode RF PECVD method is investigated for the first time. The triode method allows for high-quality a-Si:H growth with the c-Si surfaces shielded from any potential plasma damage.;Using a custom-built configurable PECVD facility, a systematic study was conducted and it was demonstrated that the triode method affords the preparation of a-Si:H with excellent bulk film quality and state-of-the-art passivation for c-Si surfaces. Using the triode method, an effective minority carrier lifetime (taueff) of 8.1 ms and an Auger-corrected surface recombination velocity (S) of 2.4 cm/s at an excess carrier density of 1015 cm-3 have been achieved for 1-2 ohm-cm n-type c-Si passivated with intrinsic a-Si:H. Further, using the triode method to deposit thin-layers of intrinsic and doped a-Si:H, a conventional SHJ solar cell structure was prepared and was found to exhibit an excellent implied Voc of 710 mV.;Under all conditions scanned, samples prepared in the triode configuration showed improved passivation compared with samples prepared in the conventional diode configuration with the best triode prepared sample showing a nearly threefold increase in taueff and a twofold decrease in S compared with the best diode prepared sample. Furthermore, a-Si:H deposited using the triode method showed significantly improved bulk properties compared to diode prepared samples with a 30% to 50% reduction in microstructural parameter for intrinsic a-Si:H and a greater than 10% reduction in activation energy for p-type a-Si:H.;Through examination of the photostability of triode prepared samples, the unique metastability properties of the a-Si:H - c-Si heterointerface was discovered and a relationship describing the degree and kinetics of light-induced change in the heterointerface was uncovered.