Optimization of hydrogenated amorphous silicon p–i–n solar cells with two-step i layers guided by real-time spectroscopic ellipsometry

Abstract

Hydrogenated amorphous silicon (a-Si:H) p–i–n solar cell performance has been optimized using a two-step i-layer growth process. This effort has been guided by real-time spectroscopic ellipsometry (RTSE) studies of the nucleation and growth of a-Si:H films by plasma-enhanced chemical vapor deposition at 200 °C using a variable H2-dilution gas flow ratio R=[H2]/[SiH4]. RTSE studies during film growth with R>15 reveal a transition from the amorphous to microcrystalline (a→μc) phase at a critical thickness that decreases with increasing R. From such results, the optimum two-step process was designed such that the initial stage of the i layer (∼200 Å) is deposited at much higher R than the bulk to ensure that the film remains within the amorphous side of the a→μc phase boundary, yet as close as possible to this boundary at low i-layer thicknesses.

Evolution of the microstructure in microcrystalline silicon prepared by very high frequency glow-discharge using hydrogen dilution

“…13 Thus, care has to be taken when transferring our observations to layers grown on other substrates. In particular, our observations of the variety of microstructures grown on glass substrates call now for the study of the microstructure of intrinsic c-Si:H layers grown within p-i-n devices.…”

Optimization of amorphous silicon thin film solar cells for flexible photovoltaics

“…The buffer layer is highly diluted with H 2 which promotes a better quality and a higher band gap material. 18,21,22 In Sec. III D, we demonstrated that the buffer layer improves slightly the V oc and reduces mainly the series resistance of the a-Si: H solar cell and thus improves the FF of the a-Si: H solar cell.…”

“…It increases the band gap of a-Si: H, which should act as a graded interface between the i-layer and the n-SiC layer, and reduces the density of defects at the n / i interface. 18,21,22 Figure 10 shows the efficiencies of the cell with and without buffer layer for different surface treatment times on the ZnO LP-CVD. Table II the buffer layer is mostly in FF ͑63.4% ⇒ 67.6%͒ and slightly in V oc ͑885 mV⇒ 895 mV͒.…”

From amorphous to microcrystalline silicon: Moving from one to the other by halogenated silicon plasma chemistry

“…The life-motif of improving stability against photodegradation of a-Si:H led researchers to demonstrate recently that "protocrystalline Si", produced near the amorphous-to-microcrystalline silicon transition regime, exhibits a higher degree of ordering with increased stability under light illumination [14][15][16][17][18][19].…”

“…[15][16][17][22][23][24][25][26] or without H 2 dilution [27][28][29][30][31][32][33][34], in the course of years various halogenated Si gas precursors, e.g. SiF 4 [35][36][37][38][39][40], SiCl 4 [41][42][43], and SiH 2 Cl 2 [44,45] have also been investigated and reported.…”