Comparison of TiO₂and other dielectric coatings for buried‐contact solar cells: a review

Abstract

This paper compares the optical, electronic, physical and chemical properties of dielectric thin films that are commonly used to enhance the performance of bulk silicon photovoltaic devices. The standard buried‐contact (BC) solar cell presents a particularly challenging set of criteria, requiring the dielectric film to act as: (i) an anti‐reflection (AR) coating; (ii) a film compatible with surface passivation; (iii) a mask for an electroless metal plating step; (iv) a diffusion barrier for achieving a selective emitter; (v) a film with excellent chemical resistance; (vi) a stable layer during high‐temperature processing. The dielectric coatings reviewed here include thermally grown silicon dioxide (SiO2), silicon nitride deposited by plasma‐enhanced chemical vapour deposition (a‐SiNx:H) and low‐pressure chemical vapour deposition (Si3N4), silicon oxynitride (SiON), cerium dioxide (CeO2), zinc sulphide (ZnS), and titanium dioxide (TiO2). While TiO2 dielectric coatings exhibit the best optical performance and a simple post‐deposition surface passivation sequence has been developed, they require an additional sacrificial diffusion barrier to survive the heavy groove diffusion step. A‐SiNx:H affords passivation through its high fixed positive charge density and large hydrogen concentration; however, it is difficult to retain these electronic benefits during lengthy high‐temperature processing. Therefore, for the BC solar cell, Si3N4 films would appear to be the best choice of dielectric films common in industrial use. Copyright © 2004 John Wiley & Sons, Ltd.

Totally Vacuum-Free Processed Crystalline Silicon Solar Cells over 17.5% Conversion Efficiency

“…ARC films are commonly used on the surface of textured cells to reduce the reflectivity further and to improve the photo current which leads to improving the efficiency of the solar cell. SiN x films or SiN x based stack layers are commonly used in the commercial solar cells for ARC purposes with their effective antireflective behavior and good passivation effect [7,8]. However, its deposition technique of plasma-enhanced chemical vapor deposition (PECVD) [9,10] has some drawbacks, including the need for toxic and hazardous gases such as SiH 4 and NH 3 with vacuum processing for chemical vapor deposition operation, difficult handling, and high costs.…”

Effect of topological disorder on structural, mechanical, and electronic properties of amorphous silicon nitride: An atomistic study

“…1 In addition to their use in silicon-oxide-nitride-oxide-silicon (SONOS) structures for non-volatile memory applications, 2 they are also widely used as a dielectric in radio frequency Microelectromechanical system (RF-MEMS) switches, [3][4][5] anti-reflective coating in silicon solar cells, 6,7 passivation layer to form alkali-ion diffusion barrier 7 and dielectric insulator film for thin film transistors (TFT). 8 The amorphous SiN x matrix is highly constrained due to its high overall coordination number and, hence, exhibits a high concentration of defects as compared to other amorphous dielectrics such as a-SiO 2 .…”

Omnidirectional antireflective properties of porous tungsten oxide films with in-depth variation of void fraction and stoichiometry

“…In the case of inverse pyramid-like textured Si substrate, routinely used in Si solar cells manufacturing, an ARC coating such as the one described above will cause further decrease of the reflection seen in Fig. 1(b) and (c), as, e.g., shown for the case of TiO 2 ARC [11]. For cells operating under suntracking this will decrease the requirements of the tracker for precision and therefore its price, which is related to the total price of the electricity produced.…”

“…Thin films exhibiting thickness-graded refractive index profiles are being intensively studied recently, for applications in antireflective coatings with enhanced omnidirectionality and broadband characteristics [4]. The refractive index profile and hence the reflection suppression, is controlled either by depositing layers of different materials or by controlling the in-depth void fraction variation using multiple deposition steps, by employing various types of lithography and subsequent pattern transfer such as plasma etching, by incorporating particles and properly tuned deposition processes etc [5][6][7][8][9][10][11]. Even though most of these coatings exhibit good AR performance, the scale-up and the integration of most of these processes are either difficult or subject to serious economic constraints.…”