Superior Phosphorous Doping in Nanocrystalline Silicon Thin Films and Their Application as Emitter Layers in Silicon Heterojunction Solar Cells

Abstract

Phosphorous doping in the nc-Si network induces gradually reduced crystallinity; however, preferential growth along <220>-oriented crystallites promotes the columnar-like growth morphology. At optimum doping, substitution by donor P+-atoms in the c-Si lattice contributes surplus free electrons and high carrier mobility, resulting in superior electrical conductivity in the n-nc-Si network. An elevated doping leads to incorporating elemental P0 atoms in the interstitial position or forming P–Si–H clusters and generating voids between the crystalline columns. Segregation of defects contributes to decreasing carrier mobility and reducing conductivity after diminishing crystallinity and narrowing the optical band gap. By precisely controlling the growth at 250 °C and efficient electrically active doping by P+-atoms, n-nc-Si thin films with superior dark conductivity (∼101 S cm–1) are produced in which the percolation of charge carriers through the crystalline columns could facilitate stacked-layer devices. The optimum n-nc-Si thin films are used as the emitter layers in n-nc-Si/p-c-Si heterojunction solar cells (HJSCs). Furthermore, an ultrathin a-Si:H buffer layer on the p-c-Si minimizes the junction carrier recombination loss, and subsequent postdeposition short-time H-plasma treatment (PSHPT) ensures seeds for superior nanocrystallization in the n-nc-Si emitter layer. The n-nc-Si/(PSHPT)i-nc-Si­(buffer layer)/p-c-Si HJSC delivers a PV conversion efficiency, η ∼12.35%, via a reasonable fill factor of ∼0.647 and sensible JSC of ∼32.75 mA cm–2. Further improvement in the PV performance could be possible using suitably thinner p-c-Si wafers, harmonizing with the effective carrier diffusion length, and fabricating a high-quality passivation structure on the backside.

Growth Mechanism and Opto-Structural Characterization of Vertically Oriented Si Nanowires: Implications for Heterojunction Solar Cells

“…Later, four additional HJSCs (HJSC7–10) were developed in p / i / n core/shell geometry, where the intrinsic Si ( i -Si) shell coating was introduced in between its earlier p -shell layer and the n -core of the p / n configuration, following suitable materials characteristics as optimized for solar cells in a few prior publications of this laboratory (growth conditions for both p - and i -shells are listed in Table ). − …”

“…The cleaned SiNW arrays were utilized in the fabrication of p / n and p / i / n HJSCs in the core/shell configuration. The specific shell layers of HJSCs were developed following growth conditions optimized in our numerous earlier publications concerning the fabrication of solar cells, as listed in Table in Section of the present article. − The plasma exposed area of the SiNW array samples during shell deposition was restricted to (1.5 × 1.5) cm 2 using steel masks attached to the substrate holder. For better charge collection during the functioning of the solar cells, a thin Sn-doped In 2 O 3 (ITO) film of thickness ∼80 nm and area ∼(1 × 1) cm 2 was grown on top of the p -layer by sputtering from an ITO target.…”

Investigating the Ag-assisted Chemical Etching Kinetics in Growing Si-NWs and Fabricating the p-i-n core–shell Heterojunction Si-NW Array Solar Cells

“…The freshly prepared chemically etched n -type c-Si-NWs samples were immediately transferred into an RF-PECVD chamber, where the NW surface was cleaned by a rapid in situ H 2 plasma treatment for 3 min. The different layers of the proposed Si-NW HJSCs were grown based on detailed characterization of the material done in our several previous publications and its use in the fabrication of solar cells. − The growth conditions are listed in Table .…”

Structural and optical properties of phosphorous doped nanocrystalline silicon deposited using a VHF PECVD process for silicon heterojunction solar cells and optimization of a simple p–n junction cell using SCAP-1D tool

“… 9 However a-Si:H has been widely used in heterojunction (HIT) solar cells both as passivating and emitter layer and the use of n-doped μc/nc-Si:H has also shown excellent result as an emitter layer in HIT solar cells. 10 …”

“…Scientists have used different techniques to obtain good quality n type nc-Si:H films under controlled doping such as plasma enhanced chemical vapor deposition (PECVD), microwave PECVD, 12 electron beam evaporation, 13 electron cyclotron resonance PECVD, 14 Si ion implantation, 15 hot wire CVD, 16 cathodic vacuum arc, 17 RF magnetron sputtering 18 etc. Furthermore, in case of selection of wafer, n type possess lower defect density, low recombination rate of charge carriers at the interface and even high resistance against degradation 10 than p type wafer. But the major concern is high production cost of n type ingots and hence less availability in the market.…”