Low-Temperature, Chemically Grown Titanium Oxide Thin Films with a High Hole Tunneling Rate for Si Solar Cells

Abstract

Abstract:In this paper, we propose a chemically grown titanium oxide (TiO 2 ) on Si to form a heterojunction for photovoltaic devices. The chemically grown TiO 2 does not block hole transport. Ultraviolet photoemission spectroscopy was used to study the band alignment. A substantial band offset at the TiO 2 /Si interface was observed. X-ray photoemission spectroscopy (XPS) revealed that the chemically grown TiO 2 is oxygen-deficient and contains numerous gap states. A multiple-trap-assisted tunneling (TAT) model was used to explain the high hole injection rate. According to this model, the tunneling rate can be 10 5 orders of magnitude higher for holes passing through TiO 2 than for flow through SiO 2 . With 24-nm-thick TiO 2 , a Si solar cell achieves a 33.2 mA/cm 2 photocurrent on a planar substrate, with a 9.4% power conversion efficiency. Plan-view scanning electron microscopy images indicate that a moth-eye-like structure formed during TiO 2 deposition. This structure enables light harvesting for a high photocurrent. The high photocurrent and ease of production of chemically grown TiO 2 imply that it is a suitable candidate for future low-cost, high-efficiency solar cell applications.

Hybrid porous silicon/silver nanostructures for the development of enhanced photovoltaic devices

“…In particular, the use of TiO2 thin films has the great advantage of serving at the same time as passivation layers to prevent nanoPS from oxidation and to increase the open-circuit voltage. At the same time, the TiO2 thin films can be used as antireflective coatings [22].…”

Solution-Processed Titanium Oxide for Rear Contact Improvement in Heterojunction Solar Cells

“…The titanium oxide with empty and filled band edges at 4 eV and 7.2 eV below the vacuum level, respectively. Furthermore, the Fermi energy of the LPD-TiO x layer is 4.2 eV [3]. The conduction band and valence edges are 3.9~4.0 and 5.6~5.7 eV for amorphous silicon (a-Si:H) adopted from literature [20,21].…”

“…After that, the front surface was passivated with photoresist for rear-side TiO x deposition. The TiO x was deposited in 8, 16, and 25 nm thicknesses by a LPD method, details of which were published previously [2,3]. (NH 4 ) 2 TiF 6 solution and H 3 BO 3 were used as precursors.…”

“…With appropriate band alignment to Si, the sub-stoichiometric transition metal oxides (TMOs) [1], such as titanium oxide (TiO x ) [2][3][4], molybdenum oxide (MoO x ) [5], and nickel oxide (NiO x ) [6], have been investigated as either an electron-selective or a hole-selective contact in silicon solar cells. Conventionally, the ohmic contacts in Si were fabricated by depositing metals on a heavily-doped region, which is expensive and complex for Si solar cells.…”

Wet Chemical Oxidation to Improve Interfacial Properties of Al2O3/Si and Interface Analysis of Al2O3/SiOx/Si Structure Using Surface Carrier Lifetime Simulation and Capacitance–Voltage Measurement

“…The surface passivation of crystalline silicon (c-Si) solar cells can be improved using various materials such as SiO 2 [1][2][3][4][5][6], SiN x [7][8][9], Al 2 O 3 [10][11][12][13], TiO x [14][15][16], MoO x [17,18], and poly-Si [19][20][21][22]. In particular, Al 2 O 3 thin films are most widely used for boron-doped Si surfaces (or p + emitter surfaces) owing to the low surface recombination velocity (SRV) [10,11].…”