Fabrication and characterization of Al2O3 /Si composite nanodome structures for high efficiency crystalline Si thin film solar cells

Abstract

We report on our fabrication and characterization of Al2O3/Si composite nanodome (CND) structures, which is composed of Si nanodome structures with a conformal cladding Al2O3 layer to evaluate its optical and electrical performance when it is applied to thin film solar cells. It has been observed that by application of Al2O3thin film coating using atomic layer deposition (ALD) to the Si nanodome structures, both optical and electrical performances are greatly improved. The reflectivity of less than 3% over the wavelength range of from 200 nm to 2000 nm at an incident angle from 0° to 45° is achieved when the Al2O3 film is 90 nm thick. The ultimate efficiency of around 27% is obtained on the CND textured 2 μm-thick Si solar cells, which is compared to the efficiency of around 25.75% and 15% for the 2 μm-thick Si nanodome surface-decorated and planar samples respectively. Electrical characterization was made by using CND-decorated MOS devices to measure device’s leakage current and capacitance dispersion. It is found the electrical performance is sensitive to the thickness of the Al2O3 film, and the performance is remarkably improved when the dielectric layer thickness is 90 nm thick. The leakage current, which is less than 4x10−9 A/cm2 over voltage range of from -3 V to 3 V, is reduced by several orders of magnitude. C-V measurements also shows as small as 0.3% of variation in the capacitance over the frequency range from 10 kHz to 500 kHz, which is a strong indication of surface states being fully passivated. TEM examination of CND-decorated samples also reveals the occurrence of SiOx layer formed between the interface of Si and the Al2O3 film, which is thin enough that ensures the presence of field-effect passivation, From our theoretical and experimental study, we believe Al2O3 coated CND structures is a truly viable approach to achieving higher device efficiency.

Green upconversion improvement of TiO2 codoped Er3+-Yb3+ nanoparticles based thin film by adding ALD-Al2O3 for silicon solar cell applications

“…. 3) demonstrate that using thicker layer of Al 2 O 3 reduces the reflectance of the structure especially at 950 nm (decreasing of about 54%), which is the same wavelength as the excitation source, so increasing the absorption of photons which lead to an increase of upconversion emission. The reflection value on the 400 to 1100 nm spectrum range is highly desirable as it can lead to the absorption enhancement in thin film solar cells [50]. A structure with these properties would increase the solar cell efficiency combining upconversion and anti-reflectivity, which is similar to as recently reported in [8].…”

“…For Yb 2 O 3 , it absorbs and emits at 980 nm, the emitted photons can probably be reabsorbed after that by codoped TiO 2 or even by Er 2 O 3 . For Er 2 O 3 , the Er 3+ ion alone can achieve luminescence without the requirement of a sensitizer that means no ETU process is present (weak efficiency compared to when using a sensitizer) [50]. The energy of the 980 nm matches the absorption energy level between 4 I 15/2 ground state and 4 I 11/2 excitation state of Er 3+ .…”

Lithography‐Free Method to Synthesize Quasiperiodic Silicon Inverted‐Pyramid Arrays: A Broadband Light Trapper for High‐Efficiency Thin Silicon Solar Cells

“…[ 9–12 ] For this purpose, excellent light trapping is the most important requirement. Several important light‐trapping mechanisms in silicon have been proposed, e.g., nanowires arrays, [ 13–19 ] nanospheres assembly, [ 20 ] nanodome, [ 21 ] nanocone, [ 22 ] nano/micropore arrays, [ 23–27 ] nanopyramid arrays, [ 28–34 ] and inverted‐pyramid arrays (IPAs). [ 9–12,35–40 ]…”

“…[9][10][11][12] For this purpose, excellent light trapping is the most important requirement. Several important light-trapping mechanisms in silicon have been proposed, e.g., nanowires arrays, [13][14][15][16][17][18][19] nanospheres assembly, [20] nanodome, [21] nanocone, [22] nano/micropore arrays, [23][24][25][26][27] nanopyramid arrays, [28][29][30][31][32][33][34] and inverted-pyramid arrays (IPAs). [9][10][11][12][35][36][37][38][39][40] Although several light-trapping mechanisms are proposed and adopted by different groups of scientists, major successes are achieved on nano/micropyramid arrays, nanohole arrays, and IPAs.…”