W.M.M. Kessels

High efficiency n-type Si solar cells on Al2O3-passivated boron emitters

In order to utilize the full potential of solar cells fabricated on n-type silicon, it is necessary to achieve an excellent passivation on B-doped emitters. Experimental studies on test structures and theoretical considerations have shown that a negatively charged dielectric layer would be ideally suited for this purpose. Thus, in this work the negative-charge dielectric Al2O3 was applied as surface passivation layer on high-efficiency n-type silicon solar cells. With this front surface passivation layer, a confirmed conversion efficiency of 23.2% was achieved. For the open-circuit voltage Voc of 703.6mV, the upper limit for the emitter saturation current density J0e, including the metalized area, has been evaluated to be 29fA∕cm2. This clearly shows that an excellent passivation of highly doped p-type c-Si can be obtained at the device level by applying Al2O3.

Plasma-assisted atomic layer deposition of Al2O3 moisture permeation barriers on polymers

Thin Al2O3 films of different thicknesses (10–40nm) were deposited by plasma-assisted atomic layer deposition on substrates of poly(2,6-ethylenenaphthalate) (PEN), and the water vapor transmission rate (WVTR) values were measured by means of the calcium test. The permeation barrier properties improved with decreasing substrate temperature and a good WVTR of 5×10−3gm−2day−1 (WVTRPEN=0.5gm−2day−1) was measured for a 20nm thick Al2O3 film deposited at room temperature using short purging times. Such ultrathin, low-temperature deposited, high-quality moisture permeation barriers are an essential requirement for the implementation of polymeric substrates in flexible electronic and display applications.

Effective passivation of Si surfaces by plasma deposited SiOx/a-SiNx:H stacks

Very low surface recombination velocities 6 and 11 cm / s were obtained for SiO x / a -SiN x : H stacks synthesized by plasma-enhanced chemical vapor deposition on low resistivity n - and p -type c -Si , respectively. The stacks induced a constant effective lifetime under low illumination, comparable to Al 2 O 3 on p -type Si. Compared to single layer a -SiN x : H , a lower positive fixed charge density was revealed by second-harmonic generation measurements, while field-effect passivation was absent for a reference stack comprising thermally grown SiO 2 . The results indicate that hydrogenation of interface states played a key role in the passivation and remained effective up to annealing temperatures > 800 ° C .

High-rate plasma-deposited SiO2 films for surface passivation of crystalline silicon

SiO2 films were deposited by means of the expanding thermal plasma technique at rates in the range of 0.4–1.4μm∕min using an argon∕oxygen∕octamethylcyclotetrasiloxane (OMCTS) gas mixture. The film composition was studied by means of various optical and nuclear profiling techniques. The films deposited with a low OMCTS to oxygen ratio showed no residual carbon and a low hydrogen content of ∼2% with a refractive index close to thermal oxide. For a higher OMCTS to oxygen ratio a carbon content of ∼4% was detected in the films and the refractive index increased to 1.67. The surface passivation of the SiO2 films was tested on high quality crystalline silicon. The films yielded an excellent level of surface passivation for plasma-deposited SiO2 films with an effective surface recombination velocity of 54cm∕s on 1.3Ωcm n-type float zone crystalline silicon substrates after a 15min forming gas anneal at 600°C.

Cathode encapsulation of organic light emitting diodes by atomic layer deposited Al2O3 films and Al2O3/a-SiNx: H stacks

Al2O3 thin films synthesized by plasma-enhanced atomic layer deposition (ALD) at room temperature (25 °C) have been tested as water vapor permeation barriers for organic light emitting diode devices. Silicon nitride films (a-SiNx:H) deposited by plasma-enhanced chemical vapor deposition served as reference and were used to develop Al2O3/a-SiNx:H stacks. On the basis of Ca test measurements, a very low intrinsic water vapor transmission rate of ≤ 2 × 10−6 g m−2 day−1 and 4 × 10−6 g m−2 day−1 (20 oC/50% relative humidity) were found for 20–40 nm Al2O3 and 300 nm a-SiNx:H films, respectively. The cathode particle coverage was a factor of 4 better for the Al2O3 films compared to the a-SiNx:H films and an average of 0.12 defects per cm2 was obtained for a stack consisting of three barrier layers (Al2O3/a-SiNx:H/Al2O3).

Plasma-enhanced and thermal atomic layer deposition of Al2O3 using dimethylaluminum isopropoxide, [Al(CH3)2(μ-OiPr)]2, as an alternative aluminum precursor

The authors have been investigating the use of [Al(CH3)2(μ-OiPr)]2 (DMAI) as an alternative Al precursor to [Al(CH3)3] (TMA) for remote plasma-enhanced and thermal ALD over wide temperature ranges of 25–400 and 100–400 °C, respectively. The growth per cycle (GPC) obtained using in situ spectroscopic ellipsometry for plasma-enhanced ALD was 0.7–0.9 A/cycle, generally lower than the >0.9 A/cycle afforded by TMA. In contrast, the thermal process gave a higher GPC than TMA above 250 °C, but below this temperature, the GPC decreased rapidly with decreasing temperature. Quadrupole mass spectrometry data confirmed that both CH4 and HOiPr were formed during the DMAI dose for both the plasma-enhanced and thermal processes. CH4 and HOiPr were also formed during the H2O dose but combustion-like products (CO2 and H2O) were observed during the O2 plasma dose. Rutherford backscattering spectrometry showed that, for temperatures >100 °C and >200 °C for plasma-enhanced and thermal ALD, respectively, films from DMAI had a...

Silicon passivation and tunneling contact formation by atomic layer deposited Al2O3/ZnO stacks

The passivation of Si by Al2O3/ZnO stacks, which can serve as passivated tunneling contacts or heterojunctions in silicon photovoltaics, was investigated. It was demonstrated that stacks with Al2O3 thicknesses >3 nm lead to lower surface recombination velocities (Seff,max < 4c m s −1 )o n n- and p-type Si than single-layer Al2O3 films for a wide range of ZnO thicknesses and irrespective of Al-doping of the ZnO. Stacks with an Al2O3 thickness of 1‐2 nm were found to combine reasonable surface passivation (Seff,max = 100‐700 cm s −1 ) with sufficiently high tunneling current densities (10‐300 mA cm −2 at 700 mV).

Atomic-layer-deposited aluminum oxide for the surface passivation of high-efficiency silicon solar cells

We present independently confirmed efficiencies above 20% for PERC-type solar cells with the point-contacted rear being either passivated by atomic-layer-deposited Al<inf>2</inf>O<inf>3</inf> or by stacks consisting of an ultrathin Al<inf>2</inf>O<inf>3</inf> film and a thicker PECVD-SiO<inf>x</inf> layer. Internal quantum efficiency measurements reveal that the effective rear surface recombination velocities of the single-layer Al<inf>2</inf>O<inf>3</inf>-passivated cells are comparable to those measured on reference cells passivated by an aluminum-annealed thermal SiO<inf>2</inf>, while those of the Al<inf>2</inf>O<inf>3</inf>/SiOx-passivated cells are even lower. Very low effective rear surface recombination velocities of only 70 cm/s are reported for the Al<inf>2</inf>O<inf>3</inf>/SiO<inf>x</inf> stacks, including metalized areas on the cell rear.

Hydrogen in a-Si:H deposited by an expanding thermal plasma : a temperature, growth rate and isotope study

The hydrogen and silicon density of a-Si:H-films deposited by an expanding thermal plasma have been investigated for a wide range of substrate temperatures and growth rates by infrared absorption spectroscopy in combination with elastic recoil detection and Rutherford backscattering. The study reveals that, despite the increasing atomic hydrogen interaction and high substrate temperatures, the a-Si:H remains purely amorphous at low growth rates as concluded from Raman spectroscopy. Additionally, the infrared spectroscopy proportionality constants of the silicon-hydrogen and silicon-deuterium bondings have been recalibrated.

A model for the deposition of a-C:H using an expanding thermal arc

Abstract Amorphous hydrogenated carbon films have been deposited at high growth rates (10–70 nm/s) by seeding acetylene in an expanding thermal argon plasma. The influence of the substrate temperature in the range of −50–300°C on the film properties, e.g. refractive index, hydrogen content and the growth rate, has been investigated. From this, in combination with earlier results, a first attempt at a qualitative deposition model is given.