Stephan Suckow | RWTH Aachen University (original) (raw)

Papers by Stephan Suckow

Solar Energy Materials and Solar Cells, 2016

2011 37th IEEE Photovoltaic Specialists Conference, 2011

ABSTRACT The current-voltage (I-V) characteristics of processed industrial multicrystalline silic... more ABSTRACT The current-voltage (I-V) characteristics of processed industrial multicrystalline silicon (mc-Si) solar cells usually vary within a narrow range (e.g. +/−1 % abs. efficiency). Nevertheless, occasionally cells with very low efficiencies are produced with loss mechanisms such as local shunts or areas with unusually high recombination. In this paper we investigated industrial mc-Si solar cells with exceptionally low efficiencies in detail by dark and illuminated I-V measurements followed by an analysis based on the two-diode-model to determine the dominant electrical loss mechanisms. Subsequently spatially-resolved lock-in thermography (LIT) measurements were used to localise defect positions in these solar cells. These defects were electrically isolated with a laser. The solar cells were characterised again using the same analysis methods. For shunted cells an efficiency gain of up to 2.4 % absolute was obtained and the shunts disappeared. A detailed investigation of I-V data before and after laser isolation followed by a parameter study based on a two-diode-model is presented.

During front contact formation for c-Si cells via Ni-Cu plating on patterned SiN x undesirable ba... more During front contact formation for c-Si cells via Ni-Cu plating on patterned SiN x undesirable background plating can lead to a severe efficiency reduction due to shading, increased recombination and shunting losses. In this work, complete cells based on Ni-Cu metallization are fabricated and background plating is analyzed by surface studies and current-voltage (I-V) based characterization. Reduction in Voc and Jsc by up to 25 mV and 4.23 mA/cm2 along with decreased fill factors obtained from the illuminated I-V data indicate increased recombination losses and reduced shunt resistance. The local ideality factor variation for dark I-V data indicates presence of an additional defect contribution near the maximum power point. Reliable fitting and parameter extraction was possible for such cells by adding a 3rd diode for the resistance limited recombination to the standard two-diode model. This modification facilitates the quantification of efficiency losses due to background plating an...

IEEE Journal of Photovoltaics, 2015

Thin Solid Films, 2008

ABSTRACT Si/SiO2 multiple quantum wells (QWs) are fabricated by remote plasma enhanced chemical v... more ABSTRACT Si/SiO2 multiple quantum wells (QWs) are fabricated by remote plasma enhanced chemical vapor deposition and subsequent rapid thermal annealing. The deposited QWs show strong carrier confinement resulting in effective band gap energies of up to 1.6 eV in 1 nm thick Si wells. The electrical transport characteristics of the QWs are assessed by current voltage measurements in vertical (perpendicular to the Si/SiO2 interfaces) and lateral (parallel to the interfaces) direction. These measurements show a four orders of magnitude increased conductivity in lateral direction compared to QWs with vertical contacts. From lateral photoconductivity measurements mobility lifetime products are derived as a function of QW thickness.

The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO 2 ... more The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO 2 matrix is calculated, including the resonance broadening effects due to distributions of quantum dot diameter and asymmetric barrier thicknesses. The results are in good agreement with experimental data and allow deductions regarding the physical sample structure. The quantum dot size distribution is identified as a major obstacle for the usage of these layers as selective energy contacts in hot carrier solar cells.

ABSTRACT Si/SiO2 multiple quantum wells (QWs) embedded in lateral solar cells are reported. The Q... more ABSTRACT Si/SiO2 multiple quantum wells (QWs) embedded in lateral solar cells are reported. The QWs are fabricated by remote plasma enhanced chemical vapor deposition and are partially recrystallized by subsequent rapid thermal annealing. Extraction of photogenerated charge carriers parallel to the Si/SiO2 interface is investigated. Carrier transport is hampered by the incomplete recrystallization. Open circuit voltage increases with decreasing Si layer thickness, which is caused by a distinct quantum confinement effect within the two-dimensional Si layers. Compared to the conventional QW solar cell concept, where carrier extraction is severely limited by tunneling transport through the insulating SiO2 barrier layers, the fundamental conflict between confinement and transport can be overcome in this new lateral solar cell concept.

ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of... more ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of silicon solar cell using thread parallelism. The device simulated is a rear side passivated cell with rear point contacts (PERC). The optical and electrical behaviour of the device was simulated with Sentaurus Device (formerly dessis). We show that the simulation run-time on a four socket Opteron 6168 machine is reduced down to 24% compared to the run-time on quad-core machine. Furthermore, limits of time reduction by varying the number of threads up to 48 are studied. Thereby, the number of threads for the optimum use of the hardware resources is determined.

ABSTRACT Single-sided solar cell emitters created by phosphorus dopant pastes are an alternative ... more ABSTRACT Single-sided solar cell emitters created by phosphorus dopant pastes are an alternative to the conventional double-sided POCl3 emitters. Thereby, during the emitter formation gettering of impurities such as iron is essential to improve the solar grade wafer quality. In this paper, we demonstrate single-sided screen-printed emitters in monocrystalline Czochralski silicon (Cz-Si) wafers with an improved gettering of iron compared to conventional double-sided POCl3 emitters due to process induced extended gettering time. The phosphorus dopant pastes used had to be chosen carefully to provide a sufficiently suitable emitter sheet resistance and to avoid any iron contamination from the phosphorus dopant paste, which is observed in turn. The iron concentration is determined from the minority carrier lifetime obtained by quasi-steady-state photoconductance measurements, down to very low levels for solar cell material. In addition, the well-known metastable boron-oxygen complexes in Cz-Si have been transferred into a stable state by light-induced degradation prior to these measurements. Therefore, this work shows the correct way how to determine the iron concentration [Fe], when p-type Cz-Si wafers are used.

Energy Procedia, 2010

The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO2 m... more The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO2 matrix is calculated and the resonance broadening effects caused by distributions of quantum dot diameter and asymmetric barrier thicknesses are simulated. It is demonstrated that a size distribution is extremly critical for the use of these structures as selective energy contacts for hot carrier solar cells, requiring precision at the order of 1 Å.

2012 12th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD), 2012

ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of... more ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of silicon solar cell using thread parallelism. The device simulated is a rear side passivated cell with rear point contacts (PERC). The optical and electrical behaviour of the device was simulated with Sentaurus Device (formerly dessis). We show that the simulation run-time on a four socket Opteron 6168 machine is reduced down to 6% compared to the run-time without thread parallelism. Furthermore, limits of time reduction by varying the number of threads up to 48 are studied. Thereby, the number of threads for the optimum use of the hardware resources is determined.

Solar Energy Materials and Solar Cells, 2012

ABSTRACT In this work we report for the first time on the creation of thermal acceptors after las... more ABSTRACT In this work we report for the first time on the creation of thermal acceptors after laser irradiation of a phosphorous doped p-type silicon substrate in ambient atmosphere. The concentration of these defects up to 1020 cm−3 is leading to a conductivity change from n- to p-type just beneath the surface. Electrochemical capacitance voltage (ECV) measurements followed by resistivity measurements confirm this conversion of conductivity. Secondary ion mass spectrometry (SIMS) measurements show significant oxygen incorporation after laser irradiation. The comparison of saturation current density and lock-in thermography measurements of processed wafers in ambient and in nitrogen atmosphere reveal that these defects are electrically active recombination centres that disappear in absence of oxygen. In simulations of the temperature profile during laser processing a correlation between the pulse energy density (EP) and the appearance of thermal acceptors has been observed. The influence of these laser induced acceptor defects on solar cell parameters has been finally investigated. An efficiency loss of 1.3% absolute pertinent to pulse energies usually applied in laser doping process under ambient atmosphere could be avoided by laser processing in nitrogen atmosphere.

A MOS-LED and a p-n LED emitting based on the dislocation-related luminescence (DRL) at 1.5 micro... more A MOS-LED and a p-n LED emitting based on the dislocation-related luminescence (DRL) at 1.5 micron were already demonstrated by the authors. Here we report recent observation of the Stark effect for the DRL in Si. Namely, a red/blueshift of the DRL peak positions was observed in electro-and photo-luminescence when the electric field in the pn-LED was increased/lowered. Fitting the experimental data yields a strong characteristic coefficient of 0.0186 meV/(kV/cm) 2 . This effect may allow realization of a novel Si-based emitter and modulator combined in a single device.

Physica Status Solidi a-Applications and Materials Science, 2011

Comparative structural analyses of a crystallized, 60 nm thick silicon film deposited on quartz s... more Comparative structural analyses of a crystallized, 60 nm thick silicon film deposited on quartz substrate were performed using high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy (RS). Both methods suggest high degree of ...

EPJ Photovoltaics, 2011

We have investigated and proposed a simple method to correlate optical absorption with high B dop... more We have investigated and proposed a simple method to correlate optical absorption with high B doping concentrations in thin SiO2 films that offer a potential doping source for Si quantum dots. SiO2 films with boron and phosphorus were deposited using a computer controlled co-sputtering system. By assessing the absorption coefficients, it was observed that the doping can dramatically increase the absorption of the transparent SiO2. Additionally, the highly doped SiO2 films have a very broad Urbach like absorption tail and the absorption corresponds well with the doping level.

Solar Energy Materials and Solar Cells, 2010

We report on electrical transport and quantum confinement in thermally annealed Si/SiO x multiple... more We report on electrical transport and quantum confinement in thermally annealed Si/SiO x multiple quantum well (QW) stacks. Results are correlated with the morphology of the stacks. High temperature annealing of Si/SiO x stacks leads to precipitation of excess Si from the SiO x layers, which enhances the degree of crystallization and increases the grain sizes in the Si QWs compared to the conventional Si/ SiO 2 system. Moreover, the excess Si forms highly conductive pathways between adjacent Si QWs that are separated by ultrathin silicon oxide barriers. This results in an increase of conductivity by up to 10 orders of magnitude compared to the tunneling dominated transport in Si/SiO 2 stacks. The stacks exhibit a distinct quantum confinement as confirmed by photoluminescence measurements.

Progress in Photovoltaics: Research and Applications, 2012

ABSTRACT An algorithm to calculate the current in the two-diode equivalent circuit of a solar cel... more ABSTRACT An algorithm to calculate the current in the two-diode equivalent circuit of a solar cell is described and characterized in detail. It enables fitting measured current–voltage characteristics with hundreds of voltage points and six fit parameters at practically instantaneous speeds and can handle thousands of voltage points within a few seconds, without simplifications of the two-diode model. This performance enables routine two-diode model parameter extraction at in-line speeds, which may help to enhance cell characterization for module integration. The source code is publicly available. Copyright © 2012 John Wiley & Sons, Ltd.

Solar Energy Materials and Solar Cells, 2016

2011 37th IEEE Photovoltaic Specialists Conference, 2011

ABSTRACT The current-voltage (I-V) characteristics of processed industrial multicrystalline silic... more ABSTRACT The current-voltage (I-V) characteristics of processed industrial multicrystalline silicon (mc-Si) solar cells usually vary within a narrow range (e.g. +/−1 % abs. efficiency). Nevertheless, occasionally cells with very low efficiencies are produced with loss mechanisms such as local shunts or areas with unusually high recombination. In this paper we investigated industrial mc-Si solar cells with exceptionally low efficiencies in detail by dark and illuminated I-V measurements followed by an analysis based on the two-diode-model to determine the dominant electrical loss mechanisms. Subsequently spatially-resolved lock-in thermography (LIT) measurements were used to localise defect positions in these solar cells. These defects were electrically isolated with a laser. The solar cells were characterised again using the same analysis methods. For shunted cells an efficiency gain of up to 2.4 % absolute was obtained and the shunts disappeared. A detailed investigation of I-V data before and after laser isolation followed by a parameter study based on a two-diode-model is presented.

During front contact formation for c-Si cells via Ni-Cu plating on patterned SiN x undesirable ba... more During front contact formation for c-Si cells via Ni-Cu plating on patterned SiN x undesirable background plating can lead to a severe efficiency reduction due to shading, increased recombination and shunting losses. In this work, complete cells based on Ni-Cu metallization are fabricated and background plating is analyzed by surface studies and current-voltage (I-V) based characterization. Reduction in Voc and Jsc by up to 25 mV and 4.23 mA/cm2 along with decreased fill factors obtained from the illuminated I-V data indicate increased recombination losses and reduced shunt resistance. The local ideality factor variation for dark I-V data indicates presence of an additional defect contribution near the maximum power point. Reliable fitting and parameter extraction was possible for such cells by adding a 3rd diode for the resistance limited recombination to the standard two-diode model. This modification facilitates the quantification of efficiency losses due to background plating an...

IEEE Journal of Photovoltaics, 2015

Thin Solid Films, 2008

ABSTRACT Si/SiO2 multiple quantum wells (QWs) are fabricated by remote plasma enhanced chemical v... more ABSTRACT Si/SiO2 multiple quantum wells (QWs) are fabricated by remote plasma enhanced chemical vapor deposition and subsequent rapid thermal annealing. The deposited QWs show strong carrier confinement resulting in effective band gap energies of up to 1.6 eV in 1 nm thick Si wells. The electrical transport characteristics of the QWs are assessed by current voltage measurements in vertical (perpendicular to the Si/SiO2 interfaces) and lateral (parallel to the interfaces) direction. These measurements show a four orders of magnitude increased conductivity in lateral direction compared to QWs with vertical contacts. From lateral photoconductivity measurements mobility lifetime products are derived as a function of QW thickness.

The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO 2 ... more The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO 2 matrix is calculated, including the resonance broadening effects due to distributions of quantum dot diameter and asymmetric barrier thicknesses. The results are in good agreement with experimental data and allow deductions regarding the physical sample structure. The quantum dot size distribution is identified as a major obstacle for the usage of these layers as selective energy contacts in hot carrier solar cells.

ABSTRACT Si/SiO2 multiple quantum wells (QWs) embedded in lateral solar cells are reported. The Q... more ABSTRACT Si/SiO2 multiple quantum wells (QWs) embedded in lateral solar cells are reported. The QWs are fabricated by remote plasma enhanced chemical vapor deposition and are partially recrystallized by subsequent rapid thermal annealing. Extraction of photogenerated charge carriers parallel to the Si/SiO2 interface is investigated. Carrier transport is hampered by the incomplete recrystallization. Open circuit voltage increases with decreasing Si layer thickness, which is caused by a distinct quantum confinement effect within the two-dimensional Si layers. Compared to the conventional QW solar cell concept, where carrier extraction is severely limited by tunneling transport through the insulating SiO2 barrier layers, the fundamental conflict between confinement and transport can be overcome in this new lateral solar cell concept.

ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of... more ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of silicon solar cell using thread parallelism. The device simulated is a rear side passivated cell with rear point contacts (PERC). The optical and electrical behaviour of the device was simulated with Sentaurus Device (formerly dessis). We show that the simulation run-time on a four socket Opteron 6168 machine is reduced down to 24% compared to the run-time on quad-core machine. Furthermore, limits of time reduction by varying the number of threads up to 48 are studied. Thereby, the number of threads for the optimum use of the hardware resources is determined.

ABSTRACT Single-sided solar cell emitters created by phosphorus dopant pastes are an alternative ... more ABSTRACT Single-sided solar cell emitters created by phosphorus dopant pastes are an alternative to the conventional double-sided POCl3 emitters. Thereby, during the emitter formation gettering of impurities such as iron is essential to improve the solar grade wafer quality. In this paper, we demonstrate single-sided screen-printed emitters in monocrystalline Czochralski silicon (Cz-Si) wafers with an improved gettering of iron compared to conventional double-sided POCl3 emitters due to process induced extended gettering time. The phosphorus dopant pastes used had to be chosen carefully to provide a sufficiently suitable emitter sheet resistance and to avoid any iron contamination from the phosphorus dopant paste, which is observed in turn. The iron concentration is determined from the minority carrier lifetime obtained by quasi-steady-state photoconductance measurements, down to very low levels for solar cell material. In addition, the well-known metastable boron-oxygen complexes in Cz-Si have been transferred into a stable state by light-induced degradation prior to these measurements. Therefore, this work shows the correct way how to determine the iron concentration [Fe], when p-type Cz-Si wafers are used.

Energy Procedia, 2010

The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO2 m... more The current through a resonant tunneling diode consisting of Si quantum dots embedded in a SiO2 matrix is calculated and the resonance broadening effects caused by distributions of quantum dot diameter and asymmetric barrier thicknesses are simulated. It is demonstrated that a size distribution is extremly critical for the use of these structures as selective energy contacts for hot carrier solar cells, requiring precision at the order of 1 Å.

2012 12th International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD), 2012

ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of... more ABSTRACT We have investigated the potential to accelerate three-dimensional numeric simulation of silicon solar cell using thread parallelism. The device simulated is a rear side passivated cell with rear point contacts (PERC). The optical and electrical behaviour of the device was simulated with Sentaurus Device (formerly dessis). We show that the simulation run-time on a four socket Opteron 6168 machine is reduced down to 6% compared to the run-time without thread parallelism. Furthermore, limits of time reduction by varying the number of threads up to 48 are studied. Thereby, the number of threads for the optimum use of the hardware resources is determined.

Solar Energy Materials and Solar Cells, 2012

ABSTRACT In this work we report for the first time on the creation of thermal acceptors after las... more ABSTRACT In this work we report for the first time on the creation of thermal acceptors after laser irradiation of a phosphorous doped p-type silicon substrate in ambient atmosphere. The concentration of these defects up to 1020 cm−3 is leading to a conductivity change from n- to p-type just beneath the surface. Electrochemical capacitance voltage (ECV) measurements followed by resistivity measurements confirm this conversion of conductivity. Secondary ion mass spectrometry (SIMS) measurements show significant oxygen incorporation after laser irradiation. The comparison of saturation current density and lock-in thermography measurements of processed wafers in ambient and in nitrogen atmosphere reveal that these defects are electrically active recombination centres that disappear in absence of oxygen. In simulations of the temperature profile during laser processing a correlation between the pulse energy density (EP) and the appearance of thermal acceptors has been observed. The influence of these laser induced acceptor defects on solar cell parameters has been finally investigated. An efficiency loss of 1.3% absolute pertinent to pulse energies usually applied in laser doping process under ambient atmosphere could be avoided by laser processing in nitrogen atmosphere.

A MOS-LED and a p-n LED emitting based on the dislocation-related luminescence (DRL) at 1.5 micro... more A MOS-LED and a p-n LED emitting based on the dislocation-related luminescence (DRL) at 1.5 micron were already demonstrated by the authors. Here we report recent observation of the Stark effect for the DRL in Si. Namely, a red/blueshift of the DRL peak positions was observed in electro-and photo-luminescence when the electric field in the pn-LED was increased/lowered. Fitting the experimental data yields a strong characteristic coefficient of 0.0186 meV/(kV/cm) 2 . This effect may allow realization of a novel Si-based emitter and modulator combined in a single device.

Physica Status Solidi a-Applications and Materials Science, 2011

Comparative structural analyses of a crystallized, 60 nm thick silicon film deposited on quartz s... more Comparative structural analyses of a crystallized, 60 nm thick silicon film deposited on quartz substrate were performed using high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy (RS). Both methods suggest high degree of ...

EPJ Photovoltaics, 2011

We have investigated and proposed a simple method to correlate optical absorption with high B dop... more We have investigated and proposed a simple method to correlate optical absorption with high B doping concentrations in thin SiO2 films that offer a potential doping source for Si quantum dots. SiO2 films with boron and phosphorus were deposited using a computer controlled co-sputtering system. By assessing the absorption coefficients, it was observed that the doping can dramatically increase the absorption of the transparent SiO2. Additionally, the highly doped SiO2 films have a very broad Urbach like absorption tail and the absorption corresponds well with the doping level.

Solar Energy Materials and Solar Cells, 2010

We report on electrical transport and quantum confinement in thermally annealed Si/SiO x multiple... more We report on electrical transport and quantum confinement in thermally annealed Si/SiO x multiple quantum well (QW) stacks. Results are correlated with the morphology of the stacks. High temperature annealing of Si/SiO x stacks leads to precipitation of excess Si from the SiO x layers, which enhances the degree of crystallization and increases the grain sizes in the Si QWs compared to the conventional Si/ SiO 2 system. Moreover, the excess Si forms highly conductive pathways between adjacent Si QWs that are separated by ultrathin silicon oxide barriers. This results in an increase of conductivity by up to 10 orders of magnitude compared to the tunneling dominated transport in Si/SiO 2 stacks. The stacks exhibit a distinct quantum confinement as confirmed by photoluminescence measurements.

Progress in Photovoltaics: Research and Applications, 2012

ABSTRACT An algorithm to calculate the current in the two-diode equivalent circuit of a solar cel... more ABSTRACT An algorithm to calculate the current in the two-diode equivalent circuit of a solar cell is described and characterized in detail. It enables fitting measured current–voltage characteristics with hundreds of voltage points and six fit parameters at practically instantaneous speeds and can handle thousands of voltage points within a few seconds, without simplifications of the two-diode model. This performance enables routine two-diode model parameter extraction at in-line speeds, which may help to enhance cell characterization for module integration. The source code is publicly available. Copyright © 2012 John Wiley & Sons, Ltd.