Karsten Bothe | Leibniz Universität Hannover (original) (raw)

Papers by Karsten Bothe

Research paper thumbnail of PV Module Energy Rating Standard IEC 61853-3 Intercomparison and Best Practice Guidelines for Implementation and Validation

Research paper thumbnail of Contacting of Busbarless Solar Cells for Accurate I-V Measurements

37th European Photovoltaic Solar Energy Conference and Exhibition, Oct 27, 2020

In recent years, solar cell development has undergone a major change in metallization layout. In ... more In recent years, solar cell development has undergone a major change in metallization layout. In their most radical form, busbarless solar cells completely omit the busbar and leave the fingers as solely contacting area. Consequently, characterization and calibration laboratories were forced to develop new contacting units. At the same time, the question of the correct arrangement of current and sense contacts arises. To perform accurate and precise measurements of the current-voltage characteristic of busbarless solar cells, we transfer the well-established concept of busbar-resistance neglecting contacting to the measurement of busbarless cells. The result is a universally valid gridresistance neglecting contacting scheme, which provides the same fill factor as one would get if one had contacted the entire metallized area of the solar cell. We demonstrate that a variety of contacting schemes are able to determine this fill factor if the sensing contact is correctly placed. We provide experimental evidence of consistent results for a contacting with 12 contact bars at ISFH CalTeC and 30 wires at Fraunhofer ISE CalLab, respectively. For the fill factor of 15 silicon solar cells with finger line resistances ranging from 0.6 to 12 /cm we show that the En-values between both calibration laboratories are well below 1, demonstrating a very good agreement within the accompanied measurement uncertainty.

Research paper thumbnail of Solar cell efficiency tables (Version 60)

Progress in Photovoltaics, Jun 6, 2022

Consolidated tables showing an extensive listing of the highest independently confirmed efficienc... more Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2022 are reviewed. An appendix describing temporary electrical contacting of large‐area solar cells approaches and terminology is also included.

Research paper thumbnail of Fast and Slow Stages of Lifetime Degradation by Boron–Oxygen Centers in Crystalline Silicon

Research paper thumbnail of Dynamic ILM – An Approach to Infrared-Camera Based Dynamical Lifetime Imaging

World Conference on Photovoltaic Energy Conversion, Nov 18, 2009

Research paper thumbnail of Optical Modeling of Photovoltaic Modules with Ray Tracing Simulations

John Wiley & Sons, Inc. eBooks, Aug 3, 2018

Research paper thumbnail of Interlaboratory Comparison of the PV Module Energy Rating Standard IEC 61853-3

The IEC 61853 standard series "Photovoltaic (PV) module performance testing and energy ratin... more The IEC 61853 standard series "Photovoltaic (PV) module performance testing and energy rating" aims to provide a standardized measure for PV module performance, namely the Climate Specific Energy Rating (CSER). An algorithm to calculate CSER is specified in part 3 based on laboratory measurements defined in parts 1 and 2 as well as the climate data set given in part 4. To test the comparability and clarity of the algorithm in part 3, we share the same input data, obtained by measuring a standard photovoltaic module, among different research organizations. Each participant then uses their individual implementations of the algorithm to calculate the resulting CSER values. The initial blind comparison reveals differences of 0.133 (14.7%) in CSER between the ten different implementations of the algorithm. Despite the differences in CSER, an analysis of intermediate results revealed differences of less than 1% at each step of the calculation chain among at least three participants. Thereby, we identify the extrapolation of the power table, the handling of the differences in the wavelength bands between measurement and climate data set, and several coding errors as the three biggest sources for the differences. After discussing the results and comparing different approaches, all participants rework their implementations individually and compare the results two more times. In the third intercomparison, the differences are less than 0.029 (3.2%) in CSER. When excluding the remaining three outliers, the largest absolute difference between the other seven participants is 0.0037 (0.38%). Based on our findings we identified four recommendations for improvement of the standard series.

Research paper thumbnail of Accuracy of Simplifications for Spectral Responsivity Measurements of Solar Cells

IEEE Journal of Photovoltaics, Mar 1, 2018

Research paper thumbnail of Dynamic photoluminescence lifetime imaging for the characterisation of silicon wafers

Physica Status Solidi (rrl), Oct 28, 2010

Research paper thumbnail of The effect of oxide precipitates on minority carrier lifetime in <i>n</i>-type silicon

Journal of Applied Physics, Dec 7, 2015

Research paper thumbnail of Solar cell efficiency tables (Version 61)

Progress in Photovoltaics, Nov 21, 2022

Consolidated tables showing an extensive listing of the highest independently confirmed efficienc... more Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since July 2022 are reviewed. Graphs showing progress with each cell technology over the 30‐year history of the tables are also included plus an updated list of designated test centres.

Research paper thumbnail of Multi‐Spectrum Method for the Determination of the Spectral Responsivity and the Short‐Circuit Current of Photovoltaic Devices

Solar RRL, May 18, 2023

Herein, a method for the determination of the spectral responsivity (SR) and the short‐circuit cu... more Herein, a method for the determination of the spectral responsivity (SR) and the short‐circuit current under standard test conditions of photovoltaic devices (e.g., solar cells) is presented. This multi‐spectrum SR method requires a spectrally tunable broadband light source irradiating the photovoltaic device with a large number of different spectra. For each spectrum, the light response of the device and the spectral irradiance in the measuring plane are measured. The spectral irradiances are integrated within predefined wavelength intervals and are incorporated together with the measured light response into an equation system which relates them to the (unknown) SR of the photovoltaic device. By solving the equation system, mathematically using regression algorithms, the SR is determined. Due to the usage of a broadband light source, the device operates at realistic injection conditions during measurements. The mathematical background of the multi‐spectrum SR method is described and its applicability is demonstrated on three world‐photovoltaic‐scale‐type solar cells and one large‐area reference cell. Short‐circuit currents from all SR curves are calculated using the tabulated AM1.5 G spectrum. In comparison to the SR reference data, the short‐circuit currents from the multi‐spectrum SR method deviate by less than 0.68%.

Research paper thumbnail of Design of Large Poly‐Si on Oxide Interdigitated Back Contact (POLO IBC) Silicon Solar Cells with Local Al–p <sup>+</sup> Contacts in the Constraints of Measurement and Module Integration

Solar RRL, Sep 23, 2022

Interdigitated back contact (IBC) silicon solar cells with a passivating n‐type poly‐Si on oxide ... more Interdigitated back contact (IBC) silicon solar cells with a passivating n‐type poly‐Si on oxide emitter and an aluminum‐doped p+ base contact on M2‐sized Ga‐doped p‐type Cz wafers are reported. The Al‐doped base contact forms during the firing of the printed contacts and allows for a lean process flow. The device optimization balances recombination at the base contacts against resistive losses and respects constraints set by the need of interconnecting cells in a module and contacting the cells temporally by a measurement chuck. A special sample holder is designed for measuring the Isc–Voc curve of the IBC cell with a busbar‐less metal grid. The pseudo‐efficiency is 24.7%. All fingers of each polarity are connected with wires and an efficiency of 22.3% is measured. The comparison of simulations and measurements reveals that the cell has 23.4% efficiency without the series resistance losses due to the wires. A huge part of the resistive losses in the cell are the transport losses of the majorities in the base dissipating a power that corresponds to 0.76%abs efficiency and the resistive losses at the Al‐doped base contact (0.29%abs).

Research paper thumbnail of Determination of base doping concentration of silicon solar cells from light IV-curves

Nucleation and Atmospheric Aerosols, 2022

Research paper thumbnail of PV module current gains due to structured backsheets

Energy Procedia, Sep 1, 2017

Research paper thumbnail of Impact of the contacting scheme on <i>I-V</i> measurements of metallization-free silicon heterojunction solar cells

Research paper thumbnail of Fundamental consideration of junction formation strategies for phosphorus-doped emitters with J0e < 10 fA/cm2

Energy Procedia, Sep 1, 2017

Research paper thumbnail of Dynamic Photoluminescence Lifetime Imaging for Injection-dependent Lifetime Measurements

Research paper thumbnail of Reverse Saturation Current Density Imaging of Highly Doped Regions in Silicon Employing Photoluminescence Measurements

IEEE Journal of Photovoltaics, Oct 1, 2012

Research paper thumbnail of Approximating the determination of the spectral responsivity of solar cells

The determination of the spectral responsivity is an essential part of solar cell calibration. Ap... more The determination of the spectral responsivity is an essential part of solar cell calibration. Apart from the complete differential spectral responsivity procedure, which yields the most accurate results, the IEC 60904-8 defines four simplifications. We provide detailed information on the expected variations in the calculated spectral responsivity curves for the different simplifications compared to the complete procedure. For non-linear crystalline silicon front junction solar cells, we show that deviations mainly occur at wavelengths above 700 nm and become largest between 1000 to 1200 nm. Even though we found a maximum deviation in spectral responsivity of 7% for the simplification with lowest requirements in bias irradiance, all other simplifications yield deviations well below 3%. This transforms into a deviation of 0.01% in the spectral mismatch factor for an industrial PERC solar cell when using a typical world photovoltaic scale (WPVS) reference solar cell and a class A two-lamp solar simulator. If you are reliant on the use of a simplification, we recommend using the multicolour approach. Even though the singlecolour approach might yield lower deviations in specific cases, it requires knowledge about the maximum in the spectral responsivity, which is not generally known in advance of the measurement. Accepting a slightly higher deviation, the white bias approach is a recommendable alternative.

Research paper thumbnail of PV Module Energy Rating Standard IEC 61853-3 Intercomparison and Best Practice Guidelines for Implementation and Validation

Research paper thumbnail of Contacting of Busbarless Solar Cells for Accurate I-V Measurements

37th European Photovoltaic Solar Energy Conference and Exhibition, Oct 27, 2020

In recent years, solar cell development has undergone a major change in metallization layout. In ... more In recent years, solar cell development has undergone a major change in metallization layout. In their most radical form, busbarless solar cells completely omit the busbar and leave the fingers as solely contacting area. Consequently, characterization and calibration laboratories were forced to develop new contacting units. At the same time, the question of the correct arrangement of current and sense contacts arises. To perform accurate and precise measurements of the current-voltage characteristic of busbarless solar cells, we transfer the well-established concept of busbar-resistance neglecting contacting to the measurement of busbarless cells. The result is a universally valid gridresistance neglecting contacting scheme, which provides the same fill factor as one would get if one had contacted the entire metallized area of the solar cell. We demonstrate that a variety of contacting schemes are able to determine this fill factor if the sensing contact is correctly placed. We provide experimental evidence of consistent results for a contacting with 12 contact bars at ISFH CalTeC and 30 wires at Fraunhofer ISE CalLab, respectively. For the fill factor of 15 silicon solar cells with finger line resistances ranging from 0.6 to 12 /cm we show that the En-values between both calibration laboratories are well below 1, demonstrating a very good agreement within the accompanied measurement uncertainty.

Research paper thumbnail of Solar cell efficiency tables (Version 60)

Progress in Photovoltaics, Jun 6, 2022

Consolidated tables showing an extensive listing of the highest independently confirmed efficienc... more Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2022 are reviewed. An appendix describing temporary electrical contacting of large‐area solar cells approaches and terminology is also included.

Research paper thumbnail of Fast and Slow Stages of Lifetime Degradation by Boron–Oxygen Centers in Crystalline Silicon

Research paper thumbnail of Dynamic ILM – An Approach to Infrared-Camera Based Dynamical Lifetime Imaging

World Conference on Photovoltaic Energy Conversion, Nov 18, 2009

Research paper thumbnail of Optical Modeling of Photovoltaic Modules with Ray Tracing Simulations

John Wiley & Sons, Inc. eBooks, Aug 3, 2018

Research paper thumbnail of Interlaboratory Comparison of the PV Module Energy Rating Standard IEC 61853-3

The IEC 61853 standard series "Photovoltaic (PV) module performance testing and energy ratin... more The IEC 61853 standard series "Photovoltaic (PV) module performance testing and energy rating" aims to provide a standardized measure for PV module performance, namely the Climate Specific Energy Rating (CSER). An algorithm to calculate CSER is specified in part 3 based on laboratory measurements defined in parts 1 and 2 as well as the climate data set given in part 4. To test the comparability and clarity of the algorithm in part 3, we share the same input data, obtained by measuring a standard photovoltaic module, among different research organizations. Each participant then uses their individual implementations of the algorithm to calculate the resulting CSER values. The initial blind comparison reveals differences of 0.133 (14.7%) in CSER between the ten different implementations of the algorithm. Despite the differences in CSER, an analysis of intermediate results revealed differences of less than 1% at each step of the calculation chain among at least three participants. Thereby, we identify the extrapolation of the power table, the handling of the differences in the wavelength bands between measurement and climate data set, and several coding errors as the three biggest sources for the differences. After discussing the results and comparing different approaches, all participants rework their implementations individually and compare the results two more times. In the third intercomparison, the differences are less than 0.029 (3.2%) in CSER. When excluding the remaining three outliers, the largest absolute difference between the other seven participants is 0.0037 (0.38%). Based on our findings we identified four recommendations for improvement of the standard series.

Research paper thumbnail of Accuracy of Simplifications for Spectral Responsivity Measurements of Solar Cells

IEEE Journal of Photovoltaics, Mar 1, 2018

Research paper thumbnail of Dynamic photoluminescence lifetime imaging for the characterisation of silicon wafers

Physica Status Solidi (rrl), Oct 28, 2010

Research paper thumbnail of The effect of oxide precipitates on minority carrier lifetime in <i>n</i>-type silicon

Journal of Applied Physics, Dec 7, 2015

Research paper thumbnail of Solar cell efficiency tables (Version 61)

Progress in Photovoltaics, Nov 21, 2022

Consolidated tables showing an extensive listing of the highest independently confirmed efficienc... more Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since July 2022 are reviewed. Graphs showing progress with each cell technology over the 30‐year history of the tables are also included plus an updated list of designated test centres.

Research paper thumbnail of Multi‐Spectrum Method for the Determination of the Spectral Responsivity and the Short‐Circuit Current of Photovoltaic Devices

Solar RRL, May 18, 2023

Herein, a method for the determination of the spectral responsivity (SR) and the short‐circuit cu... more Herein, a method for the determination of the spectral responsivity (SR) and the short‐circuit current under standard test conditions of photovoltaic devices (e.g., solar cells) is presented. This multi‐spectrum SR method requires a spectrally tunable broadband light source irradiating the photovoltaic device with a large number of different spectra. For each spectrum, the light response of the device and the spectral irradiance in the measuring plane are measured. The spectral irradiances are integrated within predefined wavelength intervals and are incorporated together with the measured light response into an equation system which relates them to the (unknown) SR of the photovoltaic device. By solving the equation system, mathematically using regression algorithms, the SR is determined. Due to the usage of a broadband light source, the device operates at realistic injection conditions during measurements. The mathematical background of the multi‐spectrum SR method is described and its applicability is demonstrated on three world‐photovoltaic‐scale‐type solar cells and one large‐area reference cell. Short‐circuit currents from all SR curves are calculated using the tabulated AM1.5 G spectrum. In comparison to the SR reference data, the short‐circuit currents from the multi‐spectrum SR method deviate by less than 0.68%.

Research paper thumbnail of Design of Large Poly‐Si on Oxide Interdigitated Back Contact (POLO IBC) Silicon Solar Cells with Local Al–p <sup>+</sup> Contacts in the Constraints of Measurement and Module Integration

Solar RRL, Sep 23, 2022

Interdigitated back contact (IBC) silicon solar cells with a passivating n‐type poly‐Si on oxide ... more Interdigitated back contact (IBC) silicon solar cells with a passivating n‐type poly‐Si on oxide emitter and an aluminum‐doped p+ base contact on M2‐sized Ga‐doped p‐type Cz wafers are reported. The Al‐doped base contact forms during the firing of the printed contacts and allows for a lean process flow. The device optimization balances recombination at the base contacts against resistive losses and respects constraints set by the need of interconnecting cells in a module and contacting the cells temporally by a measurement chuck. A special sample holder is designed for measuring the Isc–Voc curve of the IBC cell with a busbar‐less metal grid. The pseudo‐efficiency is 24.7%. All fingers of each polarity are connected with wires and an efficiency of 22.3% is measured. The comparison of simulations and measurements reveals that the cell has 23.4% efficiency without the series resistance losses due to the wires. A huge part of the resistive losses in the cell are the transport losses of the majorities in the base dissipating a power that corresponds to 0.76%abs efficiency and the resistive losses at the Al‐doped base contact (0.29%abs).

Research paper thumbnail of Determination of base doping concentration of silicon solar cells from light IV-curves

Nucleation and Atmospheric Aerosols, 2022

Research paper thumbnail of PV module current gains due to structured backsheets

Energy Procedia, Sep 1, 2017

Research paper thumbnail of Impact of the contacting scheme on <i>I-V</i> measurements of metallization-free silicon heterojunction solar cells

Research paper thumbnail of Fundamental consideration of junction formation strategies for phosphorus-doped emitters with J0e < 10 fA/cm2

Energy Procedia, Sep 1, 2017

Research paper thumbnail of Dynamic Photoluminescence Lifetime Imaging for Injection-dependent Lifetime Measurements

Research paper thumbnail of Reverse Saturation Current Density Imaging of Highly Doped Regions in Silicon Employing Photoluminescence Measurements

IEEE Journal of Photovoltaics, Oct 1, 2012

Research paper thumbnail of Approximating the determination of the spectral responsivity of solar cells

The determination of the spectral responsivity is an essential part of solar cell calibration. Ap... more The determination of the spectral responsivity is an essential part of solar cell calibration. Apart from the complete differential spectral responsivity procedure, which yields the most accurate results, the IEC 60904-8 defines four simplifications. We provide detailed information on the expected variations in the calculated spectral responsivity curves for the different simplifications compared to the complete procedure. For non-linear crystalline silicon front junction solar cells, we show that deviations mainly occur at wavelengths above 700 nm and become largest between 1000 to 1200 nm. Even though we found a maximum deviation in spectral responsivity of 7% for the simplification with lowest requirements in bias irradiance, all other simplifications yield deviations well below 3%. This transforms into a deviation of 0.01% in the spectral mismatch factor for an industrial PERC solar cell when using a typical world photovoltaic scale (WPVS) reference solar cell and a class A two-lamp solar simulator. If you are reliant on the use of a simplification, we recommend using the multicolour approach. Even though the singlecolour approach might yield lower deviations in specific cases, it requires knowledge about the maximum in the spectral responsivity, which is not generally known in advance of the measurement. Accepting a slightly higher deviation, the white bias approach is a recommendable alternative.