REG1 - Fraunhofer-Institut für Solare Energiesysteme ISE (FhG)

Summary of EMRP Grant Researcher’s activities

The aim of the REG (FhG) work focused on the development and improvement of reference solar cells (WP2). Improvements of temperature, irradiance, and angular dependence measurements were the second focus (WP3). Diverse activities related to these topics have been performed in parallel.

 A questionnaire was created in order to provide an overview of the specific needs of stakeholders. This questionnaire addressed both the use of the reference devices regarding their different conditions related to different measurement procedures as well as the properties the stakeholders wanted to claim for the reference devices. This questionnaire was distributed and the feedback was collected and summarized in a spreadsheet. The data has been evaluated by PTB (REG D1; JRP D2.1.1).

A broad variety of solar cell technologies were investigated regarding their suitability as reference cells. First of all, the spectral properties of different cell types were compared. Solar cells made of different material, technologies, and structuring were investigated. Reflection, spectral response, internal quantum efficiency, and spectrally resolved linearity were evaluated (REG D2; JRP D2.1.2). In the second step, different cell structures were characterized with sunsVoc and low intensity measurements. The results of these measurements were compared with dark-IV parameters fitted with a two diode model. From this analysis, the low light behaviour in addition to  the ISC were estimated.

A set of n-type based reference cells were selected and encapsulated to act as prototypes of new references. Two cells of different types were sent to the PTB for stability testing. Dark-IV curves were measured to explore the potential changes in cell properties during testing.

Simulation of solar cell properties, of potential cell structures, and technological variations were performed.

Spectral response measurements on different thin film devices were performed. Adapted reference cells were designed (REG D3; JRP D2.1.4).

A cell chuck was designed to contact a solar cell up to 6” both thermally and electrically. One of the main requirements was that the thermal stabilisation should be laterally uniform under 1000W/m² illumination (REG D16; JRP D3.3.2, REG D17; JRP D3.3.4).

Solar cell simulation was used to predict the electro-optical performance of reference solar cells. PD1D and Quokka were used for 1D and 2/3D cell structures. These simulations were compared with real cell structures processed at the cleanroom facility of Fraunhofer ISE (REG D24; JRP D3.4.7). The design and manufacture of the mounted 6” reference cells was improved and tested. 6” cells were investigated regarding stability and electro-optical properties.

The facility for irradiance dependence measurement was improved to cover a wider range of irradiances up to 1000W/m² (REG D12; JRP D3.2.1). The facility for angular dependence measurement was improved to stabilise the cell temperature during a set of measurements at different angels. This was attained by using a mounting chuck as described above in addition to bias light which could be rotated with the cell mounting setup.

The design of the WPVS housing was improved and new samples were manufactured. Initial testing of these samples was performed. A set of 4 WPVS cells was collected, including one in the new housing, to support a RR within the project. Data from the newly implemented temperature dependent measurement procedure was analysed (REG D5; JRP D2.2.1).

The improved procedure for the measurement of the temperature coefficients of 6” cells was investigated. The procedure, and its evaluation, is described in REG D18 (JRP D3.3.5). The measurement setup for the angular dependant spectral response measurements was investigated. A detailed uncertainty analysis is described in REG D23 D3.4.6. Solar cell device simulations were applied to different cell structures and compared with opto-electrical measurements (D3.4.7). A newly designed chuck was created and tested with special consideration of its thermal uniformity (D3.3.4). Different types of reference cells were investigated regarding their thermal conduction. 2x2cm² WPVS and different types of mounted 6” solar cells were investigated, optimized, and reported in D2.2.1. A summary is given on the optimisation of the WPVS reference elements (REG D6; JRP D2.2.2).

The improved procedure for the measurement of the temperature coefficients was investigated in more detail and the uncertainty was calculated using the MC method. This is part of the REG D19 (JRP D3.3.6) and D2.3.2.

The samples for the inter-comparison (REG D8; D2.3.1, REG D9; JRP D2.3.2) were selected and prepared (REG D7; JRP D2.2.3). The protocol for the inter-comparison was defined.

Cells for the bonded large area samples (6”) cells were selected. Dark-IV and Electroluminescence measurements were applied for quality control. Several iterations of bonding applied to the samples.

The spectral response setup was optimized regarding the polarisation distribution in order to improve the angular dependent measurement.

Angular dependent measurements were applied to a set of samples (REG D25; JRP D3.4.11).

For linearity testing, the WLR-method (white light response) was used and applied to several samples (REG D13; JRP D3.2.2, REG D14; JRP D3.2.6).

In the last month, the measurements on the newly developed reference cells and the specially prepared industrial cells were done. The uncertainty estimation was improved for the temperature coefficient determination based on a Monte Carlo method (REG D19; D3.3.6). The newly manufactured and improved reference cells were prepared for the inter-comparison and measured with different methods. The angular response (D3.4.11) and the linearity (D3.2.6) were measured with the integral WLR method. Spectral response measurements and IV-curves were performed at different temperatures (WP3).

The data for the measurements was delivered to the PTB for comparison purposes (REG D10; JRP D2.3.3).


The work in WP 2 successfully led to a new generation of WPVS reference cells with higher stability, better thermal conduction, and which are better adapted to the newest cell technologies which are currently commercially available.

The new measurements were used for a cell texturization study published for the IEEE conference and JPV IEEE (DOI: 10.1109/JPHOTOV.2016.2614120)