The solar cell as a diode

Transcription

1 The solar cell as a diode ENT Keywords Solar energy, photovoltaics, solar cell, diode, and dark characteristic Principle A solar cell consists of a p-doped layer and of an n-doped layer. Under the influence of light, free charge carriers are generated. These charge carriers are pushed outwards by the electric field, thus generating voltage. Due to this layout, the orientation of the voltage is clearly fixed, which enables the following experiment. During this experiment, voltage is applied to the darkened solar cell in order to demonstrate, based on a simple example, that the solar cell has in fact diode characteristics. In an additional partial experiment, the dark curve of the solar cell can be determined. Equipment *2 Connector, straight, module DB *4 Connector, angled, module DB *1 Connector, interrupted, module DB *1 Socket for incandescent lamps, module DB *1 Solar cell, module DB *1 Filament lamp 4 V/0.04 A, 1 out of *1 Cardboards, black, 1 of Adhesive tape **1 Cobra4 Sensor-Unit Energy **1 Holder for hand-held meters **1 measure software for Cobra Connecting cable, 250 mm, blue Connecting cable, 250 mm, yellow Connecting cable, 750 mm, red Connecting cable, 750 mm, blue Additional equipment 1 Demo physics board with a stand Power supply, universal **1 Cobra4 Wireless Manager **1 Cobra4 Wireless-Link PC, USB port, XP, Vista, Win7 1 Adhesive tape * Included in the ENT 1 set ** Included in the Cobra4 extension set Fig. 1: Experiment set-up P PHYWE Systeme GmbH & Co. KG All rights reserved 1

2 ENT The solar cell as a diode 1. Diode (qualitative approach) Set-up - Set the circuit up as shown in Fig. 1 and connect it to the DC voltage output of the power supply unit. Ensure the correct polarity. - The power supply unit is switched off. - Cut or fold the black cardboard and secure it with adhesive tape so that there are six layers of cardboard on top of each other and that the solar cell module can be completely covered. Procedure - Adjust a voltage of 0 V on the power supply unit. - Switch the power supply unit on. - Slowly increase the voltage from 0 V to 4 V. - Check whether the light bulb lights. - Set the voltage back to 0 V. - Interchange the red and blue cables in the circuit (Fig. 2). - Slowly increase the voltage once more from zero up to 4 V. - Check whether the light bulb lights. - Set the voltage back to 0 V. - Switch the power supply unit off. Fig. 2 Fig. 3: Measurement data recording: relationship between current and voltage in the case of a darkened solar cell 2 PHYWE Systeme GmbH & Co. KG All rights reserved P

3 The solar cell as a diode ENT Observation If the positive pole of the power supply unit is connected to the "+" pole of the darkened solar cell, the light bulb lights. In the other case, it does not light. Evaluation The diode is an electrical component that lets current pass in only one direction. Since the solar cell shows the exact same behaviour, it is, in fact, a diode. 2. Dark curve (quantitative approach) Set-up - Set the circuit up as shown in Fig. 4. Ensure the correct polarity. - Ensure that the red cable of the power supply unit is connected to the ma socket of the Cobra4 Sensor-Unit Energy. Procedure - Start the PC and Windows. - Connect the Cobra4 Wireless Manager to the USB port of the PC. - Start the "measure" software package on the PC. - Connect the Cobra4 Wireless-Link to the Cobra4 Sensor-Unit. After it has been switched on, the Sensor-Unit will be automatically detected and an ID number will be assigned to the Cobra4 Wireless-Link. This number will be displayed. The communication between the Cobra4 Wireless Manager and the Cobra4 Wireless-Link is indicated by way of the data LED. Fig. 4: Experiment set-up for the dark curve P PHYWE Systeme GmbH & Co. KG All rights reserved 3

4 ENT The solar cell as a diode - Switch the Cobra4 Wireless-Link with the connected Cobra4 Sensor-Unit on. The Sensor-Unit and the electrical quantities U, I, P, and W are displayed as the measuring channels. - Load the experiment (Experiment > Open experiment > ). - Set the voltage to 0 V on the power supply unit. - Switch the power supply unit on. - Adjust to a voltage of 1 V. - Start the measurement data recording process in "measure". - Set the voltage very slowly back to 0 V. - Interchange the yellow and blue cables of the circuit. - Set the voltage very slowly back to 1 V. - Stop the measurement data recording process. - Set the voltage to 0 V and switch the power supply unit off. - Transfer the measurement values to the "measure" main program. Observation Fig. 5: Measurement evaluation: relationship between current and voltage in the case of a darkened solar cell Evaluation With the aid of the function "Survey" in Fig. 5, it can be seen that it is not until a voltage of approximately 0.5 V is reached that current flows through the darkened solar cell. If the voltage is negative, no current flows. As of 0.5 V, the current increases. As of a voltage of approximately 0.7 V, it forms a straight line. As a result, the solar cell has the characteristic of a diode. Due to the material of the solar cell, the threshold voltage is around 0.5 V. 4 PHYWE Systeme GmbH & Co. KG All rights reserved P

5 The solar cell as a diode ENT Application If several solar cells are connected in series, it must be ensured that none of the solar cells are shaded or even in complete darkness. In this case, the current intensity would be much lower or there would even be no current flow at all. Notes Corresponding student experiments TESS EN 2.6 The solar cell as a diode (P ) 2.9 Dark characteristic of a solar cell (P ) For the execution of the experiment without a PC, the items on the list (page 1) that are marked with (**) must be replaced with the following items: Experiment P Cobra4 Mobile-Link Cobra4 Sensor-Unit Energy Cobra4 Display-Connect, transmitter and receiver set Holder for hand-held meters Large-scale display Experiment P Analog demonstration multimeter ADM P PHYWE Systeme GmbH & Co. KG All rights reserved 5

6 ENT The solar cell as a diode Room for notes 6 PHYWE Systeme GmbH & Co. KG All rights reserved P