Effects of Temperature on I-V Characteristics of InAs/GaAs Quantum-Dot Solar Cells Saichon Sriphan1, Suwit Kiravittaya1, Supachok Thainoi2 and Somsak Panyakaew2 1Dapartment of Electrical and Computer Engineering, Faculty of Engineering, Naresuan University, Phitsanulok 65000, Thailand. 2The Semiconductor Device Research Laboratory, Department of Electrical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand.

Contents Introduction QD Solar Cell Structure Experimental Procedure Result and Discussion Conclusion

Introduction Quantum Dot (QD) - Nanostructure (size ~1-100 nm) QD (Material 1) smaller bandgap (CB) Matrix (Material 2) larger bandgap (Eg) CB (VB) QD VB - Nanostructure (size ~1-100 nm) - Three-dimensional electron confinement

(Jagadish et al., SPIE Newsroom 2010) Introduction QDs have band gaps that are tunable. - Novel solar cell structure pointed out to use nanomaterials (e.g., QDs, QWs,…) into structure because of its performance, in particular used QDs into structure. (Jagadish et al., SPIE Newsroom 2010) (http://www.lancaster.ac.uk/gallery/quantum-dots/)

Introduction One of an external factor such as operating temperature, Tcell, can cause defects and reduces efficiency. Isc increase slightly Voc decrease (http://en.wikipedia.org/wiki/Theory_of_solar_cells) Isc = Short circuit current Voc = Open circuit voltage

Introduction Major parameters of solar cell circuit can be varied and causing cell degradation. This work presents and discusses the effects of temperature on QD solar cell. General solar cell equivalent circuit

QD Solar Cell Structure Area mm2 The samples were fabricated by using the MBE and a metal evaporator. This structure is called to the Schottky-barrier-type QD solar cell.

Experimental Procedure Experiment setup Agilent E3633A DC power supply 5.5V 0.5W commercial solar cell 24V 300W overhead projector tungsten lamp Keithley 6485 picoammeter Agilent 34401A digital multimeter Agilent U1186A K-type thermocouple

Experimental Precedure Measurement circuit

Experimental Precedure Experimental steps Shining light In dark condition, the sample is put into a black box. The interested temperature in range of 30oC to 60oC (5oC/step). Observing temperature Apply constant voltage Measuring I-V data in each temperature Keeping data for analysis Automatic controlling by Macro Function in M.Excel

Experimental Precedure Experimental steps - Receiving data are separated for 3 groups: I-V data of QD solar cell. I-V data of QD solar cell when temperature is varied. I-V data of reference cell.

Result and Discussion Solar-cell characteristics proof (0.17, 0.9) MPP = Maximum Power Point

Result and Discussion I-V curve of QD solar cell at various Tcell Voc is decreased from 0.37 V to 0.31 V Isc is decreased from 2.1 mA to 1.8 mA Different from the ref. cell !

Result and Discussion Result Analysis - Using lsqcurvefit in Matlab

Conclusion Outlook The effects of temperature The excessively high series resistance effects Outlook Series resistance reduction methods The effects of temperature on the I-V characteristics of QD solar cell are different from a conventional solar cell. The excessively high series resistance has notorious effects on the I-V characteristics. Reduction of series resistance by properly doping of the growth process or measurement arrangement can improve these devices.

Acknownlegement This work is supported by the Higher Education Research Promotion and National Research University Project of Thailand, Office of the Higher Education Commission (EN264A), Ratchadaphiseksomphot Endowment Fund of Chulalongkorn University (RES560530079-EN), National Nanotechnology Center, Thailand Research Fund DPG5380002) and Naresuan University. We would like to thank Assist. Prof. Dr. Akaraphunt Vongkunghae for the measurement equipment used in this work, Dr. Thomas Dittrich for useful comments and Dr. Ongarj Tangmattajittakul for his technical work on the samples.

Supplementary

QDs solar cell samples come from SDRL lab and the structure is explained in this ref. paper