Investigation of the Influence of Deep-Level Defects on the Conversion Efficiency of Sibased Solar Cells
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Investigation of the Influence of Deep-Level Defects on the Conversion Efficiency of Sibased Solar Cells Vladimir G. Litvinov1, Nikolay V. Vishnyakov1, Valery V. Gudzev1, Nikolay B. Rybin1, Dmitry S. Kusakin1, Alexander V. Ermachikhin1, Sergey M. Karabanov1, Sergey P. Vikhrov1, Andrey S. Karabanov 2 and Evgeny V. Slivkin1 1 Ryazan State Radio Engineering University, 59/1 Gagarin Str., Ryazan, 390005, Russian Federation 2 Helios-Resource Ltd., Saransk, Mordovia, 1 Proletarskaya Str., 430001, Russian Federation ABSTRACT The influence of deep level defects (DLs) on the conversion efficiency of multicrystalline Si-based standard solar cells (SCs) is investigated. Multicrystalline p-type Si wafers with 156u156 mm dimensions and 200 Pm thickness were used for SCs preparation. Three types of SCs with conversion efficiency 10%, 16.8% and 20.4% were studied using capacitance voltage characteristics method (C-V) and by current deep level transient spectroscopy (I-DLTS). The correlation between the total concentration of DLs and the values of the SCs conversion efficiency is found. INTRODUCTION Currently actual questions of increasing the conversion efficiency of solar energy into electricity and reasons of the degradation of solar cells (SCs) are continuously studied. It has got great economic importance and it is important for saving the planet's ecology. The conversion efficiency of SCs depends on the structure of the solar module, the type of semiconductor materials and etc. Certain structural defects with deep energy levels or deep traps in the band gap in active semiconductor layer affect on the stability of SCs electrical properties. DLs are responsible for the generation-recombination processes and form the recombination component of direct current through the p-n junction. In SCs recombination current leads to reduction conversion efficiency up to 25% [1]. Well known simple equation that explains the relationship of conversion efficiency K of solar energy into electricity is written as equation 1 [2].
K
FF I L VXX Pin
(1)
Where FF is the fill factor, Pin is the power of the SC radiation, IL is the direct current in the load, VXX is the open circuit voltage. The load current in the case of n+-p-junction consists of diffusion and recombination component [2]. See equation 2. IL
q
Dn n i2S § qV · qn i N t σ υT WS § qV · exp ¨ exp ¨ ¸ ¸ τn NA 2 © kT ¹ © 2kT ¹
(2)
911 Downloaded from https://www.cambridge.org/core. Columbia University Libraries, on 27 Aug 2017 at 17:29:31, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2016.42
Where q is the elementary charge, Dn is the electron diffusivity, Wn is the electron lifetime, S is the area of the n+-p-junction, ni is the intrinsic concentration , NA is the shallow acceptor impurity concentration in the p-type base, V is the bias voltage of SC, k is the Boltzmann constant, T is absolute temperature, Nt is DLs concentration, V is the capture cross section of charge carriers (CCs), is the aver
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