Applied Physics Express 5 (2012) 029101 DOI: 10.1143/APEX.5.029101
Comment on ‘‘Photovoltaic Action in Polyaniline/n-GaN Schottky Diodes’’ [Appl. Phys. Express 2 (2009) 092201] Chang-Feng You and Yow-Jon Lin Institute of Photonics, National Changhua University of Education, Changhua 500, Taiwan Received February 28, 2011; accepted August 20, 2011; published online January 26, 2012
atsuki et al.1) reported the potential of polyaniline (PANI)/n-GaN Schottky contacts for application in ultraviolet-sensitive solar cells. They found that the obtained open-circuit voltage VOC is less than the theoretical value by 0.06 V, which must be due to the low fill factor of 0.49; this is probably attributed to high series resistance (Rs ¼ 1100 ). However, we found the authors’ interpretation as questionable. The reason of this doubt will be described below. The Schottky domination makes a one-diode model [shown in eq. (1) of ref. 2] applicable in their case. The values of the cell parameters for Sample A (AM1.5 solar simulator, as shown in Table I of ref. 1) were used in eq. (1) of ref. 2 to generate the current density–voltage (J–V ) curve and calculate the shunt resistance (RSH ) at Rs ¼ 1100 . RSH is calculated to be 60 k. Then, the values of the cell parameters for Sample A (AM1.5 solar simulator, as shown in Table I of ref. 1) were used in eq. (1) of ref. 2 to generate the J–V curve (shown in Fig. 1) and calculate VOC at Rs ¼ 500 or 2000 . The value of VOC at Rs ¼ 500 or 2000 is compared with the value of VOC at Rs ¼ 1100 (Sample A) in Fig. 1. It is found that VOC is insensitive to the Rs variation. In addition, the values of the cell parameters for Sample A (AM1.5 solar simulator, as shown in Table I of ref. 1) were used in eq. (1) of ref. 2 to generate the J–V curves (shown in Fig. 2) and calculate VOC in the 60 RSH 100 k range. The value of VOC at RSH ¼ 75 or 100 k is compared with the value of VOC at RSH ¼ 60 k (Sample A) in Fig. 2. It is shown that VOC is significantly affected by RSH and the VOC value increases with increasing RSH . It can be seen that by increasing the RSH value from 60 to 100 k, the VOC value increases from 0.67 to 0.79 V, respectively. These facts point to a change in VOC that is RSH related rather than Rs related. The effect of RSH on VOC of a PANI/n-GaN Schottky diode has been investigated based on the one-diode model. We demonstrated that the RSH variation may lead to the change in VOC extracted from J–V characteristics. However, VOC is insensitive to the Rs variation. This information is helpful for solar cell fabrication.
M
Rs=2000 Ω Rs =1100 Ω Rs= 500 Ω
0.6
RSH= ~60 kΩ
2
J (mA/cm )
0.4
0.2
0.0
-0.2 -0.2
0.0
0.2
0.4
0.6
0.8
Voltage (V) Fig. 1. Plot of the dependence of J–V characteristic on the Rs variation (Rs ¼ 2000, 1100, and 500 ) for Sample A (AM1.5 solar simulator).
0.6
(RSH=100 kΩ) (RSH= 75 kΩ) (RSH= 60 kΩ) Rs= 1100 Ω
2
J (mA/cm )
0.4
0.2
0.0
-0.2
-0.2
0.0
0.2
0.4
0.6
0.8
Voltage (V) Fig. 2. Plot of the dependence of J–V characteristic on the RSH variation (RSH ¼ 100, 75, and 60 k) for Sample A (AM1.5 solar simulator).
1) N. Matsuki, Y. Irokawa, T. Matsui, M. Kondo, and M. Sumiya: Appl. Phys.
Express 2 (2009) 092201.
2) F. Khan, S. N. Singh, and M. Husain: Sol. Energy Mater. Sol. Cells 94
(2010) 1473.
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# 2012 The Japan Society of Applied Physics
