Data on lateral collection length of charge carriers depending on pre-white-light soaking process for metal mesh transparent electrode based Cu(In,Ga)Se2 solar cells

The authors have recently reported silver nanowire based Cu(In,Ga)Se2 solar cells [1,2]. Metal mesh based transparent electrodes other than the silver nanowire can be also employed or have a potential to provide a better performance for the solar cells. To select a suitable electrode for a solar cell among metal meshes, it is required to have data on the lateral collection length of charge carriers in the targeted cell. The method to determine the lateral collection has been reported in our previous publication [3]. Here, we report data on the effect of the light intensity during pre-white-light soaking on the lateral charge collection length for metal mesh transparent electrode based Cu(In,Ga)Se2 solar cells.


a b s t r a c t
The authors have recently reported silver nanowire based Cu(In,Ga)Se 2 solar cells [1,2]. Metal mesh based transparent electrodes other than the silver nanowire can be also employed or have a potential to provide a better performance for the solar cells.
To select a suitable electrode for a solar cell among metal meshes, it is required to have data on the lateral collection length of charge carriers in the targeted cell. The method to determine the lateral collection has been reported in our previous publication [3]. Here, we report data on the effect of the light intensity during prewhite-light soaking on the lateral charge collection length for metal mesh transparent electrode based Cu(In,Ga)Se 2 solar cells.  Table 1 summarize the intensity of pre-white-light soaking and 600 nm-narrow-bandwidth-light, and the photocurrent upon illumination of 600 nm-narrow-bandwidth-light immediately after a corresponding the pre-white-light soaking for four cases A, B, C, and D. The diameter of a disk-shaped Al/Ni top electrode formed on CdS/CIGS/Mo planar stack was 1.75 mm. The reflectance of the light off the front CdS surface was 0.09. Fig. 1 shows the variation of the measured photocurrents with illumination conditions for four cases A, B, C, and D. With increasing the intensity of pre-white-light soaking, the photocurrent upon illumination of 600 nm-narrow-bandwidth-light immediately after a corresponding the pre-white-light soaking increased. Fig. 2 shows the determined lateral collection lengths as a function of the intensity of pre-white-light soaking. The value increased from 15.4 to 23.4 mm with increasing the intensity of pre-white-light soaking from 0.11 to 1.0 sun. The lateral collection length data will be useful to design a suitable network for silver nanowire based CIGS thin film solar cells [1,2].

Data
Specifications Table   Subject Electrical engineering Specific subject area Solar cells Type of data Value of the data The solar light intensity is not fixed but varied during day time. Therefore, it is required to have data regarding the effect of solar light intensity on the lateral collection length of charge carriers to properly design a metal mesh electrode for solar cells.
The data can be useful for device/process engineers who are responsible for determining a type of transparent electrode for a solar cell. Depending on the lateral collection length of chare carriers, it can be determined which one, mesh type or thin film type, is the most suitable for a targeted solar cell. In metal mesh transparent electrode based Cu(In,Ga)Se 2 (CIGS) solar cells, charge carriers are laterally collected along a buffer layer, CdS in this work. Alternative buffer layers without a toxic element have been studied elsewhere, and they will show different values of the lateral collection length from CdS. The lateral collection length will be one of criteria in selecting an alternative buffer layer for metal mesh transparent electrode based CIGS solar cells.

Table 1
The intensity of pre-white-light soaking and 600 nm-narrow-bandwidth-light, and the photocurrent upon illumination of 600 nm-narrow-bandwidth-light immediately after a corresponding the pre-white-light soaking for four cases A, B, C, and D.

Experimental design, materials, and methods
The measured device has a structure of Al/Ni/CdS/CIGS/Mo. Al/Ni is disk-shaped, and formed by ebeam evaporation through a shadow mask on the CdS/CIGS/Mo planar stack. The reflectance of the light off the front CdS surface was measured using an UVeVis spectrometer. Photocurrents were measured from the short-circuited device under light illumination generated by a solar simulator. The intensity of white-light, employed for pre-white-light soaking process, shining the device was controlled by adjusting the device-to-solar simulator distance. The 600 nm-narrow-bandwidth-light, which was employed to determine the lateral collection length of charge carriers, was generated by inserting a 600 nm-band pass filter between the device and the solar simulator. The lateral collection lengths were determined using equation (4) of our previous work [3].