AVS 59th Annual International Symposium and Exhibition
    Energy Frontiers Focus Topic Thursday Sessions
       Session EN-ThP

Paper EN-ThP4
The Investigation of the Shunt Resistance using Conductive AFM and EL Measurements in Si Based Thin Film Solar Cells

Thursday, November 1, 2012, 6:00 pm, Room Central Hall

Session: Energy Frontiers Poster Session
Presenter: M.H. Joo, LG Electronics Advanced Research Institute, Republic of Korea
Authors: M.H. Joo, LG Electronics Advanced Research Institute, Republic of Korea
J.M. Lee, LG Electronics Advanced Research Institute, Republic of Korea
K.H. Park, LG Electronics Advanced Research Institute, Republic of Korea
Correspondent: Click to Email
Silicon (Si)-based solar cells are of great interest for photovoltaic applications, such as bulk type, thin film type, and heterojunction type. Recently amorphous silicon based thin film solar cells have attracted much attention from researchers and engineers because of low consumption of raw materials and low temperature deposition. However, the conversion efficiency of these solar cells is still very poor compared to other types of solar cells. An improved understanding on defects in Si based thin film solar cells is required to further enhance cell performance. Due to the short exposure time and high spatial resolution, camera-based techniques, such as photoluminescence (PL), electroluminescence (EL) and dark lock-in thermography (DLIT), have recently emerged as powerful characterization tools for the investigation of different loss mechanisms in solar cells and modules. And he combination of these techniques with high resolution electrical and structural analysis such as conductive atomic force microscopy (c-AFM) and transmission microscopy (TEM) allow for advanced studies on shunt and for determination of recombination current.

In this report, we studied the evolution of the shunt resistance in Si based thin film solar cells. The solar cell (1x1 cm2) structures have a configuration of glass/Al-doped ZnO (AZO)/ a-Si/ a-SiGe/Al. AZO and Al are top and bottom electrodes respectively, deposited with DC magnetron sputter. A-Si and a-SiGe are used for absorption layers prepared by plasma enhanced chemical vapor deposition (PE-CVD). AZO was textured for the light management before the deposition of absorption layers. For defect investigation of solar cells, we measured the samples with both EL and c-AFM. Electroluminescence is driven by injecting a constant current from a power source into the cell. After EL measurements, current distributions in the local area of the cells were evaluated with c-AFM. EL results show the recombination loss of defect area, which is correlated with high leakage current area of c-AFM results. In the result of TEM analysis, low shunt area in the cells evolved from the crack defects in absorption layers. The surface structures of AZO such as high angle textures and pinhole defects make an important role of crack evolution in the absorption layers. When the sample was controlled with low angle AZO texture and no pinhole defects, there was no recombination loss and leakage current in the cells.