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Title:
 
Punch-Through Effect in CIGS Thin Film Solar Cells
 
Author(s):
 
T. Ott, T. Walter, R. Schäffler, H.-J. Fecht
 
Keywords:
 
Back Contact, CIGS, Thin Film Solar Cell, Punch-through Effect
 
Topic:
 
Thin Film Solar Cells and Modules
Subtopic: CdTe, CIS and Related Thin Film Solar Cells and Modules
Event: 32nd European Photovoltaic Solar Energy Conference and Exhibition
Session: 3AO.6.3
 
Pages:
 
1089 - 1092
ISBN: 3-936338-41-8
Paper DOI: 10.4229/EUPVSEC20162016-3AO.6.3
 
Price:
 
 
0,00 EUR
 
Document(s): paper
 

Abstract/Summary:


Cu(In,Ga)Se2 (CIGS) continuously demonstrates more of its potential with cell efficiencies exceeding 22% on laboratory scale. A goal for the future is the reduction of the absorber thickness. In the past a phototransistor model was introduced to explain the cell behavior for low temperatures or after long term endurance test. This phototransistor model depends on a back contact barrier which becomes more important for a reduced thickness or low doping densities of the absorber. In this contribution the occurrence of a punch-through effect during long term endurance test with an applied negative bias is discussed. In the field negative voltages could occur due to partial shading. From transistor theory the punch-through effect is well known. If the space charge region of the Schottky barrier and the main junction touch, a punch-through occurs resulting in a strong increase of the current and a significantly reduced open circuit voltage. A reduced doping density of the absorber or/and an increased barrier at the back contact enhance this behavior. This assumption is verified with simulations based on the phototransistor model. Finally, the influence on highly efficient cells with reduced absorber thickness is discussed. For thick absorbers this phenomena should play no role under normal operating conditions. But for a reduced absorber thickness the punchthrough effect can occur in the initial state and have a negative influence on the cell performance for cells with thinner absorbers. If the trend towards reduced absorber thicknesses in the future continues, further investigations regarding the back contact barrier including the adjustment of the doping density are necessary.