Effects of defects in semiconductors on reproducibility and performance of thin-film photovoltaic solar cells

Abstract

Thin-film solar cells based on GaAs/Al x Ga (1−x) As showing open circuit voltages of (1100-1170) mV and fill factors of (0.80-0.87) have been exposed to external electrical stresses, and current-voltage characteristics were monitored in order to study the effects of defects present in the device structure. It has been found that peculiar kinks, sudden jumps and various deformations occur in current-voltage curves which could be caused when the Fermi level moves position at the device interface. These changes occur when there is a group of defect levels and the Fermi level is forced to move across these levels. The reproducibility and performance of solar cells heavily depend on the properties of these defect structures, and external forces such as electrical stresses, illumination and temperature variations cause changes in the measured current-voltage characteristics. The observed variations during this work together with examples from the literature are presented and discussed in this paper. It is concluded that the control of these defects present in device structures is crucial in developing stable, durable and high-efficiency thin-film solar cells.

Perovskite solar cells: short lifetime and hysteresis behaviour of current–voltage characteristics

“…In references [18] and [19], similar instabilities of GaAs/ AlGaAs graded bandgap, lab-scale devices were reported.…”

“…The aim of this review paper is to share main author's similar experiences with devices based on commercially established inorganic semiconductors like cadmium telluride (CdTe), gallium arsenide and its aluminium alloy (GaAs/ AlGaAs) and copper indium gallium di-selenide (CuInGaSe 2 or CIGS). Authors summarise their experimental results observed and reported in the literature [17][18][19], and explain these variations with the effects of electronic defects. Instead of ionic migration and polarisation affects the behaviour of these I-V characteristics, the phenomenon is described in terms of slow "trapping" and "de-trapping" of charge carriers in defects within the materials and the device structure.…”

“…Variations in I-V curves measured are common in electronic devices fabricated with commercially established inorganic semiconductors like CdTe, GaAs/AlGaAs and CIGS. The full details can be found in several references [17][18][19] and only a brief description is given here for comparison with results observed from PSCs.…”

Perovskite solar cells: a deep analysis using current–voltage and capacitance–voltage techniques

“…In the case of thin film solar cells, material layer thicknesses are in nm region, and therefore seriously affected by defects. This is where strong "Fermi level pinning" takes place as reported in the past [17][18][19]. Hence, when trying to describe these "non-ideal" systems, it is more appropriate to use the Fermi level as the reference energy level.…”

A Study on the Conduction Mechanism and Evaluation of the Comprehensive Efficiency of Photovoltaic Power Generation in China

“…The technical issue of photovoltaic equipment is still a key factor in comprehensive efficiency improvement. The energy efficiency ratio will be comprehensively improved by decreasing the loss of the current transformer, optimizing the transformation efficiency of photovoltaic array and enhancing the overall efficiency of inverter [18,19]. In addition, Chiu and Chang conclude that the condition of photovoltaic equipment, the load situation of photovoltaic power generation system, operation capability and control level are also key factors that influence the comprehensive efficiency of photovoltaic power generation [20,21].…”