Temperature‐dependent current–voltage and admittance spectroscopy analysis on cesium‐treated Cu (In_{1 − x},Ga_x)Se₂ solar cell before and after heat‐light soaking and subsequent heat‐soaking treatments

Abstract

Recently, we demonstrated the positive effects of heat-light soaking (HLS) and subsequent heat-soaking (HS) on cesium fluoride (CsF) treated Cu(In 1x, Ga x)Se 2 (CIGS) solar cells. However, the role of defects formation and its influence on the electronic properties have not been analyzed. With this motivation, here, we analyzed the electronic properties of CsF-free and CsF-treated CIGS solar cells before and after HLS and subsequent HS treatments using temperature-dependent current-voltage (J-V-T), admittance and low-temperature capacitance-voltage (C-V) measurements. We noticed that CsF-treated CIGS solar cells form a minority carrier trap level after HLS. The subsequent HS treatment was found to be beneficial to compensate this defect level. The admittance measurement showed a shift of the shallow energy position to a higher value after HLS and subsequent HS treatments, irrespective of Cs incorporation. This is expected to be due to the formation of a secondary diode toward the CIGS/molybdenum contact. The positive and negative effects of HLS and subsequent HS treatments on CsF-treated CIGS solar cell are discussed using low-temperature C-V measurements. By optimizing the HLS and HS processes, CsF-treated CIGS solar cells yielded total efficiencies of over 20%.

Suppressed Interface Defects by GeSe2 Post‐Deposition Treatment Enables High‐Efficiency Kesterite Solar Cells

“…To further explore the carrier recombination path of CZTSSe photovoltaic device, J–V–T measurements were carried out. [ 44–46 ] Figure a,b shows the temperature‐dependent current density–voltage characteristic curves of CZTSSe solar cells without and with GeSe 2 ‐PDT, respectively, under dark condition. The recombination path of photogenerated carriers can be determinated using the following equation: $$\[ \begin{array}{*{20}{c}}{Aln\left( {{J_0}} \right) = Aln\left( {{J_{00}}} \right) - \frac{{{E_a}}}{{kT}}}\end{array} \]$$where A is the ideal factor, J 0 is the reverse saturation current density, J 00 represents the pre‐factor that depends on the recombination path, E a is the carrier recombination activation energy, k is the Boltzmann constant, and T is the absolute temperature.…”

“…To further explore the carrier recombination path of CZTSSe photovoltaic device, J-V-T measurements were carried out. [44][45][46] Figure 7a,b shows the temperature-dependent current densityvoltage characteristic curves of CZTSSe solar cells without and with GeSe 2 -PDT, respectively, under dark condition. The recombination path of photogenerated carriers can be determinated using the following equation:…”

Effect of Se‐Free Annealing on Cesium Fluoride‐Treated Cu(In,Ga)Se2 Thin Films and Corresponding Solar Cells

“…In our previous experiments, we noticed that annealing of CsF‐treated CIGS solar cells forms a back‐contact barrier indicated by J–V rollover. [ 27 ] Hence, it is expected that the CsF 0min‐ann solar cell forms better CIGS/Mo interfaces, leading to larger FF as compared with the CsF 30min‐ann solar cell.…”

“…[ 26,28,29 ] The valence band offset at the buffer/CIGS interface increases with the Alk–In–Se layer, which helps to reduce the interface recombination velocity. [ 26–29 ] The thermodynamic stability of these Alk–In–Se layers increase with increasing alkali radius. [ 29 ] Several strategies to intentionally deposit the alkali‐related secondary layer on the surface of CIGS thin films were reported.…”

“…A heavy alkali‐metal treatment with potassium (K), rubidium (Rb), and cesium (Cs) on the surface of Cu(In,Ga)Se 2 (CIGS) thin films is an effective route to improve solar cell performance. [ 1–31 ] This treatment forms an alkali (Alk = K, Rb, Cs) containing indium–selenium (Alk–In–Se) layer with a larger bandgap on the surface of the CIGS thin film. [ 26,28,29 ] The valence band offset at the buffer/CIGS interface increases with the Alk–In–Se layer, which helps to reduce the interface recombination velocity.…”