Impact of the p+ layer on current-voltage characteristics of Cu(In,Ga)Se2-based solar cells

Abstract

Cu(In,Ga)Se2-based solar cells often exhibit fill factor losses at low temperature, in particular after red illumination or reverse biasing. A narrow p+ layer between the absorber and buffer layers is commonly assumed to explain these effects. In this contribution, we analyze by means of analytical and numeric models the influence of the parameters of the p+ layer on current-voltage characteristics. Specifically, we find expressions linking the voltage at which the deterioration of the current-voltage curve begins with the acceptor density and the width of the p+ layer. Moreover, we derive formulas describing the height of the barrier in the conduction band caused by the p+ layer. Examples of the analysis of simulated current-voltage characteristics using our approach are presented. Based on the voltage at which the decrease of the current starts, it is possible to estimate the upper and lower limits of the density of the acceptors in the p+ layer. Furthermore, we analyze the relationship between the fill factor and the height of the barrier in the conduction band, which is determined by the density of acceptors in the p+ layer.

Absorber composition: A critical parameter for the effectiveness of heat treatments in chalcopyrite solar cells

“…It is evident that in addition to the p + layer for the photogenerated electrons, there is an additional barrier at the A/B interface due to the CB spike. Similarly, for injected electrons at high forward voltage, that is, above V oc , there are again two active barriers: one due to p + layer as considered in the report by Maciaszek 53 and the other one due to CBO at B/W interface. This combination of two barriers causes the rollover as observed in Figure 8A in our case with much lower doping in the p + layer, than assumed by Maciaszek.…”

“…As a result, we form a p‐p + ‐n device structure, and in the energy band diagram under equilibrium conditions, an additional barrier forms near the surface of the absorber (see Figure 9). The impact of the properties of the p + layer on device JV rollover has been studied in detail by Maciaszek 53 . In this report, for simulations, a carrier concentration of 3 × 10 17 cm −3 was used for the p + layer, which is much higher than the calculated values (2 × 10 16 to 4 × 10 16 cm −3 , Table S2) for the Cu‐rich CuInSe 2 devices discussed here.…”

Air-processable high-efficiency CISSe solar cells from DMF molecular solution and their application to perovskite/CISSe tandems

“…Unfortunately, this etching process was found to induce the formation of surface defect complexes (V Cu -V Se ) being acceptor in nature, forming a highly doped p + layer at the CISe/CdS interface in which interfacial recombination and blocking of carrier transport occurs. 55,[59][60][61] The authors also provided the unique features of the Cu-rich films and device built with them by which we can judge if one's films have Cu-rich nature with V Cu -V Se surface defects existing at film surface: (1) Cu-rich PL signal of the films with distinct DA peaks, (2) V oc vs. temperature data showing activation energy of saturation current (E a ) smaller than E g (interfacial recombination) and (3) existence of transport barrier in temperature dependent IV (IVT) curves primarily as a S-shape in the first quadrant (an injection barrier due to the p + interfacial layer) and secondarily as a kink in the fourth quadrant (an extraction barrier) along with (4) admittance spectroscopy (AS) signal with a defect activation energy ranged from 170 to 200 meV, in which 200 AE 20 meV was detected for unpassivated absorbers (a typical value for V Cu -V Se complex) and 175 AE 5 meV was reported for partially surfacepassivated films with sulfur. 55,62 Keeping these diagnostic features of Cu-rich films in mind, we performed a series of electrical analyses on our devices to answer the fundamental question: Do our CISSe films and devices have the same Cu-rich characteristics suggested by Susanne et al?…”

An Analytical Model for Sb2Se3 Thin‐Film Solar Cells by Considering Current‐Voltage Distortion

“…The V kink can be determined based on the equation J(V kink ) = 0.95 × J(V bias < V kink ). [51,52] In other words, V kink starts where the current is equal to 95% of the value of the smooth section of the curve (= J sc ). For V bias values greater than V kink , the electron barrier formed in the conduction band drastically reduces the current.…”

“…Also, according to the equality of 4), the formula that connects the electric field E(x) and the 𝜑(x) is presented as follows: [52] E(x Sb 2 Se 3 )…”