Study of silicon solar cell at different intensities of illumination and wavelengths using impedance spectroscopy

doi:10.1016/j.solmat.2009.07.002

Solar Energy Materials and Solar Cells

Volume 93, Issue 10, October 2009, Pages 1881-1884

https://doi.org/10.1016/j.solmat.2009.07.002 Get rights and content

Abstract

The electrical properties of an n⁺–p–p⁺ structure-based single-crystalline silicon solar cell were studied by impedance spectroscopy, I–V and spectral response. The impedance spectrum is measured in dark, under different intensities (14, 43, 57, 71, 86, 100 mW/cm²) of illumination and wavelengths (400–1050 nm) of light. Under dark and at low intensities of illumination (<50 mW/cm²) the impedance spectra show perfect semicircles but at high intensities the semicircles are distorted at low frequencies. It is found that illumination provides an additional virtual R₁C₁ network parallel to the initial bulk R_pC_p network observed under dark conditions. The value of virtual resistance R₁ depends on the illumination wavelength and shows an inverse relationship with the spectral response of the device.

Introduction

Impedance spectroscopy (IS) [1] is a non-destructive technique, which is sensitive to small changes in the system and is generally employed by electrochemists to study characteristics of batteries, electrodes and corrosion-related problems. This technique is widely applied to systems modelled by an equivalent circuit to determine their dynamic (ac) characteristics from which physical parameters of the system can be calculated. Impedance spectroscopy is particularly suitable to study properties of junction, interfaces, contacts, etc., wherein a small ac voltage is imposed across the device and the resulting ac current is measured over a pre-determined frequency range. The impedance spectra (a complex plane plot commonly known as Nyquist Plot) of the device is plotted in terms of real (Z′) and imaginary (Z″) components of the impedance (Z*), the values of which depend on the system parameters such as resistance (R), capacitance (C), angular frequency (ω) and a resistance (R_s) associated with the electrical contacts of the device and may be written as $Z^{*} (ω) = Z^{'} + Z^{″} = R_{s} + \frac{R}{1 + (ω R C)^{2}} - j \frac{ω C R^{2}}{1 + (ω R C)^{2}}$

In the recent past, IS has also been employed to measure the dynamic (ac) characteristics of solar cell [2], [3] and induced junction structures [4]; and wherein cell parameters such as the dynamic resistance, transition capacitance, diode factor, effective minority carrier lifetime (τ_eff), series resistance, etc., were determined. The static (dc) characteristics of solar cells are routinely measured as dark and illuminated current–voltage (I–V) characteristics and spectral response (SR). From I–V curves the cell performance parameters such as open-circuit voltage (V_oc), short-circuit current density (J_sc), curve factor (CF), cell efficiency (η), diode factor and dark current are determined besides shunt and series resistances. The spectral response is a measure of device ability to collect charge carriers generated at different wavelengths of solar spectrum from which internal (Q_int) and external (Q_ext) quantum efficiencies, minority carrier diffusion length (L_b) in the base region, apparent dead layer thickness in the emitter and J_sc can be calculated. The use of IS in conjunction with I–V and SR measurements may provide comprehensive information about the quality of material, device performance, processing quality that may be vital for device characterisation, process development and designing of efficient device structures.

In this paper, we report IS, I–V and SR measurements on silicon solar cells from which static and dynamic device parameters were calculated. We have also tried to correlate IS, I–V and SR data.

Section snippets

Experimental

The experimental set-up for impedance measurement consists of a frequency response analyser (Solartron Model FRA, 1260A) and an electrochemical interface (Solartron Model ECI, 1287). FRA generates excitation signal (< 25 mV peak-to-peak to minimise the distortion) of varying frequency (i.e., 10^–2–10⁶ Hz) that is applied to the device through ECI which acts as a sink and maintains the voltage across the device constant. The FRA measures both in phase and quadrature components and gives real and

Results and discussion

The dynamic equivalent circuit of a solar cell is derived from a static equivalent circuit by replacing the diode with the junction, transition and diffusion capacitances, and its dynamic resistance. The equivalent ac-circuit is shown in Fig. 1, wherein a single RC circuit consisting of a parallel resistor (R_p) and capacitor (C_p) exists and the impedance spectrum is, generally, a semicircle with its origin at (R_s+R_p/2, 0), where R_S is the series resistance of the device and the contribution

Conclusions

The dynamic and static characteristics of an n+–p–p+ structure-based single-crystalline silicon solar cell were measured by impedance spectroscopy (IS), I–V and spectral response (SR). The IS measurements were carried out in dark and at different intensities of illumination (0–100 mW/cm²) and at different wavelengths (400–1050 nm). The IS data were analysed using frequency response analyser software from which various circuit parameters were determined. The values of virtual R₁ and C₁ depend on

Acknowledgements

The authors thank the Director, NPL for the permission to publish this work. One of the authors, SK, acknowledges financial support by the Ministry of New & Renewable Energy, Government of India in the form of research fellowship..

References (12)

G. Friesen et al.
Impedance model for CdTe solar cells exhibiting constant phase element behaviour
Thin Solid Films
(2000)
P.K. Singh et al.
Effect of spatial variation of incident radiation on spectral response of a large area silicon solar cell and the cell parameters determined from it
Solar Energy Material and Solar Cells
(2003)
L. Raniero et al.
Study of nanostructured/amorphous silicon solar cell by impedance spectroscopy technique
Journal of Non-Crystalline Solids
(2006)
J.R. Mac Donald et al.
Impedance Spectroscopy
(1987)
R. Anil Kumar et al.
Facility to measure solar cell AC parameters using an impedance spectroscopy technique
Review of Scientific Instruments
(2001)
S. Kumar et al.
Application of an impedance spectroscopy technique to study silicon solar cells and induced n+–p–p+ junction structures
Journal of Optoelectronics and Advanced Materials
(2007)

There are more references available in the full text version of this article.

Cited by (51)

Revealing capacitive and inductive effects in modern industrial c-Si photovoltaic cells through impedance spectroscopy
2023, Solar Energy Materials and Solar Cells
To achieve a high performance in sub-module power conditioning circuits, it is important that power converters are designed in accordance with the photovoltaic (PV) cell impedance at the input. Taking this one step further, exploiting the impedance of cell strings could even support novel power conditioning approaches in PV modules. In this work, we characterize the impedance of eight single-cell laminates based on different industrial c-Si PV cell architectures. This characterization is carried out by impedance spectroscopy in dark conditions at room temperature, and the capacitive and inductive effects are evaluated through equivalent model fitting. By comparing the results for the different laminates, it is revealed how the cell design affects its impedance. Our experiments show that the PN junction capacitance at maximum power point varies for the different cells between 0.30 and 45.6 $μ$ F/cm². The two main factors contributing to a high PV cell capacitance at maximum power point are (i) a low wafer dopant concentration and (ii) a high maximum power point voltage. In high-efficiency c-Si PV cells that will be fabricated in the coming years, increasing capacitances are expected for operation near the maximum power point. Furthermore, the single-cell laminates exhibit inductances between 63 and 130 nH, and our results indicate that the inductance is mostly affected by the number of busbars and the geometry of the metal contacts.
Impedance spectroscopy analysis to probe the role of interface properties of surface micro-engineered PEDOT:PSS/n-Si solar cells
2023, Organic Electronics
Surface properties of silicon (Si) wafers play a critical role in the quality of polymer/Si interface and hence the photovoltaic (PV) performance of the PEDOT:PSS/n-Si hybrid solar cells (HSCs). In this study, the PEDOT:PSS/n-Si interface is thoroughly investigated for aqueous KOH micro-engineered Si surfaces (including the planar-Si surface as reference) based HSCs via electrochemical impedance spectroscopy (EIS), which has rarely been explored for such devices. Dynamic electrical parameters like, junction capacitance (C_P), recombination resistance (R_P), carrier lifetime (τ), built-in potential (V_bi), depletion region width (W_d) and Schottky barrier height (Φ_b) for the micro-engineered HSCs have been analyzed by EIS and co-related with the junction and PV performances. An optimized micro-engineered Si surface offered damage-free surface for the PEDOT:PSS/n-Si interface and resulted in high efficiency (11.82%) HSCs. A direct enhancement of the R_p by ∼5 fold, improved passivation near the interface (τ ∼234 μs) and thus enhanced charge carrier collection probability for the champion textured cell as compared to planar one has been accounted to the enhanced performances. In addition, formation of an effective inversion layer in the n-Si at the PEDOT:PSS/n-Si interface has been confirmed by high V_bi: 0.691 eV and Φ_b: 0.937 eV in the optimal Si surfaces and hence efficient solar cell. The study may help to understand the PEDOT:PSS/n-Si interface on the micro-engineered Si surfaces and guide to design high efficiency HSCs technology.
Impedance spectroscopy of amorphous/crystalline silicon heterojunction solar cells under dark and illumination
2023, Solar Energy
In this article, the electronic properties of a-Si:H/c-Si heterojunction (SHJ) solar cells are analyzed by performing impedance spectroscopy (IS) characterization in the dark and under controlled illuminations. Various dynamic electrical processes occurring at different time scales, ranging from microseconds to milliseconds, are observed mainly in the operating regime of the device. Several distinct characteristics are observed: a) time constant distribution characteristic of the disordered junction, b) typical bias voltage and illumination intensity dependence of the recombination time constant, and c) an additional time constant indicative of a fast process, which appears only under illumination. The impedance spectra of the SHJ cell are best modelled by including a dispersion element, the constant phase element (CPE), in place of a pure capacitor, in its small signal electrical equivalent circuit (EEC), aside from the pure resistive and capacitive elements arranged in a simple configuration. The CPE behavior is assigned to the complex small signal response originating from the distribution of trap levels in the disordered p+-a-Si:H/n-Si heterojunction. Under illumination, a distinct dynamic process is observed compared to the dark condition in the impedance spectra of the device. The variation of the dispersion parameter, resistances, capacitance, and time constants with external stimuli is discussed. In particular, the variation of the recombination time constant with bias is remarkable under different illumination intensities due to the change in the quasi-fermi levels splitting.
Admittance spectra of silicon photocells: From dark mode to weak illuminate mode
2022, Sensors and Actuators A: Physical
Citation Excerpt :
The reason for this phenomenon is associated with the surface inhomogeneity of the current-collecting busbar and the appearance of parallel currents in the p-n junction region, hereinafter called lateral [23]. The electrodynamic photovoltaic cell structure is significantly rearranged upon transition from the dark mode to the illumination operating mode by external radiation [26–28]. In the quasi-stationary approximation, such rearrangement is associated with the appearance of photocurrent source, which is closed to the element external load.
The results of an experimental analysis of the admittance spectra structure in the frequency range of a harmonic test signal from 1 kHz to 10 MHz are presented. The signal amplitude did not exceed 20 mV, the surface density of the recorded photocurrent was limited to a value of 20 mA/cm². Variants of PVC (Photovoltaic Cells) structural schemes in the dynamic approximation, optimal combinations of localized L, R, C parameters explaining the recorded spectra, dispersion characteristics, and Nyquist diagrams are discussed. A significant contribution of the inductive component in the PVC structural scheme is observed in both dark and weakly illuminated modes. The inductive component is associated with the current flow geometry, primarily with lateral currents. The screening effect in the p-n junction zone was noted at low illumination of the PVC surface; it manifests itself in the loss of the dependence of the admittance spectra on the bias voltage.
Impedance spectroscopy of monocrystalline silicon solar cells for photosensor applications: Highly sensitive device
2020, Physica B: Condensed Matter
In this study, the AC impedance measurements have been used to characterize the monocrystalline silicon solar cell device under dark and illumination conditions. AC impedance measurements in the illuminated conditions are analyzed to identify the electronic behavior through equivalent AC circuit representation in terms of lumped parameters obtained by fitting the measured impedance data. The angle impedance phase increases from negative to positive values with increasing illumination conditions. The real part Z′ of the complex impedance value is typically higher at the dark light in the low-frequency region. It decreases gradually with increasing frequency reaching a plateau demonstrating independence on illumination at high frequencies. Nyquist plots exhibited a semicircle associated with the bulk single-crystalline body, and an additional spike is distinguishable at high frequency. The AC electrical conductivity is changed under dark and illumination conditions. Finally, the studied solar cell shows a highly sensitive light impedance response suggesting its suitability for use in photosensor applications.
Negative capacitance within forward biasing voltage of organic device at higher frequencies
2020, Optik
Citation Excerpt :
For V > 0 V and under very low Pin (<0.02 suns) NC is confirmed. The capacitance approximately vanishes at strong Pin which may be ascribed to the photoinduced positive capacitance due to linear increase in the excess carrier density as indicated by Kumar [12–14]. It is recorded a decay of capacitance within depletion area and then it decreases to negative values within accumulation region.
The fabricated structure based on organic magnesium phthalocyanine material for solar cells is investigated. Such device is fabricated by a facile spin coating route. It is observed that negative values of capacitance (NC) and dielectric constant are exhibited within the forward voltage at adjustable frequencies ranges of 500 KHz-1 MHz. In order to understand the mechanism and the behaviour of such device, the capacitance voltage and conductance voltage characteristics in terms of frequency are studied. Based on impedance spectroscopy measurements, the real and imaginary parts of impedance are frequency dependent. The electrical conductivity in terms of voltage of organic diode is investigated within −2 V, +5 V bias voltage range at 500 kHz and 1 MHz. The average of conductivity about 2μ S/cm is then recorded. Many parameters causes the negative capacitance and dielectric constant.

View all citing articles on Scopus

View full text

Study of silicon solar cell at different intensities of illumination and wavelengths using impedance spectroscopy

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgements

Thin Solid Films

Solar Energy Material and Solar Cells

Journal of Non-Crystalline Solids

Impedance Spectroscopy

Facility to measure solar cell AC parameters using an impedance spectroscopy technique

Review of Scientific Instruments

Application of an impedance spectroscopy technique to study silicon solar cells and induced n+–p–p+ junction structures

Journal of Optoelectronics and Advanced Materials