Sapna Mudgal | Indian Institute of Technology Delhi (original) (raw)

Papers by Sapna Mudgal

Optics letters/Optics index, Mar 18, 2024

2018 IEEE 7th World Conference on Photovoltaic Energy Conversion (WCPEC) (A Joint Conference of 45th IEEE PVSC, 28th PVSEC & 34th EU PVSEC), 2018

The heterojunction silicon solar cells displaying two different open circuit voltages and having ... more The heterojunction silicon solar cells displaying two different open circuit voltages and having S-shape light current density-voltage characteristics are analyzed by observing change in quantum efficiency (QE) with voltage and light bias conditions. With forward bias voltage close to (and beyond) the S-shape region, the QE is reduced uniformly in all the regions, due to dominance of barrier over junction field for collection of holes. Under white light bias along with the voltage biasing close to the S-shape characteristics, an improvement of QE is observed due to saturation of defects at the interface and enhancement of photoconductivity of the amorphous Si layers. The cell with small open circuit voltage showed considerable improvement in QE from interfacial region (e.g. in the short and long wavelength region), while response in the bulk region (intermediate wavelength region) remains flat.

15th International Conference on Concentrator Photovoltaic Systems (CPV-15), 2019

Carrier-selective contact based silicon heterojunction solar cell of Ag/ITO/MoOx/n-Si/LiFx/Al is ... more Carrier-selective contact based silicon heterojunction solar cell of Ag/ITO/MoOx/n-Si/LiFx/Al is fabricated at room-temperature, having a power conversion efficiency of >15% without using any silicon surface passivation layer. For device fabrication; molybdenum oxide (MoOx) and lithium fluoride (LiFx) are used as hole-and electron-selective thin layers on low-cost industrially feasible Cz n-type silicon wafers, respectively. The device characteristics are investigated by dark/light current density-voltage, quantum efficiency, and capacitance-voltage measurements, and also MoOx/n-Si interface states density by admittance spectroscopy. The performance of cell is found to be limited by the detrimental interface defect states at the MoOx/n-Si interface (~2×10 12 eV-1 cm-2), and also high n-Si/LiFx back-surface recombination that is reflected in quantum efficiency response in the longer wavelength region (800 nm to 1100 nm). Small built-in-potential of ~0.69 V at the MoOx/n-Si interface is observed from the Mott-Schottky plot, which is led to the open-circuit voltage of device to ~0.57 V. The absence of strong inversion layer is due to the presence of large number of interface defect states at the MoOx/n-Si junction, and reverse saturation current density of ~4.1 ×10-8 A/cm 2. EXPERIMENTAL DETAILS The CSC solar cell used in this study was fabricated using as cut (100) oriented n-type Czochralski (Cz) crystalline silicon wafers having doping concentration of ~3×10 15 cm-3 , resistivity of 2-3 Ω-cm, thickness of ~170

IEEE Journal of Photovoltaics, 2018

We have analyzed a-Si:H(p)/a-Si:H(i)/c-Si(n) heterojunction silicon solar cell having the S-shape... more We have analyzed a-Si:H(p)/a-Si:H(i)/c-Si(n) heterojunction silicon solar cell having the S-shaped current densityvoltage characteristics with a low fill factor and open-circuit voltage, using quantum efficiency (QE) characterization technique under forward/reverse voltage and different light (blue, infrared, and white) bias conditions. The curvature of S-shape is sensitive to excitation light intensities because of modification in junction barrier potential (variation in quasi-Fermi levels splitting). With forward-bias voltage alone near/above S-shaped region, cell's QE is uniformly reduced because of reduction in junction field and dominance of barrier for collection of holes. However, with blue and white light at bias voltages close to S-shaped characteristics, a uniform improvement of QE in broad wavelength region is observed because of defects saturation at the junction interface and photoconductivity in the a-Si layers. With white light and voltage bias, cell's QE is anomalously improved and it has even crossed the QE response at no voltage/light bias conditions in the blue region because of defects saturation in a-Si:H layers, whereas under infrared light and voltage bias conditions defect saturation is not displayed in the QE because of carrier generation in a deeper region of the cell after crossing unabsorbed photons front region.

physica status solidi (a), 2019

For the broad use of solar photovoltaic devices, the device fabricated at commercially viable sil... more For the broad use of solar photovoltaic devices, the device fabricated at commercially viable silicon wafers at room temperature is more preferable to harvest abundant solar energy. Silicon heterojunction solar cells at room temperature, based on carrier‐selective layers without using any specified surface passivation layer on the silicon wafer is fabricated. Industrially feasible Cz n‐type non‐textured silicon wafers having the bulk lifetime of 300 µs are used for cell fabrication. The molybdenum oxide (MoOx) and lithium fluoride (LiFx) are used as hole‐ and electron‐selective layers, respectively. The highest conversion efficiency of >15% from the simple architecture of Ag/TCO/MoOx/n‐Si/LiFx/Al is achieved. The internal quantum efficiency of ≈96% is observed in the shorter wavelength region, whereas to understand relatively less response between 800 and 1100 nm wavelength region; effective minority carrier diffusion lengths are estimated. The authors also confirm the inversion ...

Solar Energy, 2019

Role of textured crystalline silicon pyramids size and chemical polishing (CP) for isotropic etch... more Role of textured crystalline silicon pyramids size and chemical polishing (CP) for isotropic etching of pyramid peaks/valleys are investigated from carrier-selective contact silicon heterojunction solar cell performance. With an increase of average pyramids size from 2 to 8 µm, the effective minority carrier lifetimes (τ eff) are reduced from ∼126 to ∼65 µs with molybdenum oxide (MoO x) surface passivation layers. After the CP treatment, an increase in the τ eff is observed for the same respective textures (from ∼154 to ∼99 µs) due to reduction of charge carrier recombination. The solar cell structure of Ag/ITO/MoO x /n-Si/LiF x /Al is fabricated at room temperature. With small pyramids (∼2 µm), the cell has shown the better power conversion efficiency of ∼14.53%, but, after the CP treatment not much efficiency variation is observed. Whereas; the CP treatment is beneficial for medium/large pyramids (∼5-8 µm) based cells, which has enhanced the open-circuit voltage (45-63 mV) after smoothing/rounding of sharp peak/valley surfaces. But, we have observed a reduction in photocurrent due to an increase of light reflection from smoothened pyramid surfaces. Quantum efficiency analysis has provided the better insight with the silicon surface morphology dependent energy conversion. The cells' reverse saturation currents also have analyzed to understand the silicon surface passivation and MoO x /n-Si junction quality. The performance variation of cells is explained by considering low-barrier shunts at the pyramids' peaks/valleys, which influence the junction built-in potential at the depletion region.

Organic Electronics, 2018

Poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) doped with Eu 3+ is spray d... more Poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) doped with Eu 3+ is spray deposited for creating an Anode buffer layer (ABL). The doping of Eu 3+ in PEDOT:PSS causes the down-shifting of the UV light to visible spectrum enhancing the photon concentration in this region. The use of electric field during the spray deposition of undoped and Eu 3+ doped PEDOT:PSS film improved the surface morphology and the electrical conductivity, which help to improve the solar cell performance. The organic solar cell (ITO/ABL/PTB7:PC 71 BM/Al) fabricated using the electric field assisted spray deposited Eu 3+ doped PEDOT:PSS ABL is shown improvement in the power conversion efficiency in comparison to the device fabricated using undoped PEDOT:PSS without electric field. This enhancement in the efficiency of the device in terms of current density and Fill factor can be attributed to an increase in the photon concentration in visible region due to the downshifting and improvement in the surface morphology and conductivity due to applied electric field during deposition.

Solar RRL, 2019

Carrier‐selective contact‐based silicon heterojunction solar cells are fabricated using nickel ox... more Carrier‐selective contact‐based silicon heterojunction solar cells are fabricated using nickel oxide (NiOx) as a hole‐selective layer by thermal evaporation. The highest power conversion efficiency of ≈15.20% with a chemically grown SiOx interlayer is achieved from a Ag/ITO/NiOx/n‐Si/LiFx/Al cell structure in comparison with ≈12.43% without SiOx. The cells without and with the SiOx layer are analyzed by considering crucial parameters for conversion efficiency, such as minority carriers' diffusion lengths, lifetimes, recombination resistance, and density of interface defect states at the NiOx/n‐Si junction, by studying the dark/light current density–voltage, quantum efficiency, impedance, and parallel conductance characteristics. Device analysis provides evidence for the cell's open‐circuit voltage and short‐circuit current enhancement with the SiOx interlayer. This is due to an improvement in minority carrier lifetimes from ≈8.6 to ≈48.27 μs (photo‐conductance decay analysis...

physica status solidi (a), 2020

Solid State Communications, 2021

We have investigated the carrier transport mechanisms of Ag/ITO/NixO/n-Si/LiFx/Al carrier-selecti... more We have investigated the carrier transport mechanisms of Ag/ITO/NixO/n-Si/LiFx/Al carrier-selective contact (CSC) silicon solar cells without and with chemically grown SiOx passivation interlayer. The carrier transport is dominated by thermionic (Schottky) emission and tunnelling at the high- (>0.4 V) and low-forward ( 0.4 V forward voltage bias region. The C–V analysis is also confirmed the inability to hold the excess photo-generated charge carriers because of poor interface quality of the cell without SiOx than the cell with SiOx. The NixO/c-Si junction with the SiOx is resulted in higher built-in voltage and better open-circuit voltage representing better interface passivation quality with fewer interface/surface defect states.

15th International Conference on Concentrator Photovoltaic Systems (CPV-15)

We have investigated charge carrier recombination and transport mechanism in heterojunction silic... more We have investigated charge carrier recombination and transport mechanism in heterojunction silicon solar cells of different configurations like; Ag/ITO/a-Si:H(p+)/a-Si:H(i)/c-Si(n)/a-Si:H(n+)/ITO/Ag (SHJ cell) and Ag/ITO/MoOx/c-Si(n)/LiFx/Al (MoOx cell). Two cells having S-shape in light current density-voltage (J-V) characteristics are analyzed by the Suns-VOC, and quantum efficiency with voltage-and light-bias measurements. The MoOx cell has shown turnaround in the Suns-VOC graph, whereas a linear behaviour has been observed from the SHJ cell. Quantum efficiency analysis has revealed poor performance of the MoOx cell from the backside , for this cell the minority carrier diffusion lengths also is estimated. The S-shape in light J-V graph of MoOx cell is due to carrier extraction barrier for trap assisted tunneling at the MoOx/c-Si interface by the insufficient number of traps, which also is reflected as turnaround in the Suns-Voc characteristics. Whereas; the S-shape in J-V graph of SHJ cell is due to minority charge carrier barrier from the band-offset at a-Si/c-Si junction instead of the Schottky contact barrier, since no turnaround in the Suns-Voc graph.