S. Solntsev

Extraction of amorphous silicon solar cell parameters by inverse modelling

Abstract A novel and unique numerical method of extraction of physical parameters from the measured characteristics was applied for the first time to single junction p-i-n amorphous silicon solar cells to determine several important input parameters used for their modelling. A set of realistic parameters, which describe the solar cells, has been determined from the fits of simulated behaviour to the measured one. The single junction p-i-n solar cells were deposited at the Utrecht University. A set of input parameters that closely describes the solar cells behaviour is an important step for their further optimisation.

Thin-Film Silicon Solar Cells on 1-D Periodic Gratings With Nonconformal Layers: Optical Analysis

Design of 1-D submicrometer periodic gratings aimed at the enhancement of the short-circuit current density in thin-film silicon solar cells is investigated. A rigorous full-wave analysis is carried out to determine the absorption in amorphous (a-Si:H) and microcrystalline (μc-Si:H) silicon solar cells on substrates with gratings featuring different geometrical characteristics. Maximal photocurrent densities Jph are evaluated in both superstrate (p-i-n) and substrate (n-i-p) configurations, taking into account the nonconformal growth of the layers on the gratings. The Jph relative to that of corresponding flat solar cells was found to be 1.34, 1.24, 1.23, and 1.38 times higher for p-i-n a-Si:H, μc-Si:H-based structures, and n-i-p a-Si:H, μc-Si:H based structures, respectively.

Thermal ideality factor of hydrogenated amorphous silicon p-i-n solar cells

The performance of hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells is limited, as they contain a relatively high concentration of defects. The dark current voltage (JV) characteristics at low forward voltages of these devices are dominated by recombination processes. The recombination rate depends on the concentration of active recombination centers and the recombination efficacy of each of these centers. The first factor causes the ideality factor of the devices to be non-integer and to vary with voltage. The temperature dependence of the dark current can be expressed by its activation energy. For microcrystalline silicon solar cells the activation energy varies with voltage with a so-called thermal ideality factor of 2. This value was derived for devices with a spatially uniform defect distribution and reflects the recombination efficacy. Here we present results of a thickness series of a-Si:H p-i-n solar cells. We have matched the experimental curves with computer simulations, and show that the voltage-dependent ideality factor curve can be used to extract information on the cross sections for electron and hole capture. Also, the activation energy is used as a measure for the mobility gap, resulting in a mobility gap for a-Si:H of 1.69?eV. We find a thermal ideality factor close to 2 for all samples. This is explained with a theoretical derivation, followed by a comparison between the internal electric field strength and the spatial variation of the defect density in the intrinsic layer. The thermal ideality factor is shown to be insensitive to the defect distribution and the recombination profile in the device. It is, therefore, an appropriate parameter to characterize a-Si:H p-i-n devices, providing direct insight on the recombination efficacy.

Performance Analysis of Thin-Film Crystalline Silicon-on-Glass Solar Cells

Performance limits of a heterojunction thin-film crystalline silicon on a glass solar cell (SC) in a substrate configuration were analyzed using the computer simulation program “Advanced Semiconductor Analysis” from the Delft University of Technology. The role of light trapping, due to scattering at randomly rough interfaces, on the absorption in the individual layers of the SC was investigated. The effect of the crystalline silicon absorber thickness, quality and passivation on the external parameters of the SC was evaluated. Using light trapping, the efficiency of an SC with 1- and 10-μm-thick c-Si absorber with a minority carrier lifetime of 10 -4 s and a surface recombination velocity of 10 -1m/s can achieve 13.8% and 17.8%, respectively.

Optical Analysis of Thin-Film Silicon Solar Cells on 1-D Periodic Gratings with Non-Conformal Layers

Design of one-dimensional submicron periodic gratings in thin-film silicon solar cells is investigated by rigorous full-wave analysis. Photocurrent densities are evaluated taking into account the non-conformal growth of the layers on the gratings.

3-D modeling of triple junction solar cells on 2-D gratings with optimized intermediate and back reflectors

Superstrate thin-film silicon triple-junction solar cells on 2-D gratings were optimized using opto-electrical modeling. Tuning the thickness of intermediate and back reflectors and the band gap of the middle cell resulted in 17% initial efficiency.