Porponth Sichanugrist

Light trapping in periodically textured amorphous silicon thin film solar cells using realistic interface morphologies.

The influence of realistic interface morphologies on light trapping in amorphous silicon thin-film solar cells with periodic surface textures is studied. Realistic interface morphologies are obtained by a 3D surface coverage algorithm using the substrate morphology and layer thicknesses as input parameters. Finite difference time domain optical simulations are used to determine the absorption in the individual layers of the thin-film solar cell. The influence of realistic interface morphologies on light trapping is determined by using solar cells structures with the same front and back contact morphologies as a reference. Finally the optimal surface textures are derived.

Theoretical analysis of amorphous silicon solar cells: Effects of interface recombination

The carrier continuity equations for both holes and electrons have been solved in amorphous Si (a‐Si) p‐i‐n solar cells, including the diffusion term, hole‐electron recombination term represented by a Shockley–Read model, and the interface recombination effect. Furthermore, the characteristics illuminated through the p and n layers have been calculated and compared. It is shown that when the i layer is intrinsic, the fill factors obtained by illuminating through the p and n layer are almost the same and both are more than 0.6. Furthermore, we found that the fill factor strongly depends on the interface recombination and a fill factor of more than 0.7 can be obtained by using heterojunction such as a‐SiC:H/a‐Si:H to decrease the interface recombination effect.

Amorphous silicon solar cells with graded boron‐doped active layers

The effect of graded boron doping in the actives (i layers) of hydrogenated amorphous silicon p‐i‐n solar cells was investigated. It was found that the cell characteristics strongly depend on the doping profile. A high conversion efficiency of 9.45% was obtained by gradually doping the i layer with boron in order to achieve a linear profile from the p/i to i/n interface. The best fill factor observed was 0.72.

Light-Trapping and Interface Morphologies of Amorphous Silicon Solar Cells on Multiscale Surface Textured Substrates

The short circuit current and quantum efficiency of silicon thin-film solar cells can be increased by using multiscale surface textures consisting of micro- and nanoscale textures. Adding microtextures to the already existing nanosurface textures leads to an increase of the short circuit current from 15.5 mA/cm2 to almost 17 mA/cm2 for thin amorphous silicon solar cells. To gain insights into the light-trapping properties, finite difference time domain simulations were carried out using realistic interface morphologies. The simulations reveal that the gain of the short circuit current is caused by an increased effective thickness of the solar cell and the scattering properties of the microtextured back reflector. The thickness of the solar cells is increased by the growth of the silicon p-i-n diode on the microtextured surface. The influence of the nanoscale and multiscale surface textures on the quantum efficiency and short circuit current will be discussed.

Enhanced photon management in silicon thin film solar cells with different front and back interface texture.

Light trapping and photon management of silicon thin film solar cells can be improved by a separate optimization of the front and back contact textures. A separate optimization of the front and back contact textures is investigated by optical simulations taking realistic device geometries into consideration. The optical simulations are confirmed by experimentally realized 1 μm thick microcrystalline silicon solar cells. The different front and back contact textures lead to an enhancement of the short circuit current by 1.2 mA/cm2 resulting in a total short circuit current of 23.65 mA/cm2 and an energy conversion efficiency of 8.35%.

Junction Properties of nip and pin Amorphous Si Solar Cells Prepared by a Glow Discharge in Pure Silane

The junction properties of various aSi solar cell structures have been studied in some detail. Various structures of aSi solar cells such as pin, nip, pp-n, and nn-p structures were prepared. The nip solar cell gave a conversion efficiency of 6.86% under AMI (100 mW/cm2) insolation through its n-layer. It is demonstrated experimentally and theoretically that the opto-electronic properties of the undoped layers of aSi solar cells were influenced by residual impurities. The nip cell is shown to be of an np-p or np-p structure because of the residual boron during the deposition process, and gives a higher conversion efficiency under illumination through its n-layer than through the p-layer. The current transport mechanism is shown to depend on the electrical properties of the central (normally undoped) region. Doping the central region with boron causes a decrease in the injection current component into p-layer, and hence an increase in the n-value and the open-circuit voltage.

High-Rate Preparation of Amorphous-Silicon Solar Cells with Monosilane

Hydrogenated amorphous silicon (a-Si:H) films produced from monosilane (SiH4) at high deposition rates of 10-30 A/s were studied. The p-i-n solar cells using these films as i-layers were fabricated with emphasis on the effect of light boron-doping during the i-layer deposition and the buffer i-layer at the p/i interface prepared at a lower deposition rate to minimize the interfacial damage from high-energy charged particles. By optimizing this buffer i-layer, a conversion efficiency of 9.1 % under AM1 (100/mW/cm2) illumination was obtained at a deposition rate of 10 A/s. This high efficiency shows that the buffer i-layer at the p/i interface, prepared at a low deposition rate, is significant for the high-rate preparation of high-performance a-Si:H solar cells.

Novel application of MgF2 as a back reflector in a-SiOx:H thin-film solar cells

We present high-quality a-SiOx:H solar cells with a very thin i-layer of 100 nm fabricated at a low temperature of 100 °C. To boost the photocurrent with such a thin absorber, we suggested the application of a low-index MgF2 buffer at the n-type nanocrystalline silicon oxide (n-nc-SiOx:H)/Ag nanotextured interface to suppress the absorption loss at the Ag back contact. The introduction of MgF2 of only a few nanometers (~4 nm) thickness enhanced the reflection at the n-nc-SiOx:H/Ag interface, which resulted in the reinforcement of the short-circuit current by about 7.3% from 9.60 to 10.30 mA/cm2 while almost maintaining Voc and FF. We demonstrated the efficiency improvement of up to 7.66% by MgF2 at the back contact.

Development of Double-Textured ZnO:B Substrates for Improving Microcrystalline Silicon Solar Cell Performance

Zinc oxide (ZnO) films are widely used as front transparent conductive oxide films in thin-film silicon solar cells. Double-textured B-doped zinc oxide (W-textured ZnO:B) substrates, which are formed by reactive ion etching (RIE) and metal-organic chemical vapor deposition, have a high haze ratio over a wide wavelength range. In this study, we have investigated the RIE conditions necessary to modify the surface morphology and the optical properties of a glass substrate. By increasing the pressure during the RIE process, the surface morphology of etched glass was changed from circular to ellipsoidal shapes, and its texture size increased. A newly developed W-textured ZnO:B substrate fabricated using the modified glass exhibited a higher haze ratio than a conventional W-textured ZnO:B substrate and achieved a higher short-circuit current in microcrystalline silicon solar cells without significant deterioration of open-circuit voltage and fill factor.

Development of high-efficiency tandem silicon solar cells on W-textured Zinc oxide-coated soda-lime glass substrates

In this study, we have investigated the effect of refractive index of Soda-lime glass (SLG) substrates on its surface roughness after being etched by Reactive Ion Etching (RIE). It was found that there was a relationship between the refractive index of the glass and etched surface roughness. Higher roughness was obtained on SLG with lower refractive index. Based on this finding, we can easily control the glass etching process and achieve its good repeatability. Furthermore, ZnO films have been deposited on this etched SLG to achieve W-textured TCO substrates. As a result, a-Si:H/μc-Si:H tandem solar cell fabricated on this developed substrate has a high efficiency of 12.40% showing that this new morphology control of glass etching is a promising method for development of high-efficiency thin-film solar cell.