Takashi Suezaki

High-efficiency amorphous silicon solar cells: Impact of deposition rate on metastability

Hydrogenated amorphous silicon (a-Si:H) films, used for light absorbers of p-i-n solar cells, were deposited at various deposition rates (Rd) ranging over two orders of magnitude (Rd ∼ 2 × 10−3–3 × 10−1 nm/s) by using diode and triode plasma-enhanced chemical vapor deposition (PECVD). The impact of varying Rd on the light-soaking stability of the solar cells has been investigated. Although a reduction of Rd mitigates the light-induced degradation in the typical range of Rd (>10−1 nm/s), it remains present even in the very low Rd (<10−2 nm/s), indicating that the metastable effect persists in a-Si:H regardless of Rd. The best performing cell, whose a-Si:H absorber is characterized by low amount of metastable defect and high bandgap, can be obtained at Rd of ∼1–3 × 10−2 nm/s by triode PECVD. By applying such a-Si:H in the improved p-i-n devices, we demonstrate two record independently confirmed stabilized efficiencies of 10.22% for single-junction and 12.69% for a-Si:H/hydrogenated microcrystalline silicon ...

High Efficiency Thin Film Silicon Hybrid Cell and Module with Newly Developed Innovative Interlayer

The paper discusses the development of a new light trapping scheme for a thin film Si based stacked cell and module, where a newly developed innovative interlayer is inserted between amorphous and microcrystalline Si thin film. This new interlayer leads intentional controlling of the refractive index of it. The interlayer with a lower refractive index of 1.7 at 600 nm exhibits both better reflection towards the top amorphous silicon cell and less absorption loss towards the bottom microcrystalline cell. We also proved by numerical simulation that the effect of the interlayer on light trapping towards the top cell is more enhanced with textured substrate. An initial cell efficiency of 15.0% has been achieved in a small area (1cm2) of its cell with this new interlayer. An initial aperture efficiency of 13.4% has been achieved for a 910times455 mm2 Si HYBRID PLUS module fabricated in a single chamber process of p-i-n microcrystalline cell, which was independently confirmed by AIST

High efficiency thin film silicon solar cell and module

An initial efficiency of 14.5% (Jsc=14.4mA/cm/sup 2/, Voc=1.41V, FF=71.9%) has been achieved for a-Si:H/transparent inter-layer/crystalline Si solar cell (total area of 1cm/sup 2/). Both a-Si and crystalline Si films were fabricated by plasma chemical vapor deposition at low temperature. The short circuit current (Jsc) was enhanced by the introduction of transparent interlayer without increasing the thickness of a-Si:H layer. An initial aperture efficiency of 12.3% has been achieved for 910/spl times/455mm/sup 2/ a-Si/crystalline Si thin film integrated solar cell module. Reasonably high deposition rate of 11 A/s for the deposition of crystalline Si for 1/spl times/1m/sup 2/ area has been achieved. By applying a deposition conditions of this high deposition rate, an initial aperture efficiency of 11.2% has been obtained above sized Si stacked solar cell module.

High-efficiency thin-film silicon solar cells realized by integrating stable a-Si:H absorbers into improved device design

We report that thin-film silicon solar cells exhibiting high stabilized efficiencies can be obtained by depositing hydrogenated amorphous silicon (a-Si:H) absorbers using triode-type plasma-enhanced chemical vapor deposition. The improved light-soaking stability and performance of solar cells are also realized by optimizing the device design, such as p and p–i buffer layers. As a result, we attain independently confirmed stabilized efficiencies of 10.1–10.2% for a-Si:H single-junction solar cells (absorber thickness: ti = 220–310 nm) and 12.69% for an a-Si:H (ti = 350 nm)/hydrogenated microcrystalline silicon (µc-Si:H) tandem solar cell fabricated using textured SnO2 and ZnO substrates, respectively. The relative efficiency degradations of these solar cells are ~10 and 3%, respectively, under 1 sun illumination at 50 °C for 1000 h.

GenPro4 Optical Model for Solar Cell Simulation and Its Application to Multijunction Solar Cells

We present a new version of our optical model for solar cell simulation: GenPro4. Its working principles are briefly explained. The model is suitable for quickly and accurately simulating a wide range of wafer-based and thin-film solar cells. Especially adjusting layer thicknesses to match the currents in multijunction devices can be done with a minimum of computational cost. To illustrate this, a triple junction thin-film silicon solar cell is simulated. The simulation results show very good agreement with external quantum efficiency measurements. The application of an MgF2 antireflective coating or an antireflective foil with pyramid texture is considered. Their effects on the implied photocurrents of top, middle, and bottom cells are investigated in detail.

Thin film silicon solar cell and module

We have been developed a new light trapping scheme for thin film Si stacked module (Si HYBRID PLUS module), where a-Si:H/transparent inter-layer/microcrystalline Si thin film integrated large area solar cell module. An initial aperture efficiency of 13.1% has been achieved for 910/spl times/455 mm/sup 2/ Si HYBRID PLUS module, which was independently confirmed by AIST. This is the first time report for independently confirmed efficiency of large area thin film Si module with interlayer. The 19% increase of short circuit current (I/sub sc/) of this module was obtained by the introduction of transparent interlayer, namely internal light trapping. Stabilized efficiency of mini module exhibited the 12%. Outdoor performances of Si HYBRID (a-Si:H/micro-crystalline Si stacked) solar cell module have been investigated over 4 years for two different kind of modules (top and bottom cell limited, respectively). The Hybrid modules limited by the top cell have exhibited the more efficient performance rather than the bottom limited in natural sunlight at noon.

Electrical Properties and Thermal Stability of Cu/6H-SiC Junctions

Copper (Cu)/6H-SiC Schottky rectifiers were analyzed in detail for the first time. The barrier height of the as-deposited Cu contact on the 6H-SiC(0001) Si-face was determined to be 1.26 eV by internal photoemission spectroscopy. To obtain thermally stable electrical properties, the as-deposited Cu contacts were annealed. Cu/6H-SiC Schottky rectifiers had good electrical properties with the ideality factor below 1.1 even after thermal annealing at 500°C. However, the electrical properties of annealed Cu contacts over 500°C were deteriorated, which is caused by the formation of copper silicides at the Cu/6H-SiC interface.

Radiation resistance of super-straight type amorphous silicon germanium alloy solar cells

Performance degradation of super-straight type amorphous silicon germanium alloy (a-SiGe) solar cells due to proton irradiation are investigated using an in-situ current-voltage (I-V) measurement system. The results show that a-Si solar cells have higher radiation resistance than a-SiGe solar cells. Also, the room temperature annealing effects immediately after irradiation are investigated. It is shown that the recovery of the short-circuit current is especially prominent in all the parameters and is more remarkable as the Ge concentration is lower. The variations of dark I-V characteristics are also analyzed. Based on the obtained results, we propose a radiation hardened design of amorphous silicon alloy multi-junction solar cells.

Optical Simulation of Multi-junction Solar Cells

We introduce our optical model for solar cell design. It is especially suitable for optimization of light-trapping schemes in multi-junction devices. We illustrate this for triple junction thin-film silicon and for perovskite/c-Si tandem solar cells.