Abdullah Uzum

Sprayed and Spin-Coated Multilayer Antireflection Coating Films for Nonvacuum Processed Crystalline Silicon Solar Cells

Using the simple and cost-effective methods, spin-coated ZrO2-polymer composite/spray-deposited TiO2-compact multilayer antireflection coating film was introduced. With a single TiO2-compact film on the surface of a crystalline silicon wafer, 5.3% average reflectance (the reflectance average between the wavelengths of 300 nm and 1100 nm) was observed. Reflectance decreased further down to 3.3% after forming spin-coated ZrO2 on the spray-deposited TiO2-compact film. Silicon solar cells were fabricated using CZ-Si p-type wafers in three sets: (1) without antireflection coating (ARC) layer, (2) with TiO2-compact ARC film, and (3) with ZrO2-polymer composite/TiO2-compact multilayer ARC film. Conversion efficiency of the cells improved by a factor of 0.8% (from 15.19% to 15.88%) owing to the multilayer ARC. was improved further by 2 mA cm−2 (from 35.3 mA cm−2 to 37.2 mA cm−2) when compared with a single TiO2-compact ARC.

Water Soluble Aluminum Paste Using Polyvinyl Alcohol for Silicon Solar Cells

Screen-printing aluminum is still dominantly used in the solar cell fabrication process. Ethyl cellulose is one of the main contents of screen-printing pastes that require dichloromethane for its cleaning process, a substance renowned for being extremely toxic and threatening to the human body. Developing environmental friendly aluminum pastes is essential in order to provide an alternative to the commercial pastes. In this work, new, nontoxic polyvinyl alcohol-based aluminum pastes are introduced. Polyvinyl alcohol was used as a soluble polymer that can be synthesized without saponification and that is also soluble in water. Three different pastes were developed using different recipes including many aluminum particle sizes varying from 3.0 to 45 μm, aluminum oxide with particle sizes between 35 and 50 μm, and acetic acid. Evaluation of the pastes was carried out by Scanning Electron Microscope (SEM) image analysis, sheet resistance measurements, and fabricating silicon solar cells using each paste. Solar cells with 15.6% efficiency were fabricated by nonvacuum processing on CZ-Si p-type wafers using developed aluminum pastes on the back side.

Perovskite/crystalline silicon tandem solar cells fabricated by non-vacuum-process

Silicon solar cells and perovskite solar cells were fabricated by non-vacuum printed processes in our group. Screen-printing, spin coating and spray pyrolysis deposition techniques were utilized mainly. Low temperature and non-vacuum processed TiO2 layer and Al2O3 layer and Al2O3/TiO2 double layer were introduced as an alternative anti-reflection coating film. In-house developed polyvinyl alcohol based aluminum pastes were also introduced for solar cell applications. p-type crystalline silicon solar cells were fabricated with over 17% conversion efficiency with non-vacuum processes. On the other hand, perovskite solar cells using organic or inorganic hole-transporting materials can be reach the conversion efficiency over 12%. Finally, a two terminal tandem solar cells with structure of <;perovskite top cell/Au/ (w/ or w/o)Ag nano electrode/crystalline silicon bottom cell> were fabricated using these solar cells and Voc of 1.38 V was achieved.

Silica-sol-based spin-coating barrier layer against phosphorous diffusion for crystalline silicon solar cells

The phosphorus barrier layers at the doping procedure of silicon wafers were fabricated using a spin-coating method with a mixture of silica-sol and tetramethylammonium hydroxide, which can be formed at the rear surface prior to the front phosphorus spin-on-demand (SOD) diffusion and directly annealed simultaneously with the front phosphorus layer. The optimization of coating thickness was obtained by changing the applied spin-coating speed; from 2,000 to 8,000 rpm. The CZ-Si p-type silicon solar cells were fabricated with/without using the rear silica-sol layer after taking the sheet resistance measurements, SIMS analysis, and SEM measurements of the silica-sol material evaluations into consideration. For the fabrication of solar cells, a spin-coating phosphorus source was used to form the n+ emitter and was then diffused at 930°C for 35 min. The out-gas diffusion of phosphorus could be completely prevented by spin-coated silica-sol film placed on the rear side of the wafers coated prior to the diffusion process. A roughly 2% improvement in the conversion efficiency was observed when silica-sol was utilized during the phosphorus diffusion step. These results can suggest that the silica-sol material can be an attractive candidate for low-cost and easily applicable spin-coating barrier for any masking purpose involving phosphorus diffusion.

Effect of Silicon Surface for Perovskite/Silicon Tandem Solar Cells: Flat or Textured?

Perovskite and textured silicon solar cells were integrated into a tandem solar cell through a stacking method. To consider the effective structure of silicon solar cells for perovskite/silicon tandem solar cells, the optic and photovoltaic properties of textured and flat silicon surfaces were compared using mechanical-stacking-tandem of two- and four-terminal structures by perovskite layers on crystal silicon wafers. The reflectance of the texture silicon surface in the range of 750-1050 nm could be reduced more than that of the flat silicon surface (from 2.7 to 0.8%), which resulted in increases in average incident photon to current conversion efficiency values (from 83.0 to 88.0%) and current density (from 13.7 to 14.8 mA/cm2). Using the texture surface of silicon heterojunction (SHJ) solar cells, the significant conversion efficiency of 21.4% was achieved by four-terminal device, which was an increase of 2.4% from that of SHJ solar cells alone.

Perovskite/p-type crystal silicon tandem solar cells

In order to combine perovskite solar cell and crystal silicon solar cell, indium tin oxide as conductive layer is utilized in terms of high transparency. However, distortion of I-V curve was observed by spattering conductive layer on organic hole transport material layer (Spiro-OMeTAD). In order to analyze and find out the reason of the distortion of I-V curve, perovskite solar cell was fabricated with conductive layer deposited by spattering on the hole transport material changing spattering time. It was turned out that distortion of I-V curve was increased with increase of spattering time and different diode factor was observed by measuring dark I-V curve, which attribute to the distortion of I-V curve.