Outcome/Output: | 1. Under this project, two activities are silicon and CIGS based thin film solar cells. Team worked on optimization of process condition for deposition of amorphous & microcrystalline silicon and CIGS thin films for fabrication of solar cells using our existing facilities. Under first activity, efforts were made to refurbish a non functional old multi-zone PECVD system (M/s GSI, USA) in order to grow doped (n- & p- type) and intrinsic amorphous and microcrystalline silicon films in separate chambers on 4 inch x 4 inch substrate. In addition, team deposited amorphous & microcrystalline silicon films using our existing single chamber VHF PECVD system. Few amorphous/microcrystalline silicon based p-i-n solar cells were also fabricated using p-i-n layers deposited in refurbished multi chamber PECVD system.
2. Under second activity, CIGS & CZTS films were deposited using chemical route and CZTS using PLD & sputtering processes. Process optimization for depositing device quality CIGS & CZTS layers for solar cell fabrication is in progress.
3. So far we have procured following equipments: (i) Stylus based thickness profilometer (ii) Components for fabrication of steady state photocarrier grating (SSPG) measurement setup and (iii) High resolution Z contrast Transmission Electron Microscope.
4. Work carried out related to amorphous & microcrystalline silicon solar cells: Mixed phased structure of amorphous and microcrystalline silicon films were deposited using 60 MHz assisted PECVD process at high rate (above 10 A0/sec). More insight understanding was developed in photo-degradation study of micro-crystalline silicon films deposited at high rate using 60 MHz VHF PECVD process. Photodegradation study of these films was performed. Films were quite stable compared to amorphous silicon. It was observed that a typical ?c-Si: H films deposited under certain set of chosen process conditions were of good quality having photo-sensitivity (>103) and photo induced degradation (<5%). It was also observed that microcrystalline films having high crystallinity showed lower photo degradation. It was found that these films were quite stable compared to amorphous silicon. It is observed that after light soaking there is an increase in lattice distortion in these films.
5. Work carried out related to CIGS using chemical route: CIGSe & CZTS films were synthesized by colloidal route and their characterization for process optimization for synthesizing device quality material for solar cell was also carried out. Without resorting topo-selenization treatments at high temperatures, Serich CIGSe based films have been obtained by rapid colloidal synthesis route. Usage of successive purification steps lead to effective removal of insulating barrier of TOP/TOPO capping ligands from the surface of CIGSe nanocrystals which eventually results in effective charge transport. A water free rapid synthesis of organically-capped Se-rich CIGS & related nanocrystals by colloidal route developed. A room temperature processed green chemical route was used for successful removal of organic capping ligands for effective charge transport in CIGS and related nanocrystals.
6. Work carried out related to development of PVD Processes (PLD & magnetron sputtering) for CIGS & CZTS growth: A composite target made of Cu2ZnSn (CZT) has been utilized to deposit composite thin films of CZT by pulsed laser deposition (PLD) technique. Deposited CZT thin films were found to consist of Cu:Zn:Sn in atomic ratio of 38:51:11. The compositions of CZT thin films were not found to be much dependent on process parameters such as Ar pressure (1.0 × 10-3 to 6.0 × 10-2 mbar), substrate temperature (23-150 0C) and aerial energy density (5-2 J/cm2) of laser beam during deposition. Analysis revealed smooth surface morphology of the as-deposited CZT thin films along with the presence of splashed micrometer sized particles. To convert CZT films into CZTS films, CZT films deposited under different conditions were sulfuried at 550 0C for an hour while using elemental sulfur powder as a source to convert CZT to CZTS films, problem of oxidation was observed.
CZTS films along with Mo, ZnO, Al:ZnO thin film have been deposited by sputtering method. The parameters are being optimized. Solar cell with very low efficiency has been made. The parameters are being optimized to achieve the consistency in efficiency. |