Crystalline Silicon Solar Cells: Theory and Practice

Module 1: Theory: Brief review of semiconductor device physics - band structure - carrier concentrations - carrier generation and recombination - effective lifetime and surface recombination velocity - carrier transport - optical absorption and reflection. Practice: (i) measurement of sheet resistance of a silicon wafer - determination of the type of wafer - estimation of the mobility and diffusion coefficient of the majority carriers (ii) measurement of carrier lifetime and surface recombination velocity (iii) measurement of reflectivity of a polished silicon surface. Module 2: Theory: p-n junction diodes - derivation of dark IV characteristics including surface recombination - illuminated IV characteristics - contacts - series resistance in solar cells - shunts in solar cells. Practice: Simulation of dark and illuminated IV characteristics of pn junction diodes using PC1D - analysis of fermi levels, potential, electric field and carrier distributions, generation and recombination rates within the diode - simulation of illuminated characteristics using measured reflectance data - leakage currents - impact of various parameters like carrier lifetime, surface recombination, and semiconductor thickness on carrier distributions, recombination currents and dark and illuminated IV of the diode, impact of the above on solar cell performance parameters (Isc, Voc, FF, efficiency). Module 3: Theory: wet clean and etch processes - Diffusion in silicon - plasma etching - thin film growth and deposition (oxidation, PECVD, ALD, evaporation), screen printing process - laser processes for silicon solar cell fabrication Practice: Texturization of silicon surface using KOH, measurement of reflectance, observation of the surface using optical microscope and assessment of pyramid size and distribution, review of device simulation using the measured reflectance data - Phosphorous diffusion using POCl3, design of diffusion process - experiment, sheet resistance measurements - edge isolation process using plasma etching, characterization of edge isolation - PECVD nitride deposition, ellipsometry to determine thickness, reflectance measurements, lifetime measurements - review of simulation using experimentally measured data - screen printing and firing, measurement of linewidths using optical microscope, measurement of bus bar sheet resistance, contact resistance measurements using TLM techniques as applied on solar cell - review of simulations. Module 4: Theory: Design and analysis of solar cells - minimization of optical losses - minimization of recombination losses - quantum efficiency measurements - loss analysis of solar cells Practice: Design and analysis of solar cells using Al-BSF technology, use experimentally determined parameters from previous section to design cells, PC1D and other software like PV light house can be used - fabrication of solar cells with Al-BSF - measurement of solar cell characteristics - discussion of IEC60904, simulation of spectrum as a function of environmental conditions - analysis of dark and illuminated IV - quantum efficiency measurements - analysis of losses in the solar cell - review of simulations.