Influence of thin metal as a top electrode on the characteristics of P - I - N   a - Si:H solar cells

Hydrogenated amorphous silicon (a-Si:H) p-n junction solar cells have been fabricated which utilize various metals (Cr, Cu, Al, Pd, Ag) as a top electrode. Experimental and theoretical analysis of photovolatic performance in a-Si:H solar cells as a function of resistivity, optical transmittance, and work function of thin metal films are presented. Metal work function changes the effective built-in potential of p-n junction diodes. Furthermore, a lower work function metal forms a good Ohmic contact for substrate –P+-I-N+– electrode cells, and high work function metals improve Voc of substrate -N-I-P cells. Typical Voc values are 760 mV with Cr–, Cu–, and Al–N-I-P–stainless steel (SS), 700 mV with Pd–N-I-P-SS, 600 mV with Pd–P-I-N-SS, and 540 mV with Cr–P-I-N-SS. Jsc is strongly dependent on transmittance and resistivity of the metal films. Fill factor is independent of the choice of a top electrode. An efficient of 2% has been obtained on a 2 cm2 solar cell.