TRANSIENT-RESPONSE OF THE PHOTOCURRENT IN A-SI-H LAYERS AND SOLAR-CELLS

The transient photocurrent response measured on a-Si:H layers and sola r cells after step-like switch-on of illumination reveals a variety of structures. By changing experimental parameters, e.g. sample temperat ure, irradiance, preceding dark time interval, under some conditions o nly a current deficiency (retarded approach to steady state photocondu ctivity) is observed. This effect is associated with a relatively slow filling of former empty traps. Other conditions lead to overshoot phe nomena in the transients. Model calculations show that the dangling bo nd (DB) states have to be charged significantly before recombination b y charged DBs becomes dominant. If effective recombination occurs rela tively late compared to the trap filling process, an overshoot over th e steady state value is expected. Generation of additional recombinati on centers by light soaking should therefore influence the overshoot s trength and its transient appearance. This is confirmed by transient m easurements on degraded samples.