| raded bandgap p-i-n diode solar cells are fabricated with a-(Si,Ge):H deposited by triode PECVD. These cells are optimized for low energy photon absorption, and are suitable for the bottom cell of a tandem cell structure. Initially, a series of a-(Si,Ge):H films with a wide range of germanium contents were grown to determine the alloyed material quality. The techniques used to characterize the material include electrical and optical measurements, as well as EDS, TEM and SEM analysis.;Reproducibly high quality films were deposited using low chamber pressures (;A series of constant bandgap devices were also fabricated to determine the hole transport parameters, as well as the Urbach energy. A new computer model for the internal electric fields is used to analyze the device results. The model determines the quantum efficiency from the internal electric field profile and the hole transport parameters.;The hole mobility lifetime product (;The model was also used to guide the design of the optimized graded bandgap devices. A series of devices were then fabricated and tested. The devices with the best results had a multiple graded i-layer with a minimum bandgap energy of about 1.46 eV, and a thickness of about 0.4... |
