Flexible micromorph tandem a-Si/ c-Si solar cells

The deposition of a stack of amorphous a-Si:H and microcrystalline c-Si:H tandem thin film silicon solar cells micromorph requires at least twice the time used for a single junction a-Si:H cell. However, micromorph devices have a higher potential efficiency, thanks to the broader absorption spectrum of c-Si:H material. High efficiencies can only be achieved by mitigating the nanocracks in the c-Si:H cell and the light-induced degradation of the a-Si:H cell. As a result, c-Si:H cell has to grow on a smooth substrate with large periodicity 1 m and the a-Si:H cell on sharp pyramids with smaller feature size 350 nm to strongly scatter the light in the weak absorption spectra of a-Si:H material. The asymmetric intermediate reflector introduced in this work uncouples the growth and light scattering issues of the tandem micromorph solar cells. The stabilized efficiency of the tandem n-i-p/n-i-p micromorph is increased by a relative 15% compared to a cell without AIR and 32% in relative compared to an a-Si:H single junction solar cells. The overall process T 200 °C is kept compatible with low cost plastic substrates. The best stabilized efficiency of a cell deposited on polyethylene-naphthalate plastic substrate is 9.8% after 1000 h of light soaking at Voc, 1 sun, and 50 °C. © 2010 American Institute of Physics. doi:10.1063/1.3275860