Solar cells and light sensors based on nanoparticle-grafted carbon nanotube films.

Carbon nanotubes show great potential in developing solar cells with enhanced power conversion efficiency, yet the device stability has not been thoroughly studied. Here, we show how the interaction between components in a nanotube-based hybrid solar cell could cause a significant change in output voltage and fill factor, resulting in photoinduced degradation in device performance. We functionalized carbon nanotubes with CdS nanoparticles to make hybrid films and deposited these films onto silicon substrates to construct solar cells with efficiencies up to 1.4%. The I-V characteristics show reversible change in response to light illumination, suggesting potential applications as visible-light sensors. The fill factor and open-circuit voltage gradually decrease under continuous illumination, inversely proportional to the incident light energy within a considerable range up to 60 J. The unique photoresponse is attributed to a charge-transfer process between nanotubes and nanoparticles under excitation and to change in series resistance in the solar cells.