Efficient polymer-nanocrystal quantum-dot photodetectors

We have realized highly efficient photodetectors based on composites of the semiconducting polymer poly[2-methoxy-5-($2^{\prime }$ -ethylhexyloxy)-1,4-phenylenevinylene] and PbSe nanocrystal quantum dots. The external quantum efficiency in these devices is greater than 1 for electric fields $E\sim 7\times {10}^5\mathrm{V}∕\mathrm{cm}$ . The observed photocurrent gain could be attributed to the carrier multiplication in PbSe nanocrystal quantum dots via multiple exciton generation, and the efficient charge conduction through the host polymer material. This photocurrent gain is observed only when the PbSe nanocrystal band gap is at least three times smaller than the optical energy gap of the active polymer material.