Progress Toward Realizing an Intermediate Band Solar Cell—Sequential Absorption of Photons in a Quantum Well Solar Cell

In order to realize an intermediate band solar cell, which promises high photovoltaic energy conversion efficiency, achieving higher photocurrent while maintaining the cell voltage is essential. We report on a transient photocurrent due to the sequential absorption of photons in a single quantum well by continuously pumping to stimulate interband transitions (from a valence band to an intermediate band) and showing an intersubband transition (from an intermediate band to a conduction band) with a pulsed infrared laser. We demonstrate the extent to which multiple-photon absorption can be achieved in quantum well devices and propose that a quantum well is a suitable candidate for an intermediate band solar cell. From the combination of this and other sequential absorption results, it is clear that enhancing the short lifetime of a carrier in the intermediate band is the next step toward achieving a working intermediate band solar cell. In light of this, we enhance our previous suggestion, the photon ratchet intermediate band solar cell, as a means of increasing the electron lifetime.