Higher efficiency tandem solar cells through composite-cell current matching.

We expand in detail on a new approach to current matching in double junction solar cells that increases the theoretical maximum efficiencies attainable for many bandgap pairs. In this approach, either or both cell types are repeated one or more times, which provides for improved current matching and 2-terminal operation for a wide variety of bandgap pairs, opening up the opportunity to utilize materials not previously considered. While a multijunction design in which the bandgap of every cell is fully optimized will have higher efficiency, this approach achieves simplicity and potential cost savings by using only two cell types.

Single-beam lifetime measurements via self-induced optical absorption.

We present self-induced absorption, a pump/probe-like modulation technique that uses a single monochromatic laser acting simultaneously as both a pump and a probe. The technique is applicable to any system where the phenomenon that us being excited simultaneously induces additional absorption in the beam through a secondary process, leading to a non-linear power component in the beam transmission. The technique is demonstrated on a silicon wafer, where the non-linear transmission is due to free-carrier absorption, and provides information about the recombination lifetime of the semiconductor.

Procedure to decouple reflectance and down-shifting effects in luminescent down-shifting enhanced photovoltaics.

The down-shifting (DS) process is a purely optical approach used to improve the short-wavelength response of a solar cell by shifting high-energy photons to the visible range, which can be more efficiently absorbed by the solar cell. In addition to the DS effect, coupling a DS layer to the top surface of a solar cell results in a change in surface reflectance. The two effects are intermixed and therefore, usually reported as a single effect.