The concept of intermediate band solar cells (IBSC) promise a drastic increase in single junction efficiency (theoretically up to over 60% under concentration), exceeding theoretical predictions made by the Shockley-Queisser limit. In this concept, an intermediate band (IB) is formed within the forbidden gap of the host material, acting as an additional energy level where photons with energy less than the host bandgap can be absorbed, significantly reducing the transmission loss of a single junction solar cell. Unfortunately, thermal escape from the quantum dots limit the two-step photon absorption (TSPA) photocurrent collection to low temperatures. In this talk, we report on growth, fabrication, and characterization of type-II InP QD/InGaP IBSC via MOCVD and show high temperature TSPA photocurrent collection compared to conventional InAs and GaSb QD based IBSCs. Time resolved photoluminescence (TRPL), atomic force microscopy (AFM), and excitation-power dependent PL measurements reveal homogeneous formation of type-II InP QDs in an InGaP host matrix with long carrier lifetimes of up to 250 ns. TSPA response using two light sources (monochromatic light and an IR laser) show photocurrent collection at temperatures up to 250 K for the InP QD cells compared to less than 120 K for InAs and GaSb QD cells. These results clearly establish InP QD/InGaP as a viable material system for IBSC applications.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon