Quantum well waveguide solar cells and methods of constructing the same

Abstract

A material structure and device design are provided that produce efficient photovoltaic power conversion. Materials of different energy gap are combined in the depletion region of a semiconductor junction. A wider energy gap barrier layer is positioned to reduce the diode dark current by suppressing both carrier injection across the junction and recombination rates within the junction. Light guiding layers are placed above and below the active region of the device in order to enhance optical absorption in the lower energy gap material.

What is claimed is:  
     
         1 . A III-V quantum well thin film solar cell device comprising:
 a III-V semiconductor extended emitter PN heterojunction, in which the extended emitter heterojunction defines an emitter layer of one dopant type overlying a smaller band gap base layer of another dopant type, which further comprises a PN junction depletion region adjacent to the emitter layer that contains material with higher energy gap than the base layer; and   at least one narrow energy gap well inserted into a depletion region of the extended emitter heterojunction structure adjacent to the base layer; and   a top window layer comprised of a III-V semiconductor having a higher energy gap than the emitter layer and top metal contacts; and   a bottom back surface field layer comprising a III-V semiconductor having a higher energy gap than the base layer and a bottom metal contact; and   a top antireflective structure comprising an optical coating of at least one layer, such that the refractive index of the optical coating is intermediate between a refractive index of a top side of the III-V semiconductor thin film solar cell and a refractive index of air.   
     
     
         2 . The III-V quantum well thin film solar cell device of  claim 1  wherein the top antireflective structure comprises an optical coating having at least two layers, one composed of nanorods of material selected from one of indium tin oxide, titanium dioxide, silicon dioxide, and zinc oxide. 
     
     
         3 . The III-V quantum well thin film solar cell device of  claim 1  wherein a transition from a wide band gap material to a narrow band gap material in the depletion region is compositionally graded. 
     
     
         4 . The III-V quantum well thin film solar cell device of  claim 3  further comprising a plurality of narrow energy gap material layers, and wherein the at least one narrow energy gap well comprises a compositionally step graded structure. 
     
     
         5 . The III-V quantum well thin film solar cell device of  claim 4  wherein the emitter comprises n-type InGaP, the base layer comprises p-type GaAs, the wide band gap region of the depletion region adjacent to the emitter comprises undoped AlGaAs, and the at least one narrow energy gap well comprises InGaAs. 
     
     
         6 . The III-V quantum well thin film solar cell device of  claim 4  wherein the emitter comprises p-type AlGaAs, the base layer comprises n-type GaAs, the wide band gap region of the depletion region adjacent to the emitter comprises undoped InGaP and AlGaAs, and the at least one narrow energy gap well comprises InGaAs. 
     
     
         7 . The III-V quantum well thin film solar cell device of  claim 1  further comprising a bottom contact structure that comprises a metal film and a bottom optical coating comprising at least one layer located between the metal film and a back side of the semiconductor thin film solar cell structure. 
     
     
         8 . The III-V quantum well thin film solar cell device of  claim 7  wherein at least one layer in the bottom optical coating comprises a porous transparent conductive oxide film having a nanorod structure, including one of indium tin oxide and aluminum doped zinc oxide. 
     
     
         9 . The III-V quantum well thin film solar cell device of  claim 1  wherein electrical contacts to the top emitter side of the extended heterojunction are formed by etching holes in a backside of the semiconductor thin film solar cell structure. 
     
     
         10 . The photovoltaic device as set forth in  claim 1  further comprising multiple quantum dot layers inserted into the depletion region of the extended emitter heterojunction structure. 
     
     
         11 . A method of manufacturing a photovoltaic device comprising:
 locating a thin film solar cell structure between an overlying, forward-scattering, antireflective top structure and an underlying, back-scattering bottom structure; and   forming a plurality of electrical contacts on a predetermined top region of the thin film solar cell structure and a predetermined bottom region of the thin film solar cell structure.   
     
     
         12 . The method as set forth in  claim 11  wherein the locating is performed by (a) growing an epitaxial structure inverted on a GaAs substrate via metal organic chemical vapor deposition, (b) depositing the back optical coating and metal film, (c) attaching a new supporting substrate, (d) removing the III-V epitaxial layers from the GaAs substrate, and (e) depositing the front optical coating, and the forming is performed by forming metallic contacts and gridlines, and further comprising encapsulating the device. 
     
     
         13 . The method of  12  wherein the porous optical coatings are deposited via oblique-angle deposition. 
     
     
         14 . The method of  claim 11  wherein the thin film solar cell structure is connected to a coated glass substrate. 
     
     
         15 . The method of  claim 11  wherein the thin film solar cell structure is connected to a flexible substrate.