Low cost, single crystal-like substrates for practical, high efficiency solar cells

摘要

It is well established that high efficiency (20%) solar cells can be routinely fabricated using single crystal photovoltaic (PV) materials with low defect densities. Polycrystalline materials with small grain sizes and no crystallographic texture typically result in reduced efficiences. This has been ascribed primarily to the presence of grain boundaries and their effect on recombination processes. Furthermore, lack of crystallographic texture can result in a large variation in dopant concentrations which critically control the electronic properties of the material. Hence in order to reproducibly fabricate high efficiency solar cells a method which results in near single crystal material is desirable. Bulk single crystal growth of PV materials is cumbersome, expensive and difficult to scale up. We present here a possible route to achieve this if epitaxial growth of photovoltaic materials on rolling-assisted-biaxially textured-substrates (RABiTS) can be achieved. The RABiTS process uses well-established, industrially scaleable, thermomechanical processing to produce a biaxially textured or single-crystal-like metal substrate with large grains (50-100 (mu)m). This is followed by epitaxial growth of suitable buffer layers to yield chemically and structurally compatible surfaces for epitaxial growth of device materials. Using the RABiTS process it should be possible to economically fabricate single-crystal-like substrates of desired sizes. Epitaxial growth of photovoltaic devices on such substrates presents a possible route to obtaining low-cost, high performance solar cells.