![]() ![]() ![]() The exceptions to this are metals with very high work functions which form Schottky contacts with small barriers and can thus act effectively as Ohmic-like contacts at normal working temperatures (eg, gold and palladium). (C) Generic idealized semiconductor back contact with small hole barrier and electron reflection character (B) Generic semiconductor back contact with large hole energy barrier. Generalized valence band alignment diagrams for the back contact to CdTe solar cells. The majority of CdTe PV research and all module manufacturing to date has exploited the superstrate configuration. Secondly, a chlorine heat treatment of the CdTe and thirdly, an Ohmic (back) contact to the CdTe. Firstly, a substrate, electrode (front contact), and n-type buffer which are optimized to transmit photons with an energy above the absorber bandgap. The CdTe in superstrate configuration relies on the following factors, among others, to achieve high conversion efficiency. The latter is the preferred route for several optimal device performance reasons and necessitates the use of an optically transparent superstrate material and initial electrode layer. 5, 6ĬdTe PV can be constructed under two device architectures (Figure 1) the PV thin films can be deposited onto a substrate material in the general order electrode, p-type CdTe absorber, n-type buffer layer, electrode or the reverse order transparent substrate material, transparent electrode, n-type buffer, p-type CdTe absorber, and electrode. 2, 4, 5 First Solar are the leading commercial manufacturers of thin film photovoltaics having recently introduced their Series 6 offering in excess of 17% efficiency at the module level. 2, 3 A virtual plateau in efficiency followed for the next 20 years before the efforts of First Solar and GE Global Research (now one entity) helped push the efficiency to 22.1% at the time of this review by the First Solar company. 1 However, progress was slow in reaching this protentional with best laboratory cell efficiencies climbing from ~9% in 1976 to 16% in 1993. CdTe was long recognized for its potential to surpass the conversion efficiencies of conventional silicon solar cells based on bandgap matching to the Shockley Queisser limit. Photovoltaics (PV) using thin film CdTe as a photon absorber have been studied for several decades. Attention is drawn to parallels with back contact materials used on other thin film photovoltaics such as perovskites and kesterites. The authors attempt to identify the more promising material groups. It includes a categorization of back contact interface materials into groups such as oxides, chalcogenides, pnictides, halides, and organics. This review includes both recent and older literature to give a comprehensive picture. ![]() There have been numerous publications on CdTe back contacts since 2014. Excellent reviews of back contacts were published by McCandless and Sites (2011) and Kumar and Rao (2014). The CdTe research community has employed many back contact materials and processes to realize them. Back contact material choice is also influenced by their applicability in more complex architectures such as bifacial and tandem solar cells, where high visible and/or near-infrared transparency is required in conjunction with their electrical properties. Back contact optimization is likely to play a key role in any improvement. The best CdTe devices have short-circuit current close to the limit but open-circuit voltage has much room for improvement. However, there is much potential for progress toward the Shockley-Queisser limit (32%). CdTe is the leading commercial thin film photovoltaic technology with current record laboratory efficiency (22.1%). ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |