Doped Emitters to Unlock Lowest Cost Solar Electricity

在世界许多地区，太阳能光伏即将取代化石燃料，成为成本最低的电力来源，并有望大幅减少碳排放。基于CdTe的第二代薄膜光伏具有比硅光伏更低的制造成本和更低的碳足迹。该提案将使薄膜CdTe光伏组件的太阳能转换效率达到或超过硅，从而使太阳能光伏发电能够更快、更广泛地采用。该提议为CdTe光伏界广泛认为的前发射极层带来了新的思考，这是实现砷掺杂CdTe和CdSeTe吸收层潜力的限制因素。预计这将实现超过25%的电池效率和超过22%的模块效率。为了实现这一目标，我们组建了一个世界领先的团队来研究一种新的n型发射极层。Swansea-CSER和Loughborough-CREST的团队结合了CdTe吸收层的As掺杂和氧化层的溅射沉积方面的专业知识。世界领先的团队包括项目合作伙伴-科罗拉多州立大学（美国领先的学术团队），First Solar（领先的薄膜光伏制造商）和NSG Pilkington（领先的薄膜光伏镀膜玻璃产品）。实现砷掺杂CdTe的潜力（由斯旺西团队首创）的挑战是将受体掺杂CdTe层与透明发射器层结合起来，其中n型掺杂浓度超过CdTe层的受体掺杂浓度。对于>1x1016 cm-3的受体掺杂，发射极给体掺杂需要>1x1017 cm-3。此外，导带对准必须为电子收集提供一个小的正步长，这将减少非辐射复合。为了达到这一严格的规格，我们将使用组合技术探索各种不同掺杂剂的潜在氧化物及其合金。这将与优化的合金成分和使用MOCVD掺杂的CdSeTe吸收层相匹配。候选掺杂发射体的稳定性将在制造完整薄膜PV器件的早期阶段进行测试，涉及空气暴露和暴露于工艺步骤。广泛的材料和器件特性将用于理解新型掺杂发射器与提高PV电池效率之间的关系。

Solar PV is on the cusp of becoming the lowest cost source of electricity for many regions of the world, displacing fossil fuels, with the prospect of dramatically reducing carbon emissions. The second generation thin film PV based on CdTe has lower manufacturing cost and lower carbon footprint than silicon PV. This proposal will enable the solar energy conversion efficiency of thin film CdTe PV modules to equal or exceed that of silicon and enabling more rapid and wider adoption of solar PV electricity.This proposal brings fresh thinking to the front emitter layer that is widely recognised in the CdTe PV community as being the limiting factor in realising the potential of the arsenic doped CdTe and CdSeTe absorber layers. This is predicted to achieve over 25% cell efficiency and over 22% module efficiency. To achieve this goal we have put together a world leading team to work on a new n-type emitter layer. The teams at Swansea-CSER and Loughborough-CREST have combined expertise on As doping of the CdTe absorber layer along with sputter deposition of oxide layers. The world leading team includes project partners - Colorado State University (leading academic team in the USA), First Solar (leading thin film PV manufacturer) and NSG Pilkington (leading coated glass products for thin film PV). The challenge for realising the potential for arsenic doped CdTe (pioneered by the Swansea team) is to combine the acceptor doped CdTe layer with a transparent emitter layer where the n-type doping concentration exceeds the acceptor doping concentration of the CdTe layer. For an acceptor doping of >1x1016 cm-3, the emitter donor doping needs to be >1x1017 cm-3. In addition the conduction band alignment must give a small positive step for electron collection which will reduce non-radiative recombination. To achieve this exacting specification we will explore a wide range of potential oxides and their alloys with different dopants using combinatorial techniques. This will be matched to the optimised alloy composition and doping of the CdSeTe absorber layer using MOCVD. Stability of candidate doped emitters will be tested from an early stage with regard to air exposure and exposure to process steps in fabricating the complete thin film PV device. Extensive materials and device characterisation will be used to understand the relationship between the novel doped emitters and improved PV cell efficiency.