Peter Bermel1
Purdue University1
Space-based photovoltaics are an area in which ultra-light weight and ultra-high reliability are both crucial for effectiveness in long-term space missions such as satellites in geosychronous orbits. Transition metal dichalcogenides (TMDCs) offer a unique combination of flexibility in thickness and absorption properties, all the way down to single layers, and thus are a promising baseline material for designing photovoltaic devices with the requisite performance parameters. Here, we consider an ultra-thin tungsten disulfide (WS<sub>2</sub>) based photovoltaic cell, include plasmonic and dielectric front coating-based light trapping structures, and demonstrate substantial short circuit current enhancement, and even greater power density improvements.<br/><br/>Our photovoltaic model consists of a 200 nm thick WS<sub>2</sub>-based heterojunction solar cell, similar to the HIT (heterojunction with intrinsic thin layer) solar cell structure. A 1-D grating light trapping structure has been implemented using silver as the reflector material, with the grating period and thickness optimized for highest absorption enhancement. An anti-reflection coating layer was added to reduce surface reflection, with the thickness optimized to maximize additional absorption. We have simulated our model under the AM0 space solar spectrum over the temperature range of geostationary satellite orbits (40-70°C).<br/><br/>The baseline photovoltaic model design is estimated to have an efficiency around 16%. The absorption enhancement from light trapping increases the short-circuit current (J<sub>SC</sub>) by 25%, which gave an efficiency around 20%. The additional absorption due to anti-reflection coating increases the J<sub>SC</sub> by a further 15%, leading to an efficiency above 23% - comparable to other single-junction space photovoltaic cells. In addition, TMDCs are very resilient and resistant to high energy particles and radiation in the space environment. They are much more robust and reliable compared to most commonly used semiconductors used in terrestrial PV applications. These results show that our TMDC-based composite material system with plasmonic and dielectric front coating-based light trapping is a strong candidate for space photovoltaic applications.