Optimized process for the manufacturing of integrated microchannel cooling devices in the back contact of concentrator solar cells

The record efficiencies of the most modern photovoltaic cells currently reach above 45%, which are achieved by concentrator systems (CPV). However, despite better device efficiencies, CPVs have a major drawback: the high amount of waste heat caused by the high power density and the photovoltaic conversion losses. Extracting the heat is an important issue, as the efficiency of the device is significantly reduced if its operational temperature rises. Therefore, especially at higher concentrations, the usage of active cooling methods is unavoidable. Efficient cooling requires the conduction of large quantities of internally generated heat with the achievable minimal thermal resistance. Thus, these applications need new cooling solutions, like microscale integrated cooling devices. This paper presents an effective solution for cooling a 20 x 20 mm concentrator photovoltaic cell. In our concept, the microscale channels are integrated into the back surface metallization, formed by electroplating copper around a photoresist channel pattern. This approach has the advantage of having no restrictions regarding the solar cell material and technology. In this paper the description of an improved technological process for forming the microchannels is presented that is capable to avoid the previously experienced channel collapse and reduce the probability of channel cross-section shrinkage, thus achieving lower hydrodynamical resistance and better cooling performance.