Importance of optical confinement in organic thin film solar cells

Abstract

We have found that the short-circuit current, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> , of polymer/fullerene [RR-P3HT/C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> ] solar cells has a clear dependence on the surface roughness of the ITO|glass substrate after the post-metallization annealing. We prepared an ITO surface with an average roughness, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> , of 1 - 9 nm by chemical etching. When solar cell structures were made on these ITO surfaces, the diffuse reflection intensity increases with the increase in ITO surface roughness. Also, the solar cell performance, J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</sub> increases drastically with ITO roughness after annealing. This feature suggests that the diffuse reflection of Al|P3HT/C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">60</sub> interface is quite important for optical confinement of the cells, after post-metallization annealing. The effect is quite effective to improve cell performances.