Investigation of Organic Bulk Heterojunction Solar Cells from Optical Aspect

Abstract

Low in cost, light in weight and flexible in mechanics, the solution-processed organic solar cells have aroused worldwide interest and have been the promising alternative to the tradi‐ tional silicon-based solar cells [1-4]. However, they are still not available for the commercial‐ ization due to their low power conversion efficiency (PCE). Therefore, many research works have focused on the employing of new materials and device structures to improve the de‐ vice performance. The milestone is the introduction and application of the bulk heterojunc‐ tion structure consisting of an interpenetrating network of electron donor and acceptor materials [5]. By using this structure, the conventional organic solar cell (OSC) with poly(3hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) blend shows a su‐ perior performance. Recently, the inverted organic solar cell (IOSC, in which the polarities of the two electrodes are exchanged) has also been introduced as the possible candidate for OSC to remedy the low air stability of OSC [6]. Both OSC and IOSC are now attracting the research interest. However, most of the previous works are mainly done for OSC or IOSC separately, and almost no researches are reported about the systemic comparison between OSC and IOSC for their different performances besides the air stability. Since the reported PCE of IOSC is relatively lower than that of OSC in many researches, one may doubt that which structure is better, the conventional one or the inverted one? As a result, one section of this chapter aims to investigate the performance differences of OSC and IOSC.