An efficient solution-processed intermediate layer for facilitating fabrication of organic multi-junction solar cells

Photovoltaic tandem technology has the potential to boost the power conversion efficiency of organic photovoltaic devices. Here, a reliable and efficient fully solution-processed intermediate layer (IML) consisting of ZnO and neutralized poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is demonstrated for series-connected multi-junction organic solar cells (OSCs). Drying at 80°C in air is sufficient for this solution-processed IML to obtain excellent functionality and reliability, which allow the use of most of high performance donor materials in the tandem structure. An open circuit voltage (V_oc) of 0.56 V is obtained for single-junction OSCs based on a low band-gap polymer, while multi-junction OSCs based on the same absorber material deliver promising fill factor values along with fully additive V_oc as the number of junctions increase. Optical and electrical simulations, which are reliable and promising guidelines for the design and investigation of multi-junction OSCs, are discussed. The outcome of optical and electrical simulations is in excellent agreement with the experimental data, indicating the outstanding efficiency and functionality of this solution-processed IML. The demonstration of this efficient, solution-processed IML represents a convenient way for facilitating fabrication of multi-junction OSCs to achieve high power conversion efficiency. An efficient solution-processed intermediate layer is introduced for facilitating fabrication of multi-junction organic solar cells (OSCs). The multi-junction OSCs that incorporate this intermediate layer deliver promising fill factor values along with the fully additive open circuit voltage (V_oc) as the number of junctions increase.