Device characteristics of a 17.1% efficient solar cell deposited by a non-vacuum printing method on flexible foil

Abstract

Thin film CuInSe 2 -based (hereafter broadly referred to as CIGS) solar cells are promising due to their high efficiencies. Here, we present a 17.1% efficient CIGS solar cell produced using a low-cost non-vacuum printing method on flexible foil. This power conversion efficiency is the highest demonstrated efficiency of any thin film solar cell with the absorber deposited by non-vacuum techniques. In this paper, we compare both the champion device and median device results from our baseline process to champion devices from other laboratories. It is found that the offset between absorber bandgap and open circuit voltage (Eg/q-Voc) for the champion device is ∼0.45V, comparable to champion co-evaporated CIGS. The low (Eg/q - Voc) values for this deposition process is believed to be due to a high minority carrier lifetime in the CIGS as there is a correlation between steady-state photoluminescence (PL) intensity measured after absorber formation and (Eg/q - Voc). External quantum efficiency and spectral PL measurements were used to determine the average minimum bandgap for the champion device and the bandgap uniformity on the sub-micron length scale. The carrier collection length in the absorber layer for this deposition process was determined to be ∼1.3µm based on electron beam induced current measurements. These results demonstrate that low-cost, non-vacuum printing of CIGS can achieve comparable efficiencies and materials quality to more traditional vacuum co-evaporation and sputtering techniques.