Abstract

We present 10-nm thick metal alloys created by coevaporation of calcium and silver as transparent top electrode for inverted bulk heterojunction small-molecule organic solar cells (SMOSC). It is shown that such alloys exhibit sufficiently high conductivity to replace previously used thicker (>14 nm) pure Ag contacts. At the same time, Ca:Ag alloys have higher transmittance compared to pure Ag, which is desirable for semitransparent SMOSC where the light passes through the device and the metal contact. We find that a metal contact consisting of 1 nm Ag underlayer and 10 nm Ca:Ag of 1:1 mixing ratio (total Ag content by volume of 6 nm) on glass has an average transmittance in the visible range of 76% with a sheet resistance of 27.1 Ω/□, approaching the performance of ITO while being applied by a much gentler deposition method. Application of 10-nm thick alloys in semitransparent SMOSC lead to transmittance in the visible range Tvis of up to 49% and efficiency η of up to 2.3%, showing superior performance compared to devices with pure Ag top contacts.

Abstract

A new irradiance adjustment system for the light source named “Programmable Reference cell system for Irradiance adjustment by Spectral Measurement (PRISM)” has been developed for photovoltaics evaluation. It can be applied for various kinds of solar cells and illumination conditions without the preparation of conventional reference cells. This system consists of a device for absolute spectral responsivity measurements, that is, the spectral responsivity unit, and a device for irradiance adjustment of the light source, that is, the spectral reference cell. First, the short circuit current of the target solar cell (Iref) is calculated by convolution of the absolute spectral responsivity with the spectral irradiance under STC (AM1.5 G, 1 kW/m2, 25°C) as defined in IEC 60904-3. The spectral irradiance of the light source is then adjusted for I–V measurements so that the short-circuit current of the spectral reference cell (Ical), calculated by convolution of the absolute spectral responsivity with the spectral irradiance of the light source, agrees with Iref. The difference between Iref and the short circuit current, as determined at an internationally recognized test center under STC, was within ±2% for crystalline silicon solar cells and ±3% for organic solar cells. The difference between Ical and the short-circuit current measured under a solar simulator or LED in which the irradiance was adjusted by this system was within ±4% when the irradiance was higher than 4 W/m2.