Spectral technique for accurate efficiency measurements of emerging solar cells

•A novel spectral technique for solar cell efficiency measurement is proposed.•Spectral technique is compared with state-of-the-art solar cell efficiency measurement methods.•Accuracy: the technique provides accuracy estimation, unlike other efficiency measurement methods.•Convenience: designed for daily laboratory use, as fast and precise efficiency check.•Flexibility: can be used for variety of solar cells (perovskite, organic, dye-sensitised etc.)