Power conversion efficiency (PCE), lifetime and cost are critical factors to practical applications of photovoltaic cells. With the advent of the Internet of Things, vast amounts of off-grid energy sources are needed to drive low-power-consumption products for indoor applications.

However, the mature c-Si cells can't meet the application needs because their PCEs are only 2-6% under the indoor illumination conditions mainly due to the mismatch of absorption spectrum and severe charge recombination at low carrier density. Therefore, it is urgent to develop new photovoltaic cells for indoor applications.

Recently, the research team led by Prof. HOU Jianhui at Institute of Chemistry of the Chinese Academy of Sciences (ICCAS) and Prof. GAO Feng at Linkoping University in Sweden developed an organic photovoltaic (OPV) cell with outstanding efficiency under the indoor light conditions. The study was published in Nat. Energy, 2019, 4, 768.

By blending polymer donor named PBDB-TF and a carefully designed acceptor named IO-4Cl, the researchers made a photoactive layer with an absorption spectrum matching with the indoor illumination sources. The 1 cm² OPV cell achieved a PCE of 26.1% with an open-circuit voltage of 1.10V under the illumination of 1000 lux (2700 K).

Impressively, this study demonstrated that this OPV cell not only has high PCE and excellent stability but also can be made in large area. For example, the OPV cell almost maintained its initial PCE under continuous illumination after 1000 hours, and a 4cm² cell prepared via a blade-coating method can realize a PCE of over 23%.