Semitransparent polymer solar cells with 9.06% efficiency and 27.1% average visible transmittance obtained by employing a smart strategy

Opaque and semitransparent polymer solar cells (PSCs) were prepared with the narrow band gap donor PTB7-Th and the ultra-narrow band gap acceptor IEICO-4F by optimizing their doping ratios. The power conversion efficiency (PCE) of opaque PSCs can be maintained at over 11% by altering PTB7-Th:IEICO-4F ratios from 1.4:1.5 to 0.8:1.5 (wt/wt), along with a red-shifted absorption edge of active layers. The red-shifted absorption edge should be attributed to IEICO-4F molecular aggregation due to the relatively increased IEICO-4F content in active layers. The increased photon harvesting in the near infrared light range due to IEICO-4F molecular aggregation and decreased photon harvesting in the visible light range with lower PTB7-Th content provide great potential to prepare efficient semitransparent PSCs. The semitransparent PSCs were prepared with 1 nm Au/11 nm Ag replacing 100 nm Al as the electrode. The average visible transmittance (AVT) of semitransparent PSCs is increased from 23.7% to 27.1% by decreasing the PTB7-Th content in active layers, along with a slight PCE decrease from 9.48% to 9.06% and a lower cost. The optimized 9.06% PCE and 27.1% AVT should be impressive values for semitransparent PSCs. This work may provide a smart strategy to achieve efficient semitransparent PSCs with low cost by decreasing the narrow band gap donor content in active layers.