Molecular design of cost-effective donor polymers with high visible transmission for eco-friendly and efficient semitransparent organic solar cells

•New donor polymers for semitransparent (ST) organic solar cells have been designed.•12 low-cost D–π = A-based polymers with high visible transmission were developed.•Halogenation and quaterpolymer strategies were used for structural optimization.•Best polymer overcomes inverse relation of efficiency and visible transmission.•ST module can substitute the power source of a thermo-hygrometer under low-light.