| Thin-film solar cells based on Cu(In,Ga)Se2(CIGS)absorber layers on flexible polyimide(PI)substrate has a lot of advantages: They are lightweight,they can be rolled up when not in use,their excellent ratio of mass-power make them ideal candidates for space.From the industrial point of view,flexible cells offer the considerable advantage to allow manufacturing with a roll-to-roll deposition process,which would reduces production costs significantly.Up to now,EMPA(Swiss Federal Laboratories for Materials Science and Technology)has achieved 20.4% in small areas,which is the highest efficiency reported about flexible CIGS solar cells.Different with soda lime glass(SLG),PI is known as lack of alkali metals such as sodium and potassium.The doping of a small amount of alkali metals into the CIGS absorber layer is beneficial for performance of solar cell devices.The crystallization quality and electrical properties of CIGS thin films improved apparently.The effects of alkali metals addition lead to improved conversion efficiencies mainly by enhancing the open circuit voltage(Voc)and fill factor(FF)of the devices.In this work,the CIGS absorber layer was deposited by the continuous evaporation process at a low substrate temperature.The first part studied the effect of different sodium doping methods on the CIGS thin film on the flexible substrate,including pre-doping,post-doping and Na-doping in co-evaporation methods,investigating CIGS absorber physical properties by a series of test,Co-evaporation Na doping process can improve the electrical properties of CIGS effectively,and suitable for large-scale industrial production.In the second part,the effect of K-doping into CIGS absorber was investigated.In order to find the optimized evaporate of KF,it can be changed by evaporate temperature,evaporate time and annealed temperature,therefore,it is suggested that post-deposition treatment of KF is more optimized method by investigated the surface structure and electrical properties of CIGS thin films.Finally,the conversion efficiency of flexible Cu(In,Ga)Se2 thin film solar cell on polyimide substrate is achieved to be 12.9% by optimizing the post-K-doping method. |
