Fabrication And Mechanism Research Of Highly Efficient Flexible Organic Solar Cells

Organic solar cells（OSCs）have attracted enormous attention due to the great potentials of low cost,light weight,and flexibility,especially as a power supply system for wearable electronic systems（electronic textiles and synthetic skin,etc.）.The fascinating properties of flexible OSCs have been proven,but it is still a great challenging to simultaneously achieve high efficiency and mechanical robustness,especially under large deformations.Aiming at the key scientific and technical problems encountered in the development of flexible OSCs,systematic studies were carried out on the aspects of flexible device preparation,active layer morphology and mechanical properties.In this paper,eco-friendly acid was developed to prepare flexible electrodes with high conductivity and transmittance;the polymer guest effectively constructs the entangled structure morphology in active layer and improves the mechanical properties of the flexible devices;we innovatively designed structure of ultra-thin flexible device;high-performing flexible semi-transparent OSCs was obtained and highlights the potential for the cultivation of plants in greenhouses.The main results and innovations of this paper are summarized as follows:（1）The eco-friendly acid-treated EDOT:PSS（PH1000）film was developed to improve its conductivity and transmittance.Meanwhile,polyhydroxy compound doping contributes to excellent bending flexibility due to the better film adhesion between PEDOT:PSS films and PET substrate.Flexible OSCs with an efficiency of14.17%were obtained based on this electrode.After 1,000 bending cycles,the device retained over 90%of its initial efficiency.（2）The key technology for the preparation of ultrathin and ultralight OSCs was developed,and the influence mechanism of the isotropic guest(PC₇₁BM)on the photophysical properties and microstructure of the active layer was also studied.The ternary strategy introduces the third component of PC₇₁BM in D18-Cl:Y6 system,which can slightly reduce crystallization and aggregates of Y6,thereby reducing rigidity and brittleness of the active layer.The ultra-lightweight OSCs with an efficiency of 15.5%based on an ultra-thin plastic substrate（<10μm）were achieved and unmatched power-per-weight of 32.07 W g^-1 at a weight of 4.83 g m^-2 without encapsulation.（3）We have successfully improved the flexibility of the high-efficiency PBDB-T-2F:BTP-e C9 system through introducing polymer guests（PY-IT）to form entangled chain networks.When the binary blend film incorporated 10%of PY-IT,the crack-onset strain（COS）of the films can be improved by 17.14%,and the elastic modulus reduced by 9.03%of that without PY-IT.More importantly,excellent thermal stress tolerance was achieved in ternary system,which was mainly attributed to the suppression of BTP-e C9 crystallization and diffusion.A stabilized power conversion efficiency（PCE）of16.52%for flexible OSCs were achieved.（4）High-performance flexible semi-transparent OSCs were obtained by ternary active layer with an alloy-like near infrared acceptor and flexible electrode with hierarchically photonic architectures.Each band of photons could be precisely utilized and active layer could effectively trap light to improve light management in cells.This consequently resulted to PCEs of 12.04%for flexible semi-transparent OSCs with average visible transmittance of 20%.The flexible semi-transparent device exhibited low incident light angle dependence and excellent mechanical stability,maintaining over 90%of the original PCE even after 200 severe twists cycles.The potential application of flexible semi-transparent OSCs was evaluated by simulating the greenhouse environment.This is the first report on the quantitative analysis effects of semi-transparent devices on plant growth（photosynthetic efficiency and content of medicinal active ingredients）.