Slot-die coated bulk heterojunction vs layer-by-layer organic photovoltaics: Device architecture dependent degradation

In recent years, there have been notable success stories in commercializing organic photovoltaics (OPVs) for new applications, and their record power conversion efficiency has, in parallel, increased beyond the 20% milestone. However, the still relatively low performance for large OPV modules, with limited thermal and light stability, has remained a bottleneck for wider adoption. In this study, we investigated the scalability and performance of two commonly employed OPV device architectures: inverted and conventional stacks. We explored two different strategies for photoactive layer formation: the bulk heterojunction (BHJ) method and the layer-by-layer method. All solution-processable layers were fabricated from green solvents in the air and optimized using the scalable slot-die coating technique, with PM6 as the electron donor and Y7-12 as the non-fullerene electron acceptor. In addition, we studied the degradation of the devices under thermal and light stress, placing particular emphasis on identifying thermal degradation pathways for the different device architectures. Our findings suggest that, irrespective of the device architecture, the scalable slot-die coating method can be employed to achieve high-efficiency devices, with the best power conversion efficiencies of 15.24%. The investigation indicates that minor thermal degradation occurs predominantly at the transport layer and electrode interface. Notably, inverted BHJ devices demonstrated impressive light stability, maintaining initial high performance for over 800 hours. In addition, a mini-module was fabricated, achieving a performance of 13.06%, comparable to small-scale devices. This work demonstrates the potential of slot-die coating under ambient conditions for producing high-efficiency OPV cells and modules and paves the way for developing more stable organic photovoltaics.