Organic solar cells (OSCs) have attracted much interest in recent years for their unique properties such as flexibility, light weight and the low cost and ease of their fabrication processes. While not destined to replace silicon- based technology, organic based solar cells provide a promising technology for wearables, windows, as well as light weight constructions that cannot hold the current massive PV modules.

A lot of research has been devoted to the development of modern organic materials for solar cell devices. The development of modern and highly effective non-fullerene accepting materials has achieved great progress in organic solar cells’ (OSCs’) performance reaching a stage where device design strategies must be addressed for further enhancement.

A previous work done by our group[1] presents a device engineering approach to enhance the OPVs’ performance using modulation-doping of the hole Extraction layer (HEL). A planer heterojunction device was investigated using two well-studied standard materials 1,1-bis [(di-4-tolylamino) phenyl] cyclohexane (TAPC) as a hole transporting material, C₇₀ as the accepting material and P-type dopants, C₆₀F₄₈. The dopants were induced in a ẟ -doped layer of 10 nm width within the TAPC layer. The presence of the doped layer within the device induces an internal electric field at the junction leading to enhanced charge separation efficiency, reaching 50% enhancement in the current at the maximum power point and 30% at 0.8V_oc.

To extend the applicability of the design to cells based on modern materials produced through solution processing and make it universal to (almost) any donor-acceptor pair, we developed a strategy based on a cross-linkable high band-gap polymer matrix[2] where the donor material of choice can be blended at ~20w% to serve as the charge transporting/extracting material.[3] Being insoluble it can be considered as part of the substrate and the flexibility in choosing the transport material makes it universal. with the cooperation of a Korean research group, we also examined a thermally cross-linkable material that is highly conductive for holes which will serve not just as a host matrix for dopants, but also as a hole transporting material.

We will first describe the general properties of the enhanced charge-extraction structure utilizing Poly (vinyl carbazole) bearing cinnamate pendants (PVK-cin [50%]) as the x-linkable matrix, Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine (PTAA) as the transport/extraction material, and C₆₀F₄₈ doped PTAA as the δ-doped layer, we will also describe the properties of an HEL based on the thermally cross-linkable hole transport material X-TPACz with C₆₀F₄₈ doped X-TPACz as a δ-doped layer. [4]

Next, we describe the properties of a complete cell that is based on PBDB-T-2F (PM6) and Y6 (BTP-4F) as the donor-acceptor pair, respectively.[5, 6] We also examine the effect of using magnesium; a low work function metal an interlayer on the performance of the cell.

To place the experimental results in perspective, we conduct detailed device simulation and compare the experimentally measured enhancement to the maximum theoretical prediction.