Photosensitised silicon solar cells: progress and challenges

We present historical context and review recent advances in the realisation of a photosensitised silicon solar cell, highlighting key theoretical and experimental developments. Emphasis is placed on the importance of electrostatic near-field interaction between the transition dipole moments of the luminophore and electron-hole pairs in the silicon crystal at a distance of a few nanometres. The very fast energy transfer then resembles the Förster resonance energy transfer between two molecules. Photon tunnelling via the evanescent field of the excited molecule ('optical near field') into optical states in silicon occurs at somewhat larger separation between the molecule and silicon, of the order of tens of nanometres. Accessing the critical Förster regime relies on oxide-free silicon surfaces and the covalent attachment of dyes, enabling efficient passivation and precise control of interface chemistry. Realising a complete photosensitised silicon solar cell remains a challenge and we outline promising directions and review recent progress that brings this goal closer to reality.