Please anyone explain me about active layer, ETL, HTL working function
You need active layer with a right band gap, ~1.1 eV, to absorb photons (sun light). The photon then excites a electron from valence band (or HOMO if molecule) to conduction band (or LUMO if molecule), leaving a hole in the valence band. The electron-hole pair will subsequently get separated by the build-in potential close to a junction(p-n or metal-semiconductor), and then you need the ETL and HTL to transport the electron and hole to the corresponding electrodes to generate electricity.
Adding to what has been aid by the colleagues above, the active layer has the function of photon absorption and generation of excitons which are bound electron hole pairs. In organic material where the dielectric constant is relatively small, the screening between the electron hole pairs will be smaller and the binding energy will appreciable. To get a photovoltaic effect the electron must be separated from holes in the excitons. This is accomplished by a process called dissociation. Dissociation is achieved by proper potential energy gradients at the sides of the active layer, from one side for holes by the HTL and the other side by electrons by the ETL.
In metallic semiconductors with high dielectric constant the exciton are readily dissociated at room temperature and the electron hole pairs are separated by the junction field region. So, there is no need for the ETL and HTL they are available as p-side and n- side of the junction.
wish you success
Ok @ any, I have read in one paper Semiconductor oxides replaces PCBM. Because 1. low cost, 2. They have wide band gap so they can accept electrons easily. Suppose ZnO acts as electron acceptor, then what is the use of active layer here. What is its role i don't understand. Please anybody Knows answer me
Dear Sangeetha,
To answer your last question, it is so that the the transport layers at the sides of the active layer must have the following properties to perform their function in separating the electrons and holes from the excitons and transport the cathode and anode>
The electron transport layer may have a conduction band edge lower than that of the absorber to extract the electrons from the excitons reaching to this layer by diffusion. at the same time the ETL must reject the holes by having tits valence band edge lower than that of the absorber. In addition the ETL must able to conduct electrons by having high electron mobility. These conditions are satisfied by some materials including PCBM and oxides semiconductor such as ZO .
Concerning the HTL it must have valence band edge higher than that of the absorber and to extract holes from it and it must have higher conduction band edge higher than that of the absorber to reject the electrons. The HTL must be good hole conducting.
wish you success.
Dear Abdehalim ZnO is having higher electron mobility. Can we use ZnO only without using active layer.
Active layer captures photon energy of pre-specified wavelength. Before recombination, charge carriers get separated by built-in electric field of depletion layer. ETL and HTL carry electron and hole towards electrodes for fruitful operation of organic and perovskite solar cell. You may check the following link:
https://www.sciencedirect.com/science/article/abs/pii/S2352492821008722
- Badges
- Science topic