What are the parameter requirements for solar polymer batteries?
The equivalent circuit diagram of the solar polymer battery and the current-voltage characteristic curve are shown in the figure:
The equivalent circuit diagram of the organic solar photopolymer battery
Current-voltage characteristic curve
For organic solar polymer batteries, the main evaluation parameters are as follows:
(1) Open circuit voltage ( Voc): refers to the terminal voltage of the solar polymer battery when the current is zero when the current is zero, and it is also the maximum voltage generated by the solar battery, usually in V. The open circuit voltage of the solar polymer battery is related to the light intensity, temperature and acceptor material, and mainly depends on the energy level difference between the HOMO energy of the donor and the LUMO energy of the acceptor:
(2) Short-circuit current (Jsc): The short-circuit current is the current that passes when the voltage and resistance are both zero, that is, the current of the device without external electric field bias, is the maximum output current of the solar cell, and the unit is mA.cm.
The main factors affecting the magnitude of the short-circuit current are: the absorption of sunlight by the active layer, the quantum efficiency of charge separation, the transport of carriers in the material, and the loss during the transport process.
(3) Fill factor (FF): It is defined as the ratio of the maximum power of the solar polymer battery to the product of the open circuit voltage and the short-circuit current, which illustrates the maximum output power that the solar polymer battery can provide In the formula, Vmax refers to the maximum output voltage; Imax refers to the maximum output current; Pmax refers to the maximum output power. From the volt-ampere characteristic curve, we can see that FF is the ratio of the area of u200bu200bthe two rectangles in the figure, dimensionless, and the FF of an ideal solar cell is 1. The main factors affecting the size of the fill factor are: the contact resistance between the composite film and the electrode, the carrier mobility in the composite film, the thickness of the composite film, and the defects in the device!
(4) Energy conversion efficiency (PCE): In the solar polymer battery, the energy conversion efficiency (PCE) is one of its most important parameters, which is defined as the maximum output power and the incident light intensity The ratio of Pin, namely:
It can be seen from the above formula that the energy conversion efficiency of solar polymer cells is closely related to open circuit voltage, short circuit current, fill factor and light intensity.
(5) External quantum efficiency (IPCE): External quantum efficiency is the ratio of the number of electrons generated in the external circuit to the total number of incident photons. Its definition formula is:
In the formula, Pin is the incident light power, and input is the wavelength of the incident monochromatic light.
From the above formula, it can be found that open circuit voltage, short circuit current, fill factor and other factors are the key factors that affect the energy conversion efficiency of polymer solar cells. Methods to improve the volt-ampere characteristics of solar cells include increasing the open-circuit voltage, short-circuit current, and fill factor, and make them tend to be the volt-ampere characteristics of ideal solar polymer cells. The short-circuit current is proportional to the intensity of the absorbed light (the number of photons absorbed per unit area and unit time). It seems that increasing the thickness of organic matter can greatly increase the intensity of light absorption, but the diffusion distance of excitons or the carrier The recombination length of the current must be greater than the thickness of the organic material, because the mobility of excitons and charge carriers of the semiconducting polymer material is relatively low . This bottleneck makes the maximum optimized thickness of the device 100-200nm, which is equivalent to the light absorption depth (100nm) . In addition, the spectral response of the solar polymer battery does not respond well to the range of the solar spectrum. The spectral response range is relatively narrow. Only the wavelength of the maximum absorption peak position can produce a relatively strong response. Other absorption peaks The response of the wavelength is weaker, so the energy conversion efficiency under ordinary white light is much weaker than the energy conversion efficiency of the monochromatic light at the absorption peak. In addition, after the device is prepared, there are many more links on the transmission road of light energy conversion to electric energy, and each link has different degrees of photoelectric conversion loss. This series of links will cause the reduction of photoelectric efficiency.