The second part of the introduction to solar energy.Suitable for post grad students.Define and describes about Fermi Energy Level,Photovoltaic Effect,Forward and reverse bias,p-n junction etc.

1. Dr. Mrinmoy Majumder
Topic of Renewable Energy Course of MTech in Hydroinformatics Engg.
at National Institute of Technology Agartala
Enrol for my course on MCDM :
More such tutorial in http://www.baipatra.ws

2.  𝐸𝑓 = 𝐸𝑐 − 𝑘𝑇 ln
𝑁 𝑐
𝑁 𝑑
 For n type material
 𝑁𝑑 concentration of donor atom
 𝐸𝑓 = 𝐸 𝑣 − 𝑘𝑇 ln
𝑁 𝑣
𝑁 𝑎
 For n type material
 𝑁𝑑 concentration of acceptor atom

3.  When p and n type material is connected with each other then
 Electron from the n type will flow to p type material and thus become positively
charged
 Hole from p type will be compensated by the electron from n type material thus
become negatively charged
 When there is no more free electrons and holes flow of current stops and the
potential at which this equilibrium is reached is known as Contact Potential
 This condition is known as Unbiased Condition

4. If an external voltage 𝑣 𝑓 is applied on P-N junction then
the contact potential V is reduced by V- 𝑣 𝑓
The junction is said to be in Forward bias mode
Current flow across the junction increases sharply

5. If a large reverse voltage 𝑣 𝑏 is applied on P-N junction
then the contact potential V is increased by V+ 𝑣 𝑏
The junction is said to be in Reverse bias mode
Current flow is only due to minority carriers
Reverse bias condition increases the in-built potential

6.  𝐼𝑗 = 𝐼0 exp
ⅇ𝑣
𝑘𝑇
− 1
 𝐼0= saturation current or dark current under reverse bias and
 e = electronic charge

7.  When a p-n junction is illuminated by sunlight then new electronic-hole pairs are
generated and current I is obtained which is equal to :
 𝐼 = 𝐼𝐿 − 𝐼𝑗 which can be written as
 𝐼 = 𝐼𝐿 − 𝐼0 exp
ⅇ𝑣
𝑘𝑇
− 1
 where IL is solar light generated current
 This phenomenon is known as Photovoltaic Effect

8.  Figure besides depict the current-
voltage characteristic of a solar cell at
given illumination and temperature.
 Voc,Isc are the open circuit and short
circuit voltage and current,
respectively.
 Vm,Im are the voltage and current at
maximum power
 With rise in temperature leakage
increases in cell
 Cell quality is maximum when the
Fill Factor value approaches

9.  𝐹𝐹 =
𝐼 𝑚 𝑣 𝑚
𝐼𝑠𝑐 𝑣 𝑜𝑐
𝐹𝐹 =
𝐼 𝑚 𝑣 𝑚
𝐼𝑠 𝐴 𝑐
where Is is the incident solar flux
Ac is the cell’s area