1. ELEG 620 Solar Electric Power Systems March 4, 2010 Solar Electric Power Systems ELEG 620 Electrical and Computer Engineering University of Delaware March 4, 2010

2. ELEG 620 Solar Electric Power Systems March 4, 2010

3. ELEG 620 Outcomes 1.Understanding the nature of Solar Radiation 2. Design of a solar cell from first principles 3. Design of a top contact system 4. Design, construction and test of a solar power system

4. ELEG 620 Solar Electric Power Systems March 4, 2010 Solar Cell Design Silicon Solar Cell Design Homework Due: March 9, 2010 Design a silicon solar cell. Calculate the following: 1.Light generated current at short circuit 2.Open circuit voltage 3.Maximum power (show voltage and current at maximum power) 4.Efficiency 5.Thickness and doping of each layer Show key equations

5. ELEG 620 Solar Electric Power Systems March 4, 2010 Solar Cell Design Silicon Solar Cell Design Homework Due: March 9, 2010 Design a silicon solar cell. Following assumptions can be used Structure is N on P There is no surface recombination There is no surface reflection Series resistance = 0 ohms Shunt resistance is infinite (shunt conductance = 0) Sunlight = AM 1.5 global

6. I-V Curve of a Well Behaved Solar Cell I-V curve of a well behaved solar cell Voltage(V) Current (mA) 0.5 -0.5 1 20 40 60 -20 -40 -60 (Vmp,Imp) Voc Isc I Diode _ + V I Light I ELEG 620 Solar Electric Power Systems March 4, 2010

10. Solar Cell Design

11. J o = q tanh D p n i 2 L p N d XjXj LpLp + D n n i 2 L n N a XjXj LnLn q ELEG 620 Solar Electric Power Systems March 4, 2010

12. J o = q D p n i 2 L p N d + D n n i 2 L n N a q ELEG 620 Solar Electric Power Systems March 4, 2010

13. LifetimeVoltage (mV) 1 ms561 100us506 10us467 Wn (um) Wp (um) S (cm/s) De (cm 2 /s) Dh (cm 2 /s) N D (cm- 3 ) N A (cm- 3 ) Jsc (mA/cm 2 ) 10500035121e151e1443.6 ELEG 620 Solar Electric Power Systems March 4, 2010

14. Wn (um) Wp (um) S (cm/s) De (cm 2 /s) Dh (cm 2 /s) N D (cm- 3 ) N A (cm- 3 ) Jsc (mA/cm 2 ) 10um500035121e151e1443.6 1500035121e161e1543.6 LifetimeVoltage (mV) 1 ms561620 100us506565 10us467526 ELEG 620 Solar Electric Power Systems March 4, 2010

15. Design rules for high performance For a high solar cell efficiency, simultaneously need high absorption, collection, open circuit voltage and fill factor. Absorption and collection are typically achievable by “clever” engineering & innovation. Voltage is controlled by worst, localized region, NOT the same region which absorbs the light – this is fundamentally why single crystal solar cells are highest efficiency. Predictive models and design rules for all characteristics are necessary for the device parameters.

16. ELEG 620 Solar Electric Power Systems March 4, 2010 Solar Cell Operation Key aim is to generate power by: (1) Generating a large short circuit current, I sc (2) Generate a large open-circuit voltage, V oc (3) Minimise parasitic power loss mechanisms (particularly series and shunt resistance).

17. Structure, Equivalent circuit and IV curve of solar cell I light Equivalent circuit of solar cell I-V Characteristic of Solar Cell + V Base Emitter Back contact Front contact I V 0 I sc V oc P max ELEG 620 Solar Electric Power Systems March 4, 2010

18. Maximizing efficiency  = I sc V oc FF P in  I sc  E G  Reflection Surface Metal  L n, L p  S r x j optimum  V oc  E G  doping  L n, L p  S r  FF  Series R Metal Emitter  doping Thick emitter Doping and diffusion length are related

19. J n = qu n n E qD n dndn dxdx + J p = qu p p E qD p dpdp dxdx - ELEG 620 Solar Electric Power Systems March 4, 2010