# 20.109(S15):Wrap-up and data summary (Day 6)

20.109(S15): Laboratory Fundamentals of Biological Engineering

## Introduction

Last time, you learned the solar conversion efficiency of the DSSC that you personally manufactured, and started to get a sense of how your condition compared to others. (Note: In a previous year, typical efficiencies ranged from about 1.5-5.5%.) Today you will finish interpreting and writing up this class-wide data.

To calculate DSSC efficiency, you also measured the open circuit voltage (Voc) and short circuit current (Isc). Separately, you quantified the DSSC fill factor, which essentially measures how well the device performs compared to its ideal capacity. You can learn much more about these measures at the [pveducation.org Photovoltaic Education Network website], particularly the Solar Cell Operation section. Some brief context about Voc and Isc is also included below, modified from the 20.309 Electronics Primer that one of your instructors helped write.

Figure 1: Resistor with terminal parameters defined. The voltage across and current through the element are shown.

First, recall that current (i) reflects the flow rate of charge carriers such as electrons, while voltage (v) reflects the electrical potential difference between two points. The higher the voltage, the greater the current flow through a circuit element such as a resistor, all else being equal. Finally, note that resistance reflects the tendency of an element to draw current and also its tendency to dissipate energy. A linear resistor obeys Ohm’s law, ${\displaystyle v=iR}$, at any instant in time.

Two limiting cases of the resistor element are the open circuit and the short circuit (Fig. 2). Infinite resistance means that no current passes through that element; this is also called an open circuit across said element and is equivalent to an unconnected port. Zero resistance means no potential difference appears across the element; this is also called a short circuit across that element and is equivalent to an ideal wire. In a device such as your solar cell, the values Voc and Isc are the maximum voltage and current that the device can attain, and their product is the ideal maximum power available. In turn, a high fill factor indicates low energy dissipation (through resistance internal to the device) and near ideal operation.

Figure 2: Open and short circuits. In the open circuit (left), the maximum potential difference exists across the resistor, and ${\displaystyle V_{AB}=V}$. In the short circuit (right), the potential is the same everywhere because a wire connects the two resistor terminals, and ${\displaystyle V_{AB}=0}$.

## Protocols

### Part 1: Complete mini-report

Working with your partner, write a short report describing the Module 3 work according to the linked specifications.

Please print a hardcopy of the report (double-sided, please!) before you leave in addition to submitting on Stellar. You may print just the text if the figures exceed the printer memory capacity.

### Part 2: Closing down the lab...

Some time during lab, find 10-15 minutes to complete your section-specific items on the clean-up/inventory document.

## Homework

1. Prepare a 12 minute powerpoint talk that describes the research question you have identified, how you propose to study the question, and what you hope to learn. More detailed descriptions of the elements of the oral presentation can be found in the Homework assignments and the protocols associated with this Module, as well as in the research proposal guidelines. When it is ready, please submit your presentation to Stellar. Speaking order will be determined by the order that presentations are received.

Next Day: Student proposal presentations

Previous Day: Solar cell testing