Crystalline Silicon Photovoltaics via Low-Temperature TiO2/Si and PEDOT/Si Heterojunctions

Abstract

The most important goals in developing solar cell technology are to achieve high power conversion efficiencies and lower costs of manufacturing. Solar cells based on crystalline silicon currently dominate the market because they can achieve high efficiency. However, conventional p-n junction solar cells require high-temperature diffusions of dopants, and conventional heterojunction cells based on amorphous silicon require plasma-enhanced deposition, both of which can add manufacturing costs.

This dissertation investigates an alternative approach, which is to form crystalline-silicon-based solar cells using heterojunctions with materials that are easily deposited at low temperatures and without plasma enhancement, such as organic semiconductors and metal oxides. We demonstrate a heterojunction between the organic polymer, poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT), and crystalline silicon, which acts as a hole-selective contact and an alternative to a diffused p-n junction. We also present the use of a heterojunction between titanium dioxide and crystalline silicon as a passivating electron-selective contact. The Si/TiO2 heterojunction is demonstrated for the first time as a back-surface field in a crystalline silicon solar cell, and is incorporated into a PEDOT/Si device. The resulting PEDOT/Si/TiO2 solar cell represents an alternative to conventional silicon solar cells that rely on thermally-diffused junctions or plasma-deposited heterojunctions. Finally, we investigate the merits of using conductive networks of silver nanowires to enhance the photovoltaic performance of PEDOT/Si solar cells. The investigation of these materials and devices contributes to the growing body of work regarding crystalline silicon solar cells made with selective contacts.