P3HT as a pinhole blocking back contact for CdTe thin film solar cells

Abstract

A new approach to back contacting CdTe solar cells that uses an organic poly(3-hexythiophene-2,5-diyl) (P3HT) back contact layer is reported. The most striking benefit of P3HT was demonstrated to be through a “pinhole blocking” effect, significantly improving performance uniformity. This was demonstrated through comparison of open circuit voltage values for a large sample set (600 cells) and through measurement of a device with a graded absorber layer thickness (0.7–1.9 µm). The conversion efficiency achievable and the electrical barrier height of the contacts to the CdTe were also investigated for P3HT/Au and Au control contacts – both being tested with and without additional Cu. Temperature dependent JV measurement showed the use of P3HT reduced the barrier to (0.29–0.33 eV) from the value achievable with Au (0.39–0.42 eV), but inclusion of Cu into either of the structures gave the lowest barriers (0.21–0.22 eV). For the data sets recorded, P3HT/Au yielded higher peak efficiencies than the Au control contact. However, when Cu was included the peak performance of devices having P3HT/Cu/Au and Cu/Au contacts were comparable at 14.7% respectively but the P3HT/Cu/Au contact displayed a significantly higher average performance through increased uniformity of the device response.