The purpose of the thesis is enhancing efficiency of asymmetric quantum dots (AMQD) solar cells. The AMQD structures are grown on the n-type GaAs substrate by (MBE). In order to enhance the photovoltaic characteristics, we introduce InGaAs quantum well (QW) and modulation doping in the well to investigate effect of the strain relief and built-in electric field in the active layer. In our experiment, we analyze the optical property of AMQD structures by photoluminescence measurement system, and then decompose emission wavelength by Gaussian fitting to find optical characteristics of each single layer quantum dots. Besides, we also measure photocurrent spectra, external quantum efficiency, electrical absorption, and electro reflectance spectra to discuss carrier transition inside AMQD structure . Finally, we acquire the photovoltaic basic parameter under one sun. The results show that QDs provide additional photocurrent via absorbing extra photons, but the open circuit voltage decrease seriously due to the accumulated strains. So as to relieve the strains and enhance carriers extraction, we introduce QW layers with different growth temperatures and change the modulation doping concentrations . From the results, the higher growth temperature for QW diminishes accumulated strains, and the higher p-type modulation doping concentration indicates an extraction enhancement due to the stronger built-in electric field. By optimizing QW growth conditions, the efficiency has overtaken GaAs baseline cells. In addition, we improve the photon-excited current collection by using matrix pattern and wet etching on the device surface, the best photovoltaic characteristic shows V OC = 0.74 V, J SC = 18.82 mA/cm2, FF = 0.78, £b= 10.86%.